View source for Biomolecular condensate

{{Short description|Class of membrane-less organelles within biological cells}}
{{See also|Cytoplasmic inclusions}}
[[File:Formation and examples of membraneless organelles.png|thumb|Formation and examples of membraneless organelles]]

In [[biochemistry]], '''biomolecular condensates''' are a class of [[lipid bilayer|membrane]]-less [[organelles]] and organelle subdomains, which carry out specialized functions within the [[cell (biology)|cell]]. 

Unlike many organelles, biomolecular condensate composition is not controlled by a bounding membrane. Instead, condensates can form and maintain organization through a range of different processes, the most well-known of which is [[phase separation]] of [[protein]]s, [[RNA]], and other [[biopolymers]] into either [[colloid]]al emulsions, [[gel]]s, [[liquid crystal]]s, solid [[crystals]], or [[protein aggregation|aggregates]] within cells.<ref name=":4">{{Cite journal |last1=Garaizar |first1=Adiran |last2=Espinosa |first2=Jorge R. |last3=Joseph |first3=Jerelle A. |last4=Collepardo-Guevara |first4=Rosana |date=2022-03-15 |title=Kinetic interplay between droplet maturation and coalescence modulates shape of aged protein condensates |journal=Scientific Reports |language=en |volume=12 |issue=1 |pages=4390 |doi=10.1038/s41598-022-08130-2 |pmid=35293386 |pmc=8924231 |bibcode=2022NatSR..12.4390G |issn=2045-2322}}</ref>

== History ==

=== Micellar theory ===
[[File:PSM V56 D0733 Starch granules of corn.png|thumb|Starch granules of corn]]

The micellar theory of [[Carl Nägeli]] was developed from his detailed study of '''[[starch]] granules''' in 1858.<ref>{{Cite journal |last=Farlow |first=William G. |title=Karl Wilhelm von Naegeli |journal=Proceedings of the American Academy of Arts and Sciences |year=1890 |volume=26 |pages=376–381 |jstor=20013496}}</ref> Amorphous substances such as starch and cellulose were proposed to consist of building blocks, packed in a loosely crystalline array to form what he later termed "micelles". Water could penetrate between the micelles, and new micelles could form in the interstices between old micelles. The swelling of starch grains and their growth was described by a molecular-aggregate model, which he also applied to the cellulose of the plant cell wall. The modern usage of '[[micelle]]' refers strictly to lipids, but its original usage clearly extended to other types of [[biomolecule]], and this legacy is reflected to this day in the description of milk as being composed of '[[casein]] micelles'.

=== Colloidal phase separation theory ===
[[File:Parasite130059-fig7 Spermiogenesis in Pleurogenidae (Digenea).tif|thumb|Glycogen granules in Spermiogenesis in Pleurogenidae (Digenea)]]

The concept of intracellular [[colloid]]s as an organizing principle for the compartmentalization of living cells dates back to the end of the 19th century, beginning with [[William Bate Hardy]] and [[Edmund Beecher Wilson]] who described the [[cytoplasm]] (then called '[[protoplasm]]') as a [[colloid]].<ref>{{cite journal | vauthors = Wilson EB | title = The Structure of Protoplasm | journal = Science | volume = 10 | issue = 237 | pages = 33–45 | date = July 1899 | pmid = 17829686 | doi = 10.1126/science.10.237.33 | bibcode = 1899Sci....10...33W | url = https://zenodo.org/record/2117300 }}</ref><ref>{{cite journal | vauthors = Hardy WB | title = On the structure of cell protoplasm: Part I. The Structure produced in a Cell by Fixative and Post-mortem change. The Structure of Colloidal matter and the Mechanism of Setting and of Coagulation | journal = The Journal of Physiology | volume = 24 | issue = 2 | pages = 158–210.1 | date = May 1899 | pmid = 16992486 | pmc = 1516635 | doi = 10.1113/jphysiol.1899.sp000755 }}</ref> Around the same time, [[Thomas Harrison Montgomery Jr.]] described the morphology of the [[nucleolus]], an organelle within the nucleus, which has subsequently been shown to form through intracellular phase separation.<ref>{{cite journal | vauthors = Montgomery T | title = Comparative cytological studies, with especial regard to the morphology of the nucleolus | journal = Journal of Morphology | volume = 15 | issue = 1 | pages = 265–582 | date = 1898 | doi = 10.1002/jmor.1050150204 | s2cid = 84531494 | url = https://archive.org/details/comparativecytol00mont }}</ref> [[William Bate Hardy|WB Hardy]] linked formation of biological [[colloid]]s with phase separation in his study of [[globulins]], stating that: "The globulin is dispersed in the solvent as particles which are the colloid particles and which are so large as to form an internal phase",<ref>{{cite journal | vauthors = Hardy WB | title = Colloidal solution. The globulins | journal = The Journal of Physiology | volume = 33 | issue = 4–5 | pages = 251–337 | date = December 1905 | pmid = 16992817 | pmc = 1465795 | doi = 10.1113/jphysiol.1905.sp001126 }}</ref> and further contributed to the basic physical description of oil-water phase separation.<ref>{{cite journal | vauthors = Hardy WB | title =  The tension of composite fluid surfaces and the mechanical stability of films of fluid. | journal = Proceedings of the Royal Society A | volume = 86 | issue = 591 | date = 1912 | pages = 610–635 | doi = 10.1098/rspa.1912.0053 | bibcode = 1912RSPSA..86..610H | doi-access = free }}</ref>

[[Colloid]]al [[phase separation]] as a driving force in cellular organisation appealed strongly to [[Stephane Leduc]], who wrote in his influential 1911 book ''The Mechanism of Life'': "Hence the study of life may be best begun by the study of those physico-chemical phenomena which result from the contact of two different liquids. Biology is thus but a branch of the physico-chemistry of liquids; it includes the study of electrolytic and colloidal solutions, and of the molecular forces brought into play by solution, osmosis, diffusion, cohesion, and crystallization."<ref>{{Cite web|url=http://www.gutenberg.org/files/33862/33862-h/33862-h.htm|title=The Mechanism of Life| vauthors = Leduc S |year=1911}}</ref>

The [[primordial soup]] theory of the origin of life, proposed by [[Alexander Oparin]] in Russian in 1924 (published in English in 1936)<ref name="Oparin">{{Cite web|url=http://breadtagsagas.com/wp-content/uploads/2015/12/AI-Oparin-The-Origin-of-Life.pdf|title=The Origin of Life| vauthors = Oparin A }}</ref> and by [[J.B.S. Haldane]] in 1929,<ref>{{Cite web |url= http://www.uv.es/~orilife/textos/Haldane.pdf |title=The Origin of Life| vauthors = Haldane JB }}</ref> suggested that life was preceded by the formation of what Haldane called a "hot dilute soup" of "[[colloid]]al organic substances", and which Oparin referred to as '[[coacervate]]s' (after de Jong<ref>{{cite journal | vauthors = Bungenberg de Jong HG, Kruyt HR | title = Coacervation (partial miscibility in colloid systems | journal = Proc. K. Ned. Akad. Wet 1929 | volume = 32 | pages = 849–856 }}</ref>) – particles composed of two or more [[colloid]]s which might be protein, lipid or nucleic acid. These ideas strongly influenced the subsequent work of [[Sidney W. Fox]] on proteinoid microspheres.

=== Support from other disciplines ===
[[File:Micelle caseine.svg|thumb|Micelle caseine]]

When cell biologists largely abandoned [[colloid]]al phase separation, it was left to relative outsiders – agricultural scientists and physicists – to make further progress in the study of phase separating biomolecules in cells.

Beginning in the early 1970s, Harold M Farrell Jr. at the US Department of Agriculture developed a [[colloid]]al [[phase separation]] model for milk '''[[casein]] micelles''' that form within mammary gland cells before secretion as milk.<ref>{{cite journal | vauthors = Farrell HM | title = Models for casein micelle formation | journal = Journal of Dairy Science | volume = 56 | issue = 9 | pages = 1195–206 | date = September 1973 | pmid = 4593735 | doi = 10.3168/jds.S0022-0302(73)85335-4 | doi-access = free }}</ref>

Also in the 1970s, physicists Tanaka & Benedek at MIT identified phase-separation behaviour of [[Crystallin#Beta and gamma crystallin|gamma-crystallin]] proteins from lens [[Epithelium|epithelial]] cells and [[cataract]]s in solution,<ref name="Observation of protein diffusivity">{{cite journal | vauthors = Tanaka T, Benedek GB | title = Observation of protein diffusivity in intact human and bovine lenses with application to cataract | journal = Investigative Ophthalmology | volume = 14 | issue = 6 | pages = 449–56 | date = June 1975 | pmid = 1132941 }}</ref><ref name="Phase separation of a protein-water">{{cite journal | vauthors = Tanaka T, Ishimoto C, Chylack LT | title = Phase separation of a protein-water mixture in cold cataract in the young rat lens | journal = Science | volume = 197 | issue = 4307 | pages = 1010–2 | date = September 1977 | pmid = 887936 | doi = 10.1126/science.887936 | bibcode = 1977Sci...197.1010T }}</ref><ref name="Cytoplasmic phase separation in for">{{cite journal | vauthors = Ishimoto C, Goalwin PW, Sun ST, Nishio I, Tanaka T | title = Cytoplasmic phase separation in formation of galactosemic cataract in lenses of young rats | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 76 | issue = 9 | pages = 4414–6 | date = September 1979 | pmid = 16592709 | pmc = 411585 | doi = 10.1073/pnas.76.9.4414 | doi-access = free | bibcode = 1979PNAS...76.4414I }}</ref><ref name="ThomsonSchurtenberger1987">{{cite journal | vauthors = Thomson JA, Schurtenberger P, Thurston GM, Benedek GB | title = Binary liquid phase separation and critical phenomena in a protein/water solution | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 84 | issue = 20 | pages = 7079–83 | date = October 1987 | pmid = 3478681 | pmc = 299233 | doi = 10.1073/pnas.84.20.7079 | doi-access = free | bibcode = 1987PNAS...84.7079T }}</ref><ref name="Binary-liquid phase separation of l">{{cite journal | vauthors = Broide ML, Berland CR, Pande J, Ogun OO, Benedek GB | title = Binary-liquid phase separation of lens protein solutions | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 88 | issue = 13 | pages = 5660–4 | date = July 1991 | pmid = 2062844 | pmc = 51937 | doi = 10.1073/pnas.88.13.5660 | doi-access = free | bibcode = 1991PNAS...88.5660B }}</ref> which Benedek referred to as ''''protein condensation''''.<ref name="iovs.org">{{cite journal | vauthors = Benedek GB | title = Cataract as a protein condensation disease: the Proctor Lecture | journal = Investigative Ophthalmology & Visual Science | volume = 38 | issue = 10 | pages = 1911–21 | date = September 1997 | pmid = 9331254 | url = http://www.iovs.org/cgi/reprint/38/10/1911 }}</ref>

[[File:Hand-book of physiology (1892) (14763034584).jpg|thumb|Lens epithelium containing crystallin. Hand-book of physiology (1892)]]

In the 1980s and 1990s, [[Athene Donald]]'s [[polymer physics]] lab in Cambridge extensively characterised [[phase transition]]s / [[phase separation]] of '''[[starch]] granules''' from the [[cytoplasm]] of plant cells, which behave as [[liquid crystal]]s.<ref>{{cite journal | vauthors = Waigh TA, Gidley MJ, Komanshek BU, Donald AM | title = The phase transformations in starch during gelatinisation: a liquid crystalline approach | journal = Carbohydrate Research | volume = 328 | issue = 2 | pages = 165–76 | date = September 2000 | pmid = 11028784 | doi = 10.1016/s0008-6215(00)00098-7 }}</ref><ref>{{Cite journal|doi=10.1016/S0008-6215(98)00079-2|title=Gelatinisation of starch: A combined SAXS/WAXS/DSC and SANS study|journal=Carbohydrate Research|volume=308|issue=1–2|page=133|year=1998| vauthors = Jenkins PJ, Donald AM }}</ref><ref>{{cite journal | vauthors = Jenkins PJ, Donald AM | title = The influence of amylose on starch granule structure | journal = International Journal of Biological Macromolecules | volume = 17 | issue = 6 | pages = 315–21 | date = December 1995 | pmid = 8789332 | doi = 10.1016/0141-8130(96)81838-1 }}</ref><ref>{{Cite journal| vauthors = Jenkins PJ, Cameron RE, Donald AM |author-link3=Athene Donald|doi=10.1002/star.19930451202|title=A Universal Feature in the Structure of Starch Granules from Different Botanical Sources|journal=Starch - Stärke|volume=45|issue=12|page=417|year=1993}}</ref><ref>{{Cite journal| vauthors = Donald AM, Windle AH, Hanna S |author-link1=Athene Donald |doi=10.1063/1.2809100|title=Liquid Crystalline Polymers|journal=Physics Today|volume=46|issue=11|page=87|year=1993|bibcode = 1993PhT....46k..87D |hdl=2060/19900017655|hdl-access=free}}</ref><ref>{{cite book|author1=Windle, A.H. |author2=Donald, A.D. |title=Liquid crystalline polymers|publisher=Cambridge University Press|location=Cambridge, UK|year=1992|isbn=978-0-521-30666-9}}</ref><ref>{{cite book|title=Starch: structure and functionality|publisher=Royal Society of Chemistry|location=Cambridge, England|year=1997|isbn=978-0-85404-742-0}}</ref><ref>{{cite book|title=The importance of polymer science for biological systems: University of York|date=March 2008|publisher=Royal Society of Chemistry|location=Cambridge, England|isbn=978-0-85404-120-6}}<!--|access-date=7 April 2016--></ref>

In 1991, [[Pierre-Gilles de Gennes]] received the Nobel Prize in Physics for developing a generalized theory of phase transitions with particular applications to describing ordering and phase transitions in polymers.<ref>{{Cite web|url=https://www.nobelprize.org/prizes/physics/1991/press-release/|title=The Nobel Prize in Physics 1991|website=/www.nobelprize.org}}</ref> Unfortunately, [[Pierre-Gilles de Gennes|de Gennes]] wrote in ''Nature'' that [[polymers]] should be distinguished from other types of [[colloid]]s, even though they can display similar clustering and [[phase separation]] behaviour,<ref>{{cite journal | vauthors = de Gennes PG | title = Ultradivided matter | journal = Nature | volume = 412 | issue = 6845 | pages = 385 | date = July 2001 | pmid = 11473291 | doi = 10.1038/35086662 | s2cid = 39983702 | bibcode = 2001Natur.412..385D | doi-access = free }}</ref> a stance that has been reflected in the reduced usage of the term [[colloid]] to describe the higher-order association behaviour of [[biopolymers]] in modern cell biology and [[molecular self-assembly]].

=== Phase separation revisited ===
Advances in [[confocal microscopy]] at the end of the 20th century identified [[proteins]], [[RNA]] or [[carbohydrates]] localising to many non-membrane bound cellular compartments within the [[cytoplasm]] or [[Cell nucleus|nucleus]] which were variously referred to as 'puncta/dots',<ref name="CliffeHamada2003">{{cite journal | vauthors = Cliffe A, Hamada F, Bienz M | title = A role of Dishevelled in relocating Axin to the plasma membrane during wingless signaling | journal = Current Biology | volume = 13 | issue = 11 | pages = 960–6 | date = May 2003 | pmid = 12781135 | doi = 10.1016/S0960-9822(03)00370-1 | s2cid = 15211115 | doi-access = free | bibcode = 2003CBio...13..960C }}</ref><ref name="Schwarz-Romond2005">{{cite journal | vauthors = Schwarz-Romond T, Merrifield C, Nichols BJ, Bienz M | title = The Wnt signalling effector Dishevelled forms dynamic protein assemblies rather than stable associations with cytoplasmic vesicles | journal = Journal of Cell Science | volume = 118 | issue = Pt 22 | pages = 5269–77 | date = November 2005 | pmid = 16263762 | doi = 10.1242/jcs.02646 | s2cid = 16988383 | doi-access =  }}</ref><ref name="Schwarz-RomondFiedler2007">{{cite journal | vauthors = Schwarz-Romond T, Fiedler M, Shibata N, Butler PJ, Kikuchi A, Higuchi Y, Bienz M | title = The DIX domain of Dishevelled confers Wnt signaling by dynamic polymerization | journal = Nature Structural & Molecular Biology | volume = 14 | issue = 6 | pages = 484–92 | date = June 2007 | pmid = 17529994 | doi = 10.1038/nsmb1247 | s2cid = 29584068 }}</ref><ref name="Schwarz-RomondMetcalfe2007">{{cite journal | vauthors = Schwarz-Romond T, Metcalfe C, Bienz M | title = Dynamic recruitment of axin by Dishevelled protein assemblies | journal = Journal of Cell Science | volume = 120 | issue = Pt 14 | pages = 2402–12 | date = July 2007 | pmid = 17606995 | doi = 10.1242/jcs.002956 | s2cid = 23270805 | doi-access =  }}</ref> '[[signalosome]]s',<ref name="BilicHuang2007">{{cite journal | vauthors = Bilic J, Huang YL, Davidson G, Zimmermann T, Cruciat CM, Bienz M, Niehrs C | title = Wnt induces LRP6 signalosomes and promotes dishevelled-dependent LRP6 phosphorylation | journal = Science | volume = 316 | issue = 5831 | pages = 1619–22 | date = June 2007 | pmid = 17569865 | doi = 10.1126/science.1137065 | s2cid = 25980578 | bibcode = 2007Sci...316.1619B }}</ref><ref name="Bienz2014">{{cite journal | vauthors = Bienz M | title = Signalosome assembly by domains undergoing dynamic head-to-tail polymerization | journal = Trends in Biochemical Sciences | volume = 39 | issue = 10 | pages = 487–95 | date = October 2014 | pmid = 25239056 | doi = 10.1016/j.tibs.2014.08.006 }}</ref> '[[stress granule|granules]]',<ref name="KedershaAnderson2002">{{cite journal | vauthors = Kedersha N, Anderson P | title = Stress granules: sites of mRNA triage that regulate mRNA stability and translatability | journal = Biochemical Society Transactions | volume = 30 | issue = Pt 6 | pages = 963–9 | date = November 2002 | pmid = 12440955 | doi = 10.1042/bst0300963 }}</ref> '[[Lewy body|bodies]]', '[[Supramolecular assembly|assemblies]]',<ref name="Schwarz-RomondMetcalfe2007"/> '[[paraspeckles]]', '[[purinosome]]s',<ref name="AnKumar2008">{{cite journal | vauthors = An S, Kumar R, Sheets ED, Benkovic SJ | title = Reversible compartmentalization of de novo purine biosynthetic complexes in living cells | journal = Science | volume = 320 | issue = 5872 | pages = 103–6 | date = April 2008 | pmid = 18388293 | doi = 10.1126/science.1152241 | s2cid = 24119538 | bibcode = 2008Sci...320..103A }}</ref> '[[cytoplasmic inclusions|inclusions]]', '[[protein aggregation|aggregates]]' or '[[Transcription factories|factories]]'. During this time period (1995-2008) the concept of [[phase separation]] was re-borrowed from [[colloid|colloidal chemistry]] & [[polymer physics]] and proposed to underlie both [[cytoplasm]]ic and [[cell nucleus|nuclear]] compartmentalization.<ref>{{cite journal | vauthors = Walter H, Brooks DE | title = Phase separation in cytoplasm, due to macromolecular crowding, is the basis for microcompartmentation | journal = FEBS Letters | volume = 361 | issue = 2–3 | pages = 135–9 | date = March 1995 | pmid = 7698310 | doi = 10.1016/0014-5793(95)00159-7 | s2cid = 8843457 | doi-access = free | bibcode = 1995FEBSL.361..135W }}</ref><ref>{{cite book | veditors=Walter H, Brooks D, Srere P | title=Microcompartmentation and Phase Separation in Cytoplasm | volume = 192 | edition = 1 | date = October 1999 | publisher = Academic Press}}</ref><ref name="Brooks1999">{{cite book| vauthors = Brooks DE |title=Microcompartmentation and Phase Separation in Cytoplasm|chapter=Can Cytoplasm Exist without Undergoing Phase Separation?|series=International Review of Cytology|volume=192|year=1999|pages=321–330|issn=0074-7696|doi=10.1016/S0074-7696(08)60532-X|pmid=10610362|isbn=9780123645968}}</ref><ref name="Walter1999">{{cite book|last1=Walter|first1=Harry|title=Microcompartmentation and Phase Separation in Cytoplasm|chapter=Consequences of Phase Separation in Cytoplasm|series=International Review of Cytology|volume=192|year=1999|pages=331–343|issn=0074-7696|doi=10.1016/S0074-7696(08)60533-1|pmid=10610363|isbn=9780123645968}}</ref><ref name="Sear1999">{{cite journal|last1=Sear|first1=Richard P.|s2cid=15005765|title=Phase behavior of a simple model of globular proteins|journal=The Journal of Chemical Physics|volume=111|issue=10|year=1999|pages=4800–4806|issn=0021-9606|doi=10.1063/1.479243|arxiv=cond-mat/9904426|bibcode=1999JChPh.111.4800S}}</ref><ref name="StradnerSedgwick2004">{{cite journal | vauthors = Stradner A, Sedgwick H, Cardinaux F, Poon WC, Egelhaaf SU, Schurtenberger P | title = Equilibrium cluster formation in concentrated protein solutions and colloids | journal = Nature | volume = 432 | issue = 7016 | pages = 492–5 | date = November 2004 | pmid = 15565151 | doi = 10.1038/nature03109 | s2cid = 4373710 | bibcode = 2004Natur.432..492S | url = http://doc.rero.ch/record/4280/files/1_schurt_ecf.pdf }}</ref><ref>{{cite journal | vauthors = Iborra FJ | title = Can visco-elastic phase separation, macromolecular crowding and colloidal physics explain nuclear organisation? | journal = Theoretical Biology & Medical Modelling | volume = 4 | issue = 15 | pages = 15 | date = April 2007 | pmid = 17430588 | pmc = 1853075 | doi = 10.1186/1742-4682-4-15 | doi-access = free }}</ref><ref name="Sear2007">{{cite journal | vauthors = Sear RP | title = Dishevelled: a protein that functions in living cells by phase separating | journal = Soft Matter | volume = 3 | issue = 6 | pages = 680–684 | date = May 2007 | pmid = 32900127 | doi = 10.1039/b618126k | bibcode = 2007SMat....3..680S }}</ref><ref name="Sear2008">{{cite journal | vauthors = Sear RP | title = Phase separation of equilibrium polymers of proteins in living cells | journal = Faraday Discussions | volume = 139 | pages = 21–34; discussion 105–28, 419–20 | year = 2008 | pmid = 19048988 | doi = 10.1039/b713076g | bibcode = 2008FaDi..139...21S }}</ref><ref>{{cite journal | vauthors = Dumetz AC, Chockla AM, Kaler EW, Lenhoff AM | title = Protein phase behavior in aqueous solutions: crystallization, liquid–liquid phase separation, gels, and aggregates | journal = Biophysical Journal | volume = 94 | issue = 2 | pages = 570–83 | date = January 2008 | pmid = 18160663 | pmc = 2157236 | doi = 10.1529/biophysj.107.116152 | bibcode = 2008BpJ....94..570D }}</ref>

Since 2009, further evidence for biomacromolecules undergoing intracellular [[phase transition]]s ([[spinodal decomposition|phase separation]]) has been observed in many different contexts, both within cells and in reconstituted ''in vitro'' experiments.<ref name=":1"/><ref>{{cite journal | vauthors = Larson AG, Elnatan D, Keenen MM, Trnka MJ, Johnston JB, Burlingame AL, Agard DA, Redding S, Narlikar GJ | display-authors = 6 | title = Liquid droplet formation by HP1α suggests a role for phase separation in heterochromatin | journal = Nature | volume = 547 | issue = 7662 | pages = 236–240 | date = July 2017 | pmid = 28636604 | pmc = 5606208 | doi = 10.1038/nature22822 | bibcode = 2017Natur.547..236L }}</ref><ref>{{cite journal | vauthors = Nott TJ, Petsalaki E, Farber P, Jervis D, Fussner E, Plochowietz A, Craggs TD, Bazett-Jones DP, Pawson T, Forman-Kay JD, Baldwin AJ | display-authors = 6 | title = Phase transition of a disordered nuage protein generates environmentally responsive membraneless organelles | journal = Molecular Cell | volume = 57 | issue = 5 | pages = 936–947 | date = March 2015 | pmid = 25747659 | pmc = 4352761 | doi = 10.1016/j.molcel.2015.01.013 }}</ref><ref>{{cite journal | vauthors = Patel A, Lee HO, Jawerth L, Maharana S, Jahnel M, Hein MY, Stoynov S, Mahamid J, Saha S, Franzmann TM, Pozniakovski A, Poser I, Maghelli N, Royer LA, Weigert M, Myers EW, Grill S, Drechsel D, Hyman AA, Alberti S | display-authors = 6 | title = A Liquid-to-Solid Phase Transition of the ALS Protein FUS Accelerated by Disease Mutation | journal = Cell | volume = 162 | issue = 5 | pages = 1066–77 | date = August 2015 | pmid = 26317470 | doi = 10.1016/j.cell.2015.07.047 | doi-access = free }}</ref><ref name="Coexisting Liquid Phases Underlie N">{{cite journal | vauthors = Feric M, Vaidya N, Harmon TS, Mitrea DM, Zhu L, Richardson TM, Kriwacki RW, Pappu RV, Brangwynne CP | display-authors = 6 | title = Coexisting Liquid Phases Underlie Nucleolar Subcompartments | journal = Cell | volume = 165 | issue = 7 | pages = 1686–1697 | date = June 2016 | pmid = 27212236 | pmc = 5127388 | doi = 10.1016/j.cell.2016.04.047 }}</ref><ref>{{Cite journal| vauthors = Riback JA, Zhu L, Ferrolino MC, Tolbert M, Mitrea DM, Sanders DW, Wei MT, Kriwacki RW, Brangwynne CP | display-authors = 6 |date=2019-10-22|title=Composition dependent phase separation underlies directional flux through the nucleolus |journal=bioRxiv|language=en|pages=809210|doi=10.1101/809210|doi-access=free}}</ref><ref name=":3">{{cite journal | vauthors = Li P, Banjade S, Cheng HC, Kim S, Chen B, Guo L, Llaguno M, Hollingsworth JV, King DS, Banani SF, Russo PS, Jiang QX, Nixon BT, Rosen MK | display-authors = 6 | title = Phase transitions in the assembly of multivalent signalling proteins | journal = Nature | volume = 483 | issue = 7389 | pages = 336–40 | date = March 2012 | pmid = 22398450 | pmc = 3343696 | doi = 10.1038/nature10879 | bibcode = 2012Natur.483..336L }}</ref>

The newly coined term "'''biomolecular condensate'''"<ref name=":2" /> refers to biological polymers (as opposed to synthetic [[polymers]]) that undergo [[self assembly]] via clustering to increase the local concentration of the assembling components, and is analogous to the physical definition of [[condensation]].<ref>{{cite journal | vauthors = Wheeler RJ, Hyman AA | title = Controlling compartmentalization by non-membrane-bound organelles | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 373 | issue = 1747 | pages = 4666–4684 | date = May 2018 | pmid = 29632271 | pmc = 5904305 | doi = 10.1098/rstb.2017.0193 }}</ref><ref name=":2">{{cite journal | vauthors = Banani SF, Lee HO, Hyman AA, Rosen MK | title = Biomolecular condensates: organizers of cellular biochemistry | journal = Nature Reviews. Molecular Cell Biology | volume = 18 | issue = 5 | pages = 285–298 | date = May 2017 | pmid = 28225081 | pmc = 7434221 | doi = 10.1038/nrm.2017.7 | s2cid = 37694361 }}</ref>

In physics, [[condensation]] typically refers to a gas–liquid [[phase transition]].

In biology the term 'condensation' is used much more broadly and can also refer to liquid–liquid [[phase separation]] to form [[colloid]]al [[emulsions]] or [[liquid crystal]]s within cells, and liquid–solid [[phase separation]] to form [[gel]]s,<ref name=":4" /> [[sol (colloid)|sols]], or [[suspension (chemistry)|suspensions]] within cells as well as liquid-to-solid [[phase transition]]s such as [[DNA condensation]] during [[prophase]] of the cell cycle or protein condensation of crystallins in [[cataract]]s.<ref name="iovs.org"/> With this in mind, the term 'biomolecular condensates' was deliberately introduced to reflect this breadth (see below). Since biomolecular condensation generally involves oligomeric or polymeric interactions between an indefinite number of components, it is generally considered distinct from formation of smaller stoichiometric protein complexes with defined numbers of subunits, such as viral capsids or the proteasome – although both are examples of spontaneous [[molecular self-assembly|molecular]] [[self-assembly]] or [[self-organisation]].

Mechanistically, it appears that the conformational landscape<ref>{{cite journal | vauthors = Garaizar A, Sanchez-Burgos I, Collepardo-Guevara R, Espinosa JR | title = Expansion of Intrinsically Disordered Proteins Increases the Range of Stability of Liquid–Liquid Phase Separation | journal = Molecules | volume = 25 | issue = 20 | pages = 4705 | date = October 2020 | pmid = 33076213 | pmc = 7587599 | doi = 10.3390/molecules25204705 | doi-access = free }}</ref> (in particular, whether it is enriched in extended disordered states) and multivalent interactions between [[intrinsically disordered proteins]] (including cross-beta polymerisation),<ref name="KatoMcKnight2017">{{cite journal | vauthors = Kato M, McKnight SL | title = Cross-β Polymerization of Low Complexity Sequence Domains | journal = Cold Spring Harbor Perspectives in Biology | volume = 9 | issue = 3 | pages = a023598 | date = March 2017 | pmid = 27836835 | pmc = 5334260 | doi = 10.1101/cshperspect.a023598 }}</ref> and/or [[protein domains]] that induce head-to-tail oligomeric or polymeric clustering,<ref name="Bienz2020">{{cite journal | vauthors = Bienz M | title = Head-to-Tail Polymerization in the Assembly of Biomolecular Condensates | journal = Cell | volume = 182 | issue = 4 | pages = 799–811 | date = August 2020 | pmid = 32822572 | doi = 10.1016/j.cell.2020.07.037 | s2cid = 221198567 | doi-access = free }}</ref> might play a role in phase separation of proteins.

== Examples ==
[[File:Stress granule dynamics.png|thumb|[[Stress granule]] dynamics]]
Many examples of biomolecular condensates have been characterized in the [[cytoplasm]] and the [[cell nucleus|nucleus]] that are thought to arise by either liquid–liquid or liquid–solid phase separation.

=== Cytoplasmic condensates ===
* [[Lewy bodies]]
* [[Stress granule]]
* [[P-body]]
* [[Oskar (gene)#P granule formation|Germline P-granules]] – [[oskar (gene)|oskar]]
* [[cytoplasmic inclusions|Starch granules]]
* [[cytoplasmic inclusions|Glycogen granules]]<ref name="NakanoTrie2014">{{cite journal | vauthors = Nakano A, Trie R, Tateishi K | title = Glycogen-Surfactant Complexes: Phase Behavior in a Water/Phytoglycogen/Sodium Dodecyl Sulfate (SDS) System | journal = Bioscience, Biotechnology, and Biochemistry | volume = 61 | issue = 12 | pages = 2063–8 | date = January 1997 | pmid = 27396883 | doi = 10.1271/bbb.61.2063 | doi-access = free }}</ref>
*Frodosomes ([[Dishevelled binding antagonist of beta catenin 1 (DACT1)|Dact1]])<ref>{{Cite journal|last1=Esposito|first1=Mark|last2=Fang|first2=Cao|last3=Cook|first3=Katelyn C.|last4=Park|first4=Nana|last5=Wei|first5=Yong|last6=Spadazzi|first6=Chiara|last7=Bracha|first7=Dan|last8=Gunaratna|first8=Ramesh T.|last9=Laevsky|first9=Gary|last10=DeCoste|first10=Christina J.|last11=Slabodkin|first11=Hannah|date=March 2021|title=TGF-β-induced DACT1 biomolecular condensates repress Wnt signalling to promote bone metastasis|journal=Nature Cell Biology|language=en|volume=23|issue=3|pages=257–267|doi=10.1038/s41556-021-00641-w|pmid=33723425|pmc=7970447|issn=1476-4679}}</ref>
* [[cornea|Corneal lens]] formation and [[cataracts]]<ref name="Observation of protein diffusivity"/><ref name="Phase separation of a protein-water"/><ref name="Cytoplasmic phase separation in for"/><ref name="ThomsonSchurtenberger1987"/><ref name="Binary-liquid phase separation of l"/><ref name="iovs.org"/>
* Other [[cytoplasmic inclusions]] such as pigment granules or cytoplasmic crystals
* Purinosomes<ref name="AnKumar2008"/>
* Misfolded [[protein aggregation]] such as [[amyloid fibrils]] or mutant Haemoglobin S (HbS) fibres in [[sickle cell disease]]
* [[Signalosome]]s, such as the [[supramolecular assemblies]] in the [[Wnt signaling pathway]].<ref name="Beta-Catenin Signaling">{{cite journal | vauthors = Schaefer KN, [[Mark Peifer|Peifer M]] | title = Wnt/Beta-Catenin Signaling Regulation and a Role for Biomolecular Condensates | journal = Developmental Cell | volume = 48 | issue = 4 | pages = 429–444 | date = February 2019 | pmid = 30782412 | pmc = 6386181 | doi = 10.1016/j.devcel.2019.01.025 }}</ref><ref name="Multiprotein complexes governing Wn">{{cite journal | vauthors = Gammons M, Bienz M | title = Multiprotein complexes governing Wnt signal transduction | journal = Current Opinion in Cell Biology | volume = 51 | issue = 1 | pages = 42–49 | date = April 2018 | pmid = 29153704 | doi = 10.1016/j.ceb.2017.10.008 }}</ref>
* It can also be argued that [[cytoskeleton|cytoskeletal filaments]] form by a polymerisation process similar to phase separation, except ordered into filamentous networks instead of amorphous droplets or granules.
*Bacteria Ribonucleoprotein Bodies (BR-bodies)- In recent studies it has been shown that bacteria RNA degradosomes can assemble into phase-separated structures, termed bacterial ribonucleoprotein bodies (BR-bodies), with many analogous properties to eukaryotic processing bodies (P-bodies) and stress granules.<ref>{{cite journal | vauthors = Muthunayake NS, Tomares DT, Childers WS, Schrader JM | title = Phase-separated bacterial ribonucleoprotein bodies organize mRNA decay | journal = Wiley Interdisciplinary Reviews. RNA | volume = 11 | issue = 6 | pages = e1599 | date = November 2020 | pmid = 32445438 | pmc = 7554086 | doi = 10.1002/wrna.1599 }}</ref>
*FLOE1 granules: FLOE1 is a prion-like seed-specific protein that controls plant seed germination via phase separation into biomolecular condensates.<ref>{{cite journal |last1=Dorone |first1=Yanniv |last2=Boeynaems |first2=Steven |last3=Jin |first3=Benjamin |last4=Bossi |first4=Flavia |last5=Flores |first5=Eduardo |last6=Lazarus |first6=Elena |last7=Michiels |first7=Emiel |last8=De Decker |first8=Mathias |last9=Baatsen |first9=Pieter |last10=Holehouse |first10=Alex S. |last11=Sukenik |first11=Shahar |last12=Gitler |first12=Aaron D. |last13=Rhee |first13=Seung Y. |s2cid=221096771 |title=A prion-like protein regulator of seed germination undergoes hydration-dependent phase separation. |journal=Cell |date=July 2021 |volume=184 |issue=16 |pages=4284–4298.e27 |doi=10.1016/j.cell.2021.06.009 |pmid=34233164 |pmc=8513799 |url=https://doi.org/10.1016/j.cell.2021.06.009}}</ref>

=== Nuclear condensates ===
[[File:Formation and examples of nuclear membraneless compartments.png|thumb|Formation and examples of [[nuclear bodies]] ]]

* [[Nucleolus]]<ref name="Coexisting Liquid Phases Underlie N"/>
* [[Nuclear speckle]]
* [[Cajal body]]
* [[Paraspeckle]]
* [[Synaptonemal complex]]
Other nuclear structures including [[heterochromatin]] form by mechanisms similar to phase separation, so can also be classified as biomolecular condensates.

=== Plasma membrane associated condensates ===
* Membrane protein, or membrane-associated protein, clustering at neurological [[synapses]], cell-cell [[tight junctions]], or other membrane domains.<ref name="CaseDitlev2019">{{cite journal | vauthors = Case LB, Ditlev JA, Rosen MK | title = Regulation of Transmembrane Signaling by Phase Separation | journal = Annual Review of Biophysics | volume = 48 | issue = 1 | pages = 465–494 | date = May 2019 | pmid = 30951647 | pmc = 6771929 | doi = 10.1146/annurev-biophys-052118-115534 }}</ref>

=== Secreted extracellular condensates ===
* Secreted [[thyroglobulin]] colloid and [[colloid nodule]]s of the [[thyroid]] gland
* Secreted [[casein]] 'micelles' of the mammary gland
* Serum [[albumin]] and [[globulins]]
* Secreted [[lysozyme]]<ref name="MuscholRosenberger1997">{{cite journal|last1=Muschol|first1=Martin|last2=Rosenberger|first2=Franz|title=Liquid–liquid phase separation in supersaturated lysozyme solutions and associated precipitate formation/crystallization|journal=The Journal of Chemical Physics|volume=107|issue=6|year=1997|pages=1953–1962|issn=0021-9606|doi=10.1063/1.474547|bibcode=1997JChPh.107.1953M}}</ref><ref name="StradnerSedgwick2004"/>

=== Lipid-enclosed organelles and [[lipoprotein]]s are not considered condensates ===
Typical [[organelles]] or [[endosomes]] enclosed by a [[lipid bilayer]] are not considered biomolecular condensates. In addition, [[lipid droplets]] are surrounded by a lipid monolayer in the cytoplasm, or in [[milk]], or in tears,<ref name="PattersonVogel2016">{{cite journal | vauthors = Patterson M, Vogel HJ, Prenner EJ | title = Biophysical characterization of monofilm model systems composed of selected tear film phospholipids | journal = Biochimica et Biophysica Acta (BBA) - Biomembranes | volume = 1858 | issue = 2 | pages = 403–14 | date = February 2016 | pmid = 26657693 | doi = 10.1016/j.bbamem.2015.11.025 | doi-access = free }}</ref> so appear to fall under the 'membrane bound' category. Finally, secreted [[LDL]] and [[High-density lipoprotein|HDL]] [[lipoprotein]] particles are also enclosed by a lipid monolayer. The formation of these structures involves [[phase separation]] to from [[colloid]]al [[micelle]]s or [[liquid crystal]] bilayers, but they are not classified as biomolecular condensates, as this term is reserved for non-membrane bound organelles.

== Liquid–liquid phase separation (LLPS) in biology ==
[[File:Biomolecular partitioning.png|thumb|Biomolecular partitioning]]

=== Liquid biomolecular condensates ===
Liquid–liquid [[phase separation]] (LLPS) generates a subtype of [[colloid]] known as an '''[[emulsions|emulsion]]''' that can [[Coalescence (physics)|coalesce]] to form large droplets within a liquid. Ordering of molecules during liquid–liquid [[phase separation]] can generate '''[[liquid crystal]]s''' rather than [[emulsions]]. In cells, LLPS produces a liquid subclass of biomolecular condensate that can behave as either an [[emulsion]] or [[liquid crystal]].

The term '''biomolecular condensates''' was introduced in the context of intracellular assemblies as a convenient but non-exclusionary term to describe non-stoichiometric assemblies of biomolecules.<ref name=":2" /> The choice of language here is specific and important. It has been proposed that many biomolecular condensates form through liquid–liquid [[phase separation]] (LLPS) to form [[colloid]]al [[emulsions]] or [[liquid crystal]]s in living organisms, as opposed to liquid–solid [[phase separation]] to form [[crystal]]s/[[protein aggregation|aggregates]] in [[gel]]s,<ref name=":4" /> [[sol (colloid)|sols]] or [[suspension (chemistry)|suspensions]] within cells or extracellular secretions.<ref name="Tang2019">{{cite journal | vauthors = Tang L | title = Optogenetic tools light up phase separation | journal = Nature Methods | volume = 16 | issue = 2 | pages = 139 | date = February 2019 | pmid = 30700901 | doi = 10.1038/s41592-019-0310-5 | s2cid = 59525729 | doi-access = free | type = Paper }}{{Subscription required}}</ref> However, unequivocally demonstrating that a cellular body forms through liquid–liquid phase separation is challenging,<ref name=":0">{{cite journal | vauthors = Hyman AA, Weber CA, Jülicher F | title = Liquid–liquid phase separation in biology | journal = Annual Review of Cell and Developmental Biology | volume = 30 | issue = 1 | pages = 39–58 | date = 2014-10-11 | pmid = 25288112 | doi = 10.1146/annurev-cellbio-100913-013325 | doi-access = free }}</ref><ref name=":1" /><ref>{{cite journal | vauthors = McSwiggen DT, Mir M, Darzacq X, Tjian R | title = Evaluating phase separation in live cells: diagnosis, caveats, and functional consequences | journal = Genes & Development | volume = 33 | issue = 23–24 | pages = 1619–1634 | date = December 2019 | pmid = 31594803 | pmc = 6942051 | doi = 10.1101/gad.331520.119 }}</ref><ref>{{cite book | vauthors = Posey AE, Holehouse AS, Pappu RV | title = Intrinsically Disordered Proteins | chapter = Phase Separation of Intrinsically Disordered Proteins | series = Methods in Enzymology | volume = 611 | pages = 1–30 | date = 2018 | pmid = 30471685 | doi = 10.1016/bs.mie.2018.09.035 | publisher = Elsevier | isbn = 978-0-12-815649-0 }}</ref> because different material states (liquid vs. gel vs. solid) are not always easy to distinguish in living cells.<ref>{{cite journal | vauthors = Woodruff JB, Hyman AA, Boke E | title = Organization and Function of Non-dynamic Biomolecular Condensates | journal = Trends in Biochemical Sciences | volume = 43 | issue = 2 | pages = 81–94 | date = February 2018 | pmid = 29258725 | doi = 10.1016/j.tibs.2017.11.005 }}</ref><ref>{{cite journal | vauthors = Boeynaems S, Alberti S, Fawzi NL, Mittag T, Polymenidou M, Rousseau F, Schymkowitz J, Shorter J, Wolozin B, Van Den Bosch L, Tompa P, Fuxreiter M | display-authors = 6 | title = Protein Phase Separation: A New Phase in Cell Biology | journal = Trends in Cell Biology | volume = 28 | issue = 6 | pages = 420–435 | date = June 2018 | pmid = 29602697 | pmc = 6034118 | doi = 10.1016/j.tcb.2018.02.004 }}</ref> The term "biomolecular condensate" directly addresses this challenge by making no assumption regarding either the physical mechanism through which assembly is achieved, nor the material state of the resulting assembly. Consequently, cellular bodies that form through liquid–liquid phase separation are a subset of biomolecular condensates, as are those where the physical origins of assembly are unknown. Historically, many cellular non-membrane bound compartments identified microscopically fall under the broad umbrella of biomolecular condensates.

In physics, phase separation can be classified into the following types of [[colloid]], of which biomolecular condensates are one example:
{| class="wikitable" style="text-align:center"
|-
! rowspan="2" colspan="2" | Medium/phase
! colspan="3" | Dispersed phase
|-
! Gas !! Liquid !! Solid
|-
! rowspan="3" | Dispersion <br />medium
! Gas
| {{unknown|No such colloids are known.<br />Helium and xenon are known to be [[Miscibility|immiscible]] under certain conditions.}}<ref name="de Swaan AronsDiepen2010">{{cite journal|last1=de Swaan Arons|first1=J.|last2=Diepen|first2=G. A. M.|title=Immiscibility of gases. The system He-Xe: (Short communication)|journal=Recueil des Travaux Chimiques des Pays-Bas|volume=82|issue=8|year=2010|pages=806|issn=0165-0513|doi=10.1002/recl.19630820810}}</ref><ref name="de Swaan AronsDiepen1996">{{Cite journal|last1=de Swaan Arons|first1=J.|last2=Diepen|first2=G. A. M.|year=1966|title=Gas—Gas Equilibria|journal=J. Chem. Phys.|volume=44|issue=6|page=2322|doi=10.1063/1.1727043|bibcode=1966JChPh..44.2322D}}</ref>
||'''Liquid [[aerosol]]'''<br />Examples: [[fog]], [[cloud]]s, [[condensation]], [[mist]], [[hair spray]]s||'''Solid aerosol'''<br />Examples: [[smoke]], [[ice cloud]], [[atmospheric particulate matter]]
|-
! Liquid
|'''[[Foam]]'''<br />Example: [[whipped cream]], [[shaving cream]], [[Gas vesicle]]s||'''[[Emulsion]] or [[Liquid crystal]]'''<br />Examples: [[milk]], [[mayonnaise]], [[lotion|hand cream]], [[latex]], [[biological membranes]], [[lipid polymorphism|micelles]], [[lipoproteins]], [[silk]], '''liquid biomolecular condensates''' ||'''[[Sol (colloid)|Sol]] or [[suspension (chemistry)|suspension]]'''<br />Examples: [[ink|pigmented ink]], [[sedimentation|sediment]], [[precipitation|precipitates]], [[protein aggregation|aggregates]], fibres/fibrils/filaments, [[crystal]]s, '''solid biomolecular condensates'''
|-
! Solid
|'''Solid foam'''<br />Examples: [[aerogel]], [[Expanded polystyrene|styrofoam]], [[pumice]]||'''[[Gel]]'''<br />Examples: [[agar]], [[gelatin]], [[Fruit preserves|jelly]], '''gel-like biomolecular condensates'''||'''Solid sol'''<br />Example: [[cranberry glass]]
|}

In biology, the most relevant forms of [[phase separation]] are either liquid–liquid or liquid–solid, although there have been reports of [[gas vesicles]] surrounded by a phase separated protein coat in the cytoplasm of some microorganisms.<ref name="BayroDaviso2012">{{cite journal | vauthors = Bayro MJ, Daviso E, Belenky M, Griffin RG, Herzfeld J | title = An amyloid organelle, solid-state NMR evidence for cross-β assembly of gas vesicles | journal = The Journal of Biological Chemistry | volume = 287 | issue = 5 | pages = 3479–84 | date = January 2012 | pmid = 22147705 | pmc = 3271001 | doi = 10.1074/jbc.M111.313049 | doi-access = free }}</ref>

=== Wnt signalling ===
One of the first discovered examples of a highly dynamic intracellular '''liquid biomolecular condensate''' with a clear physiological function were the supramolecular complexes ('''Wnt [[signalosome]]s''') formed by components of the [[Wnt signaling pathway]].<ref name="Sear2007"/><ref name="Beta-Catenin Signaling" /><ref name="Multiprotein complexes governing Wn"/> The [[Dishevelled]] (Dsh or Dvl) protein undergoes clustering in the cytoplasm via its DIX domain, which mediates protein clustering (polymerisation) and phase separation, and is important for signal transduction.<ref name="CliffeHamada2003"/><ref name="Schwarz-Romond2005"/><ref name="Schwarz-RomondFiedler2007"/><ref name="Schwarz-RomondMetcalfe2007"/><ref name="Bienz2014"/><ref name="Sear2007"/> The Dsh protein functions both in planar polarity and Wnt signalling, where it recruits another supramolecular complex (the Axin complex) to Wnt receptors at the plasma membrane. The formation of these Dishevelled and Axin containing droplets is conserved across metazoans, including in ''[[Drosophila]]'', ''[[Xenopus]]'', and human cells.

=== P granules ===
Another example of liquid droplets in cells are the germline P granules in ''[[Caenorhabditis elegans]]''.<ref name="Tang2019" /><ref name=":1">{{cite journal | vauthors = Brangwynne CP, Eckmann CR, Courson DS, Rybarska A, Hoege C, Gharakhani J, Jülicher F, Hyman AA | display-authors = 6 | title = Germline P granules are liquid droplets that localize by controlled dissolution/condensation | journal = Science | volume = 324 | issue = 5935 | pages = 1729–32 | date = June 2009 | pmid = 19460965 | doi = 10.1126/science.1172046 | s2cid = 42229928 | bibcode = 2009Sci...324.1729B | doi-access = free }}</ref> These granules separate out from the cytoplasm and form droplets, as oil does from water. Both the granules and the surrounding cytoplasm are liquid in the sense that they flow in response to forces, and two of the granules can coalesce when they come in contact. When (some of) the molecules in the granules are studied (via [[fluorescence recovery after photobleaching]]), they are found to rapidly turnover in the droplets, meaning that molecules diffuse into and out of the granules, just as expected in a [[liquid]] droplet. The droplets can also grow to be many molecules across (micrometres)<ref name=":1" /> Studies of droplets of the ''[[Caenorhabditis elegans]]'' protein LAF-1 ''in vitro''<ref>{{cite journal | vauthors = Elbaum-Garfinkle S, Kim Y, Szczepaniak K, Chen CC, Eckmann CR, Myong S, Brangwynne CP | title = The disordered P granule protein LAF-1 drives phase separation into droplets with tunable viscosity and dynamics | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 112 | issue = 23 | pages = 7189–94 | date = June 2015 | pmid = 26015579 | pmc = 4466716 | doi = 10.1073/pnas.1504822112 | doi-access = free | bibcode = 2015PNAS..112.7189E }}</ref> also show liquid-like behaviour, with an apparent [[viscosity]] <math>\eta \sim 10</math>Pa s. This is about a ten thousand times that of water at room temperature, but it is small enough to enable the LAF-1 droplets to flow like a liquid. Generally, interaction strength ([[Affinity (biochemistry)|affinity]])<ref>{{cite journal | vauthors = Heidenreich M, Georgeson JM, Locatelli E, Rovigatti L, Nandi SK, Steinberg A, Nadav Y, Shimoni E, Safran SA, Doye JP, Levy ED | display-authors = 6 | title = Designer protein assemblies with tunable phase diagrams in living cells | journal = Nature Chemical Biology | volume = 16 | issue = 9 | pages = 939–945 | date = September 2020 | pmid = 32661377 | doi = 10.1038/s41589-020-0576-z | hdl-access = free | first10 = Jonathan P. K. | s2cid = 220507058 | hdl = 11573/1435875 }}</ref> and valence (number of binding sites)<ref name=":3" /> of the phase separating biomolecules influence their condensates viscosity, as well as their overall tendency to phase separate.

== Liquid–liquid phase separation in human disease ==
Growing evidence suggests that anomalies in biomolecular condensates formation can lead to a number of human pathologies<ref>{{cite journal | vauthors = Aguzzi A, Altmeyer M | title = Phase Separation: Linking Cellular Compartmentalization to Disease | journal = Trends in Cell Biology | volume = 26 | issue = 7 | pages = 547–558 | date = July 2016 | pmid = 27051975 | doi = 10.1016/j.tcb.2016.03.004 }}</ref> such as cancer and [[Neurodegenerative Diseases|neurodegenerative diseases]].<ref>{{cite journal | vauthors = Shin Y, Brangwynne CP | title = Liquid phase condensation in cell physiology and disease | journal = Science | volume = 357 | issue = 6357 | pages = eaaf4382 | date = September 2017 | pmid = 28935776 | doi = 10.1126/science.aaf4382 | s2cid = 3693853 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Alberti S, Hyman AA | title = Are aberrant phase transitions a driver of cellular aging? | journal = BioEssays | volume = 38 | issue = 10 | pages = 959–68 | date = October 2016 | pmid = 27554449 | pmc = 5108435 | doi = 10.1002/bies.201600042 }}</ref>

== Biomolecular condensates in plants ==
Biomolecular condensates can play other roles in plants besides the compartmentalization of biochemical processes.<ref>{{Cite journal |last1=Emenecker |first1=Ryan J. |last2=Holehouse |first2=Alex S. |last3=Strader |first3=Lucia C. |date=2021-06-17 |title=Biological Phase Separation and Biomolecular Condensates in Plants |journal=Annual Review of Plant Biology |language=en |volume=72 |pages=17–46 |doi=10.1146/annurev-arplant-081720-015238 |issn=1543-5008 |pmc=8221409 |pmid=33684296}}</ref> They can integrate environmental cues and modulate plant development in response,<ref>{{Cite journal |last1=Field |first1=Sterling |last2=Jang |first2=Geng-Jen |last3=Dean |first3=Caroline |last4=Strader |first4=Lucia C |last5=Rhee |first5=Seung Y |date=2023-09-01 |title=Plants use molecular mechanisms mediated by biomolecular condensates to integrate environmental cues with development |url=https://academic.oup.com/plcell/article/35/9/3173/7069846 |journal=The Plant Cell |volume=35 |issue=9 |pages=3173–3186 |doi=10.1093/plcell/koad062 |issn=1040-4651 |pmc=10473230 |pmid=36879427}}</ref> influencing processes like floral transition.<ref>{{Cite journal |last1=Huang |first1=Xiaozhen |last2=Yang |first2=Yongfang |last3=Xu |first3=Cao |date=2025 |title=Biomolecular condensation programs floral transition to orchestrate flowering time and inflorescence architecture |url=https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.20204 |journal=New Phytologist |language=en |volume=245 |issue=1 |pages=88–94 |doi=10.1111/nph.20204 |pmid=39425452 |bibcode=2025NewPh.245...88H |issn=1469-8137}}</ref> They achieve this by sequestering interacting components, enhancing dwell time, and interacting with cytoplasmic properties in response to environmental changes. They have shown to be involved also in [[autophagy]],<ref>{{Cite journal |last1=Li |first1=Ruixi |last2=Pang |first2=Lei |date=2024-12-01 |title=An interplay between biomolecular condensates and SNARE proteins regulates plant autophagy |journal=Autophagy |volume=20 |issue=12 |pages=2833–2835 |doi=10.1080/15548627.2024.2408188 |issn=1554-8627 |pmc=11587832 |pmid=39324495|pmc-embargo-date=September 26, 2025 }}</ref> [[RNA silencing]],<ref>{{Cite journal |last1=Li |first1=Qi |last2=Liu |first2=Yang |last3=Zhang |first3=Xiaoming |date=2024-02-01 |title=Biomolecular condensates in plant RNA silencing: insights into formation, function, and stress responses |url=https://academic.oup.com/plcell/article/36/2/227/7286296 |journal=The Plant Cell |volume=36 |issue=2 |pages=227–245 |doi=10.1093/plcell/koad254 |issn=1040-4651 |pmc=10827315 |pmid=37772963}}</ref><ref>{{Cite journal |last1=Taliansky |first1=Michael E |last2=Love |first2=Andrew J |last3=Kołowerzo-Lubnau |first3=Agnieszka |last4=Smoliński |first4=Dariusz Jan |date=2023-09-01 |title=Cajal bodies: Evolutionarily conserved nuclear biomolecular condensates with properties unique to plants |url=https://academic.oup.com/plcell/article/35/9/3214/7172648 |journal=The Plant Cell |volume=35 |issue=9 |pages=3214–3235 |doi=10.1093/plcell/koad140 |issn=1040-4651 |pmc=10473218 |pmid=37202374}}</ref> and plant immunity.<ref>{{Cite journal |last1=Wang |first1=Wei |last2=Gu |first2=Yangnan |date=2022-04-26 |title=The emerging role of biomolecular condensates in plant immunity |url=https://academic.oup.com/plcell/article/34/5/1568/6380147 |journal=The Plant Cell |language=en |volume=34 |issue=5 |pages=1568–1572 |doi=10.1093/plcell/koab240 |pmid=34599333 |pmc=9048959 |issn=1040-4651}}</ref>

NAtural [[Deep eutectic solvent|Deep Eutectic Solvents]] (NADES) are mixtures of natural compounds such as amino acids, sugars, choline, and organic acids that can solubilize high amounts of natural products. NADES are hypothesized to be the third liquid phase in plants, due to their presence in plant cells together with their ability to improve and stabilise enzymatic reactions, as well as enhance extraction and dissolution of natural products.<ref>{{Cite journal |last1=Cajnko |first1=Miša Mojca |last2=Vicente |first2=Filipa A. |last3=Novak |first3=Uroš |last4=Likozar |first4=Blaž |date=2023 |title=Natural deep eutectic solvents (NaDES): translating cell biology to processing |url=https://xlink.rsc.org/?DOI=D3GC01913F |journal=Green Chemistry |language=en |volume=25 |issue=22 |pages=9045–9062 |doi=10.1039/D3GC01913F |issn=1463-9262|hdl=20.500.12556/DiRROS-17298 |hdl-access=free }}</ref> They are speculated to facilitate the formation of phase-separated inclusions, aiding in the storage and transport of specific metabolites<ref name=":5">{{Citation |last1=Møller |first1=Birger Lindberg |title=Chapter Eight - Metabolons and bio-condensates: The essence of plant plasticity and the key elements in development of green production systems |date=2021-01-01 |work=Advances in Botanical Research |volume=97 |pages=185–223 |editor-last=Verpoorte |editor-first=Robert |url=https://linkinghub.elsevier.com/retrieve/pii/S0065229620300495 |access-date=2025-01-24 |series=Eutectic Solvents and Stress in Plants |publisher=Academic Press |doi=10.1016/bs.abr.2020.09.006 |last2=Laursen |first2=Tomas |editor2-last=Witkamp |editor2-first=Geert-Jan |editor3-last=Choi |editor3-first=Young Hae}}</ref> such as [[anthocyanin]]s,<ref>{{Cite journal |last1=Buhrman |first1=Kees |last2=Aravena-Calvo |first2=Javiera |last3=Ross Zaulich |first3=Clara |last4=Hinz |first4=Kasper |last5=Laursen |first5=Tomas |date=2022-06-28 |title=Anthocyanic Vacuolar Inclusions: From Biosynthesis to Storage and Possible Applications |journal=Frontiers in Chemistry |language=English |volume=10 |doi=10.3389/fchem.2022.913324 |doi-access=free |issn=2296-2646 |pmc=9273883 |pmid=35836677|bibcode=2022FrCh...10.3324B }}</ref> [[dhurrin]],<ref>{{Cite journal |last1=Knudsen |first1=Camilla |last2=Bavishi |first2=Krutika |last3=Viborg |first3=Ketil Mathiasen |last4=Drew |first4=Damian Paul |last5=Simonsen |first5=Henrik Toft |last6=Motawia |first6=Mohammed Saddik |last7=Møller |first7=Birger Lindberg |last8=Laursen |first8=Tomas |date=2020-02-01 |title=Stabilization of dhurrin biosynthetic enzymes from Sorghum bicolor using a natural deep eutectic solvent |url=https://linkinghub.elsevier.com/retrieve/pii/S0031942219308040 |journal=Phytochemistry |volume=170 |pages=112214 |doi=10.1016/j.phytochem.2019.112214 |pmid=31794881 |bibcode=2020PChem.170k2214K |issn=0031-9422|doi-access=free }}</ref> and [[vanillin]].<ref name=":5" />

== Synthetic biomolecular condensates ==
Biomolecular condensates can be [[synthetic biology|synthesized]] for a number of purposes. Synthetic biomolecular condensates are inspired by [[Endogeny (biology)|endogenous]] biomolecular condensates, such as [[Nucleolin|nucleoli]], [[P-bodies|P bodies]], and [[stress granule]]s, which are essential to normal [[Cellular organizational structure|cellular organization and function]].<ref>P. Ivanov, N.  Kedersha, and P. Anderson, “Stress granules and processing bodies in translational control,” Cold Spring Harbor Perspectives in Biology, vol. 11, no. 5, 2019.</ref><ref>C. P. Brangwynne, T. J. Mitchison, and A. A. Hyman, “Active liquid-like behavior of nucleoli determines their size and shape in Xenopus laevis oocytes,” Proceedings of the National Academy of Sciences of the United States of America, vol. 108, no. 11, pp. 4334–4339, 2011.</ref>

Synthetic condensates are an important tool in [[synthetic biology]], and have a wide and growing range of applications. Engineered synthetic condensates allow for probing cellular organization, and enable the creation of novel functionalized biological materials, which have the potential to serve as [[drug delivery]] platforms and [[therapeutic agents]].<ref>D. Bracha, M. T. Walls, and C. P. Brangwynne, “Probing and engineering liquid-phase organelles,” Nature Biotechnology, vol. 37, no. 12, pp. 1435–1445, 2019.
</ref>

=== Design and control ===
Despite the dynamic nature and lack of [[Chemical specificity|binding specificity]] that govern the formation of biomolecular condensates, synthetic condensates can still be engineered to exhibit different behaviors. One popular way to conceptualize condensate interactions and aid in design is through the "sticker-spacer" framework.<ref>{{cite journal|last1=Choi|first1=J.M.|last2=Dar|first2=F.|last3=Pappu|first3=R.V.|title=LASSI: A lattice model for simulating phase transitions of multivalent proteins|journal=PLOS Computational Biology|volume=15|year=2019|issue=10 |pages=e1007028 |doi=10.1371/journal.pcbi.1007028|pmid=31634364 |pmc=6822780 |bibcode=2019PLSCB..15E7028C |doi-access=free }}</ref> Multivalent interaction sites, or "stickers", are separated by "spacers", which provide the [[Conformational ensembles|conformational]] flexibility and physically separate individual interaction modules from one another. Proteins regions identified as 'stickers' usually consist of [[Intrinsically disordered proteins|Intrinsically Disordered Regions (IDRs)]] that act as "sticky" [[biopolymer]]s via short patches of interacting residues patterned along their unstructured chain, which collectively promote [[liquid–liquid phase separation sequence-based predictors|LLPS]].<ref>{{cite journal|first1=R.L.|last1=Hastings|first2=S.|last2=Boeynaems|title=Designer Condensates: A Toolkit for the Biomolecular Architect|journal=Journal of Molecular Biology|volume=433|page=166837|date=June 2021|issue=12 |doi=10.1016/j.jmb.2021.166837|pmid=33539874 |s2cid=231819801 |doi-access=free}}</ref> By modifying the sticker-spacer framework, i.e. the [[Peptide|polypeptide]] and RNA sequences as well as their mixture compositions, the material properties ([[Viscosity|viscous]] and [[Elasticity (physics)|elastic]] regimes) of condensates can be tuned to design novel condensates.<ref>{{cite journal|first1=R.|last1=Tejedor|first2=A.|last2=Garaizar|first3=J.|last3=Ramı|title=RNA modulation of transport properties and stability in phase-separated condensates|journal=Biophysical Journal|volume=120|number=23|date=December 2021|pages=5169–5186|doi=10.1016/j.bpj.2021.11.003|pmid=34762868 |pmc=8715277 |bibcode=2021BpJ...120.5169T }}</ref>

Other tools outside of tuning the sticker-spacer framework can be used to give new functionality and to allow for high temporal and spatial control over synthetic condensates. One way to gain temporal control over the formation and [[Dissolution (chemistry)|dissolution]] of biomolecular condensates is by using [[Optogenetics|optogenetic]] tools. Several different systems have been developed which allow for control of condensate formation and dissolution which rely on [[Chimeric gene|chimeric]] [[Protein production|protein expression]], and light or small molecule activation.<ref>C. D. Reinkemeier and E. A. Lemke, “Synthetic biomolecular condensates to engineer eukaryotic cells,” Current Opinion in Chemical Biology, vol. 64, pp. 174–181, 2021.</ref> In one system,<ref>D. Bracha, M. T. Walls, M. T. Wei, L. Zhu, M. Kurian, J. L. Avalos, J. E. Toettcher, and C. P. Brangwynne, “Mapping Local and Global Liquid Phase Behavior in Living Cells Using Photo-Oligomerizable Seeds,” Cell, vol. 175, no. 6, pp. 1467–1480.e13, 2018.</ref> proteins are expressed in a [[Cell (biology)|cell]] which contain light-activated [[oligomer]]ization domains fused to IDRs. Upon irradiation with a specific [[wavelength of light]], the oligomerization domains bind each other and form a 'core', which also brings multiple IDRs close together because they are fused to the oligomerization domains. The recruitment of multiple IDRs effectively creates a new biopolymer with increased [[Valence (chemistry)|valency]]. This increased valency allows for the IDRs to form multivalent interactions and trigger [[liquid–liquid phase separation sequence-based predictors|LLPS]]. When the activation light is stopped, the oligomerization domains disassemble, causing the dissolution of the condensate. A similar system<ref>H. Zhang, C. Aonbangkhen, E. V. Tarasovetc, E. R. Ballister, D. M.Chenoweth, and M. A. Lampson, “Optogenetic control of kinetochore function,” Nature Chemical Biology, vol. 13, pp. 1096–1101, Aug 2017.</ref> achieves the same temporal control of condensate formation by using light-sensitive 'caged' [[Dimer (chemistry)|dimerizers]]. In this case, light-activation removes the dimerizer cage, allowing it to recruit IDRs to multivalent cores, which then triggers phase separation. Light-activation of a different wavelength results in the dimerizer being cleaved, which then releases the IDRs from the core and consequentially dissolves the condensate. This dimerizer system requires significantly reduced amounts of [[Laser|laser light]] to operate, which is advantageous because high intensity light can be toxic to cells.

[[Optogenetics|Optogenetic]] systems can also be modified to gain spatial control over the formation of condensates. Multiple approaches have been developed to do so. In one approach,<ref name="Y. Shin">Y. Shin, Y. C. Chang, D. S. Lee, J. Berry, D. W. Sanders, P. Ronceray, N. S.Wingreen, M. Haataja, and C. P. Brangwynne, “Liquid Nuclear Condensates Mechanically Sense and Restructure the Genome,” Cell, vol. 175, no. 6,pp. 1481–1491.e13, 2018.</ref> which localizes condensates to specific [[Genome|genomic regions]], core proteins are fused to proteins such as TRF1 or catalytically dead [[Cas9]], which bind specific genomic loci. When [[oligomer]]ization is trigger by light activation, phase separation is preferentially induced on the specific genomic region which is recognized by fusion protein. Because condensates of the same composition can interact and fuse with each other, if they are tethered to specific regions of the [[genome]], condensates can be used to alter the spatial organization of the genome, which can have effects on gene expression.<ref name="Y. Shin" />

=== As biochemical reactors ===
Synthetic condensates offer a way to probe cellular function and organization with high spatial and temporal control, but can also be used to modify or add functionality to the [[Cell (biology)|cell]]. One way this is accomplished is by modifying the [[Condensation polymer|condensate]] networks to include [[binding site]]s for other [[protein]]s of interest, thus allowing the condensate to serve as a scaffold for protein release or recruitment.<ref name="M. Yoshikawa">M. Yoshikawa and S. Tsukiji, “Modularly Built Synthetic Membraneless Organelles Enabling Targeted Protein Sequestration and Release,” Biochemistry, Oct 2021.</ref> These binding sites can be modified to be sensitive to light activation or small molecule addition, thus giving temporal control over the recruitment of a specific protein of interest. By recruiting specific proteins to condensates, [[reactants]] can be concentrated to increase [[reaction rate]]s or sequestered to inhibit reactivity.<ref>Y. Shin and C. P. Brangwynne, “Liquid phase condensation in cell physiology and disease,” Science, vol. 357, Sep 2017.</ref> In addition to protein recruitment, condensates can also be designed which release proteins in response to certain stimuli. In this case, a protein of interest can be fused to a [[scaffold protein]] via a photocleavable linker. Upon [[irradiation]], the linker is broken, and the protein is released from the condensate. Using these design principles, proteins can either be released to, or sequestered from, their native environment, allowing condensates to serve as a tool to alter the [[biochemical]] activity of specific proteins with a high level of control.<ref name="M. Yoshikawa" />

== Methods to study condensates ==
A number of experimental and computational methods have been developed to examine the physico-chemical properties and underlying molecular interactions of biomolecular condensates. Experimental approaches include phase separation assays using [[Bright-field microscopy|bright-field]] imaging or [[fluorescence microscopy]], and [[fluorescence recovery after photobleaching]] (FRAP), as well as [[Rheology|rheological]] analysis of phase-separated droplets.<ref>{{Cite journal |last1=Ganser |first1=Laura R. |last2=Myong |first2=Sua |date=2020 |title=Methods to Study Phase-Separated Condensates and the Underlying Molecular Interactions |url=https://doi.org/10.1016/j.tibs.2020.05.011 |journal=Trends in Biochemical Sciences |volume=45 |issue=11 |pages=1004–1005 |doi=10.1016/j.tibs.2020.05.011 |pmc=7697221 |pmid=32561165}}</ref> Computational approaches include coarse-grained molecular dynamics simulations and [[circuit topology]] analysis.<ref>{{Cite journal |last1=Heidari |first1=Maziar |last2=Moes |first2=Duane |last3=Schullian |first3=Otto |last4=Scalvini |first4=Barbara |last5=Mashaghi |first5=Alireza |date=2022 |title=A topology framework for macromolecular complexes and condensates |journal=Nano Research |language=en |volume=15 |issue=11 |pages=9809–9817 |doi=10.1007/s12274-022-4355-x|bibcode=2022NaRes..15.9809H |doi-access=free }}</ref>

=== Coarse-grained molecular models ===
[[Molecular dynamics]] and [[Monte Carlo simulations]] have been extensively used to gain insights into the formation and the material properties of biomolecular condensates.<ref name="SaarQianGood2023">{{cite journal | last1 = Saar | first1 = Kadi L. | last2 = Qian | first2 = Daoyuan | last3 = Good | first3 = Lydia L. | last4 = Morgunov | first4 = Alexey S. | last5 = Collepardo-Guevara | first5 = Rosana | last6 = Best | first6 = Robert B. | last7 = Knowles | first7 = Tuomas P. J. | title = Theoretical and Data-Driven Approaches for Biomolecular Condensates | journal = Chemical Reviews | date = 12 May 2023 | volume = 123 | issue = 14 | pages = 8988–9009 | issn = 0009-2665 | eissn = 1520-6890 | doi = 10.1021/acs.chemrev.2c00586 | pmid = 37171907 | url = | pmc = 10375482 }}</ref> Although molecular models of different resolution have been employed,<ref name="PaloniBaillyCiandrini2020">{{cite journal | last1 = Paloni | first1 = Matteo | last2 = Bailly | first2 = Rémy | last3 = Ciandrini | first3 = Luca | last4 = Barducci | first4 = Alessandro | title = Unraveling Molecular Interactions in Liquid–Liquid Phase Separation of Disordered Proteins by Atomistic Simulations | journal = The Journal of Physical Chemistry B | date = 16 September 2020 | volume = 124 | issue = 41 | pages = 9009–9016 | issn = 1520-6106 | eissn = 1520-5207 | doi = 10.1021/acs.jpcb.0c06288 | pmid = 32936641 | url = | doi-access = free }}</ref><ref name="Benayadvon BülowStelzl2020">{{cite journal | last1 = Benayad | first1 = Zakarya | last2 = von Bülow | first2 = Sören | last3 = Stelzl | first3 = Lukas S. | last4 = Hummer | first4 = Gerhard | title = Simulation of FUS Protein Condensates with an Adapted Coarse-Grained Model | journal = Journal of Chemical Theory and Computation | date = 14 December 2020 | volume = 17 | issue = 1 | pages = 525–537 | issn = 1549-9618 | eissn = 1549-9626 | doi = 10.1021/acs.jctc.0c01064 | pmid = 33307683 | pmc = 7872324 | url = }}</ref><ref name="EspinosaJosephSanchez-Burgos2020">{{cite journal | last1 = Espinosa | first1 = Jorge R. | last2 = Joseph | first2 = Jerelle A. | last3 = Sanchez-Burgos | first3 = Ignacio | last4 = Garaizar | first4 = Adiran | last5 = Frenkel | first5 = Daan | last6 = Collepardo-Guevara | first6 = Rosana | title = Liquid network connectivity regulates the stability and composition of biomolecular condensates with many components | journal = Proceedings of the National Academy of Sciences | date = June 2020 | volume = 117 | issue = 24 | pages = 13238–13247 | issn = 0027-8424 | eissn = 1091-6490 | doi = 10.1073/pnas.1917569117 | pmid = 32482873 | pmc = 7306995 | bibcode = 2020PNAS..11713238E | url =  | doi-access = free }}</ref> modelling efforts have mainly focused on coarse-grained models of intrinsically disordered proteins, wherein amino acid residues are represented by single interaction sites. 
Compared to more detailed molecular descriptions, residue-level models provide high computational efficiency, which enables simulations to cover the long length and time scales required to study phase separation. Moreover, the resolution of these models is sufficiently detailed to capture the dependence on amino acid sequence of the properties of the system.<ref name="SaarQianGood2023"/>

Several residue-level models of intrinsically disordered proteins have been developed in recent years. Their common features are (i) the absence of an explicit representation of solvent molecules and salt ions, (ii) a mean-field description of the electrostatic interactions between charged residues (see [[Debye–Hückel theory]]), and (iii) a set of "stickiness" parameters which quantify the strength of the attraction between pairs of amino acids. In the development of most residue-level models, the stickiness parameters have been derived from [[hydrophobicity scales]]<ref name="DignonZhengKim2018">{{cite journal | last1 = Dignon | first1 = Gregory L. | last2 = Zheng | first2 = Wenwei | last3 = Kim | first3 = Young C. | last4 = Best | first4 = Robert B. | last5 = Mittal | first5 = Jeetain | title = Sequence determinants of protein phase behavior from a coarse-grained model | journal = PLOS Computational Biology | date = 24 January 2018 | volume = 14 | issue = 1 | page = e1005941 | eissn = 1553-7358 | doi = 10.1371/journal.pcbi.1005941 | pmid = 29364893 | pmc = 5798848 | bibcode = 2018PLSCB..14E5941D | url =  | doi-access = free }}</ref> or from a bioinformatic analysis of crystal structures of folded proteins.<ref name="VernonChongTsang2018">{{cite journal | last1 = Vernon | first1 = Robert McCoy | last2 = Chong | first2 = Paul Andrew | last3 = Tsang | first3 = Brian | last4 = Kim | first4 = Tae Hun | last5 = Bah | first5 = Alaji | last6 = Farber | first6 = Patrick | last7 = Lin | first7 = Hong | last8 = Forman-Kay | first8 = Julie Deborah | title = Pi-Pi contacts are an overlooked protein feature relevant to phase separation | journal = eLife | date = 9 February 2018 | volume = 7 | eissn = 2050-084X | doi = 10.7554/eLife.31486 | pmid = 29424691 | pmc = 5847340 | url =  | doi-access = free }}</ref><ref name="JosephReinhardtAguirre2021">{{cite journal | last1 = Joseph | first1 = Jerelle A. | last2 = Reinhardt | first2 = Aleks | last3 = Aguirre | first3 = Anne | last4 = Chew | first4 = Pin Yu | last5 = Russell | first5 = Kieran O. | last6 = Espinosa | first6 = Jorge R. | last7 = Garaizar | first7 = Adiran | last8 = Collepardo-Guevara | first8 = Rosana | title = Physics-driven coarse-grained model for biomolecular phase separation with near-quantitative accuracy | journal = Nature Computational Science | date = 22 November 2021 | volume = 1 | issue = 11 | pages = 732–743 | eissn = 2662-8457 | doi = 10.1038/s43588-021-00155-3 | pmid = 35795820 | pmc = 7612994 | url = }}</ref> Further refinement of the parameters has been achieved through iterative procedures which maximize the agreement between model predictions and a set of experiments,<ref name="RegyThompsonKim2021">{{cite journal | last1 = Regy | first1 = Roshan Mammen | last2 = Thompson | first2 = Jacob | last3 = Kim | first3 = Young C. | last4 = Mittal | first4 = Jeetain | title = Improved coarse-grained model for studying sequence dependent phase separation of disordered proteins | journal = Protein Science | date = 24 May 2021 | volume = 30 | issue = 7 | pages = 1371–1379 | issn = 0961-8368 | eissn = 1469-896X | doi = 10.1002/pro.4094 | pmid = 33934416 | pmc = 8197430 | url = }}</ref><ref name="Dannenhoffer-LafageBest2021">{{cite journal | last1 = Dannenhoffer-Lafage | first1 = Thomas | last2 = Best | first2 = Robert B. | title = A Data-Driven Hydrophobicity Scale for Predicting Liquid–Liquid Phase Separation of Proteins | journal = The Journal of Physical Chemistry B | date = 20 April 2021 | volume = 125 | issue = 16 | pages = 4046–4056 | issn = 1520-6106 | eissn = 1520-5207 | doi = 10.1021/acs.jpcb.0c11479 | pmid = 33876938 | s2cid = 233309675 | url = }}</ref><ref name="LathamZhang2021">{{cite journal | last1 = Latham | first1 = Andrew P. | last2 = Zhang | first2 = Bin | title = Consistent Force Field Captures Homologue-Resolved HP1 Phase Separation | journal = Journal of Chemical Theory and Computation | date = 7 April 2021 | volume = 17 | issue = 5 | pages = 3134–3144 | issn = 1549-9618 | eissn = 1549-9626 | doi = 10.1021/acs.jctc.0c01220 | pmid = 33826337 | pmc = 8119372 | url = }}</ref><ref name="TeseiSchulzeCrehuet2021">{{cite journal | last1 = Tesei | first1 = Giulio | last2 = Schulze | first2 = Thea K. | last3 = Crehuet | first3 = Ramon | last4 = Lindorff-Larsen | first4 = Kresten | title = Accurate model of liquid–liquid phase behavior of intrinsically disordered proteins from optimization of single-chain properties | journal = Proceedings of the National Academy of Sciences | date = 29 October 2021 | volume = 118 | issue = 44 | issn = 0027-8424 | eissn = 1091-6490 | doi = 10.1073/pnas.2111696118 | pmid = 34716273 | pmc = 8612223 | bibcode = 2021PNAS..11811696T | url =  | doi-access = free }}</ref><ref name="FaragCohenBorcherds2022">{{cite journal | last1 = Farag | first1 = Mina | last2 = Cohen | first2 = Samuel R. | last3 = Borcherds | first3 = Wade M. | last4 = Bremer | first4 = Anne | last5 = Mittag | first5 = Tanja | last6 = Pappu | first6 = Rohit V. | title = Condensates formed by prion-like low-complexity domains have small-world network structures and interfaces defined by expanded conformations | journal = Nature Communications | date = 13 December 2022 | volume = 13 | issue = 1 | page = 7722 | eissn = 2041-1723 | doi = 10.1038/s41467-022-35370-7 | pmid = 36513655 | pmc = 9748015 | bibcode = 2022NatCo..13.7722F | url = }}</ref><ref name="Valdes-GarciaHeoLapidus2023">{{cite journal | last1 = Valdes-Garcia | first1 = Gilberto | last2 = Heo | first2 = Lim | last3 = Lapidus | first3 = Lisa J. | last4 = Feig | first4 = Michael | title = Modeling Concentration-dependent Phase Separation Processes Involving Peptides and RNA via Residue-Based Coarse-Graining | journal = Journal of Chemical Theory and Computation | date = 6 January 2023 | volume = 19 | issue = 2 | pages = 669–678 | issn = 1549-9618 | eissn = 1549-9626 | doi = 10.1021/acs.jctc.2c00856 | pmid = 36607820 | pmc = 10323037 | url =  }}</ref> or by leveraging data obtained from all-atom molecular dynamics simulations.<ref name="JosephReinhardtAguirre2021"/>

Residue-level models of intrinsically disordered proteins have been validated by direct comparison with experimental data, and their predictions have been shown to be accurate across diverse amino acid sequences.<ref name="RegyThompsonKim2021"/><ref name="Dannenhoffer-LafageBest2021"/><ref name="LathamZhang2021"/><ref name="JosephReinhardtAguirre2021"/><ref name="FaragCohenBorcherds2022"/><ref name="TeseiLindorff-Larsen2023">{{cite journal | last1 = Tesei | first1 = Giulio | last2 = Lindorff-Larsen | first2 = Kresten | title = Improved predictions of phase behaviour of intrinsically disordered proteins by tuning the interaction range | journal = Open Research Europe | date = 17 January 2023 | volume = 2 | page = 94 | eissn = 2732-5121 | doi = 10.12688/openreseurope.14967.2 | pmid = 37645312| pmc = 10450847 | url = | doi-access = free }}</ref><ref name="Valdes-GarciaHeoLapidus2023"/> Examples of experimental data used to validate the models are [[radius of gyration|radii of gyration]] of isolated chains and [[saturation concentration]]s, which are threshold protein concentrations above which phase separation is observed.<ref name="MittagPappu2022">{{cite journal |last1=Mittag |first1=Tanja |last2=Pappu |first2=Rohit V. |date=June 2022 |title=A conceptual framework for understanding phase separation and addressing open questions and challenges |url=https://pubag.nal.usda.gov/catalog/7806056 |journal=Molecular Cell |volume=82 |issue=12 |pages=2201–2214 |doi=10.1016/j.molcel.2022.05.018 |issn=1097-2765 |pmid=35675815 |s2cid=249488875|pmc=9233049 }}</ref>

Although intrinsically disordered proteins often play important roles in condensate formation,<ref name="BorcherdsBremerBorgia2021">{{cite journal | last1 = Borcherds | first1 = Wade | last2 = Bremer | first2 = Anne | last3 = Borgia | first3 = Madeleine B | last4 = Mittag | first4 = Tanja | title = How do intrinsically disordered protein regions encode a driving force for liquid–liquid phase separation? | journal = Current Opinion in Structural Biology | date = April 2021 | volume = 67 | pages = 41–50 | issn = 0959-440X | doi = 10.1016/j.sbi.2020.09.004 | pmid = 33069007 | pmc = 8044266 | url = }}</ref> many biomolecular condensates contain [[protein domain|multi-domain proteins]] constituted by folded domains connected by intrinsically disordered regions.<ref>{{cite web |url=https://wiki.cd-code.org/functional-type |title=Scaffolds and Clients |last=Ghosh |first= Soumyadeep |date=April 28, 2023 |website=CD-CODE Encyclopedia |access-date=May 28, 2023}}</ref> Current residue-level models are only applicable to the study of condensates of intrinsically disordered proteins and nucleic acids.<ref name="RegyDignonZheng2020">{{cite journal | last1 = Regy | first1 = Roshan Mammen | last2 = Dignon | first2 = Gregory L | last3 = Zheng | first3 = Wenwei | last4 = Kim | first4 = Young C | last5 = Mittal | first5 = Jeetain | title = Sequence dependent phase separation of protein-polynucleotide mixtures elucidated using molecular simulations | journal = Nucleic Acids Research | date = 2 December 2020 | volume = 48 | issue = 22 | pages = 12593–12603 | issn = 0305-1048 | eissn = 1362-4962 | doi = 10.1093/nar/gkaa1099 | pmid = 33264400 | pmc = 7736803 | url = }}</ref><ref name="JosephReinhardtAguirre2021"/><ref name="LeboldBest2022">{{cite journal | last1 = Lebold | first1 = Kathryn M. | last2 = Best | first2 = Robert B. | title = Tuning Formation of Protein–DNA Coacervates by Sequence and Environment | journal = The Journal of Physical Chemistry B | date = 23 March 2022 | volume = 126 | issue = 12 | pages = 2407–2419 | issn = 1520-6106 | eissn = 1520-5207 | doi = 10.1021/acs.jpcb.2c00424 | pmid = 35317553 | url = }}</ref><ref name="LeicherOsunsadeChua2022">{{cite journal | last1 = Leicher | first1 = Rachel | last2 = Osunsade | first2 = Adewola | last3 = Chua | first3 = Gabriella N. L. | last4 = Faulkner | first4 = Sarah C. | last5 = Latham | first5 = Andrew P. | last6 = Watters | first6 = John W. | last7 = Nguyen | first7 = Tuan | last8 = Beckwitt | first8 = Emily C. | last9 = Christodoulou-Rubalcava | first9 = Sophia | last10 = Young | first10 = Paul G. | last11 = Zhang | first11 = Bin | last12 = David | first12 = Yael | last13 = Liu | first13 = Shixin | title = Single-stranded nucleic acid binding and coacervation by linker histone H1 | journal = Nature Structural & Molecular Biology | date = 28 April 2022 | volume = 29 | issue = 5 | pages = 463–471 | issn = 1545-9993 | eissn = 1545-9985 | doi = 10.1038/s41594-022-00760-4 | pmid = 35484234 | pmc = 9117509 | url = }}</ref><ref name="FarrWoodsJoseph2021">{{cite journal | last1 = Farr | first1 = Stephen E. | last2 = Woods | first2 = Esmae J. | last3 = Joseph | first3 = Jerelle A. | last4 = Garaizar | first4 = Adiran | last5 = Collepardo-Guevara | first5 = Rosana | title = Nucleosome plasticity is a critical element of chromatin liquid–liquid phase separation and multivalent nucleosome interactions | journal = Nature Communications | date = 17 May 2021 | volume = 12 | issue = 1 | page = 2883 | eissn = 2041-1723 | doi = 10.1038/s41467-021-23090-3 | pmid = 34001913 | pmc = 8129070 | bibcode = 2021NatCo..12.2883F | url = }}</ref><ref name="Valdes-GarciaHeoLapidus2023"/> Including an accurate description of the folded domains in these models will considerably widen their applicability.<ref name="LathamZhang2022">{{cite journal | last1 = Latham | first1 = Andrew P. | last2 = Zhang | first2 = Bin | title = Unifying coarse-grained force fields for folded and disordered proteins | journal = Current Opinion in Structural Biology | date = February 2022 | volume = 72 | pages = 63–70 | issn = 0959-440X | doi = 10.1016/j.sbi.2021.08.006 | pmid = 34536913 | pmc = 9057422 | url = }}</ref><ref name="SaarQianGood2023"/>

=== Mechanical analysis of biomolecular condensates ===

To identify liquid-liquid phase separation and formation of condensate liquid droplets, one needs to demonstrate the liquid behaviors (viscoelasticity) of the condensates. Furthermore, mechanical processes are key to condensate related diseases, as pathological changes to condensates can lead to their solidification. Rheological methods are commonly used to demonstrate the liquid behavior of biomolecular condensates. These include active microrheological characterization by means of optical tweezers<ref>Ghosh, A., D. Kota, and H.-X. Zhou, Shear relaxation governs fusion dynamics of biomolecular condensates. Nature Communications, 2021. 12(1): p. 5995.</ref><ref>Jawerth, L., et al., Protein condensates as aging Maxwell fluids. Science, 2020. 370(6522): p. 1317-1323.</ref> and scanning probe microscopy.<ref>Aida Naghilou, Oskar Armbruster, Alireza Mashaghi, Scanning probe microscopy elucidates gelation and rejuvenation of biomolecular condensates. (2024) [https://www.biorxiv.org/content/10.1101/2024.08.28.610139v1 Link]</ref>

== See also ==
* [[List of liquid–liquid phase separation databases]]

== References ==
{{reflist}}

== Further reading ==
{{refbegin}}
* [[Philip Ball|Ball, Philip]], "A New Understanding of the Cell: Gloppy specks called biomolecular condensates are rewriting the story of how life works", ''[[Scientific American]]'', vol. 332, no. 2 (February 2025), pp. 22–27. "Biomolecular condensates now seem to be a key part of how life gets its countless molecular components to coordinate and cooperate, to form committees that make the group decisions on which our very existence depends." (p. 24.)
* {{cite journal | vauthors = Banani SF, Lee HO, Hyman AA, Rosen MK | title = Biomolecular condensates: organizers of cellular biochemistry | journal = Nature Reviews. Molecular Cell Biology | volume = 18 | issue = 5 | pages = 285–298 | date = May 2017 | pmid = 28225081 | pmc = 7434221 | doi = 10.1038/nrm.2017.7 | s2cid = 37694361 }}
* {{cite journal | vauthors = Ditlev JA, Case LB, Rosen MK | title = Who's In and Who's Out-Compositional Control of Biomolecular Condensates | journal = Journal of Molecular Biology | volume = 430 | issue = 23 | pages = 4666–4684 | date = November 2018 | pmid = 30099028 | pmc = 6204295 | doi = 10.1016/j.jmb.2018.08.003 }}
* {{cite journal | vauthors = Dolgin E | title = What lava lamps and vinaigrette can teach us about cell biology | journal = Nature | volume = 555 | issue = 7696 | pages = 300–302 | date = March 2018 | pmid = 29542707 | doi = 10.1038/d41586-018-03070-2 | doi-access = free | bibcode = 2018Natur.555..300D }}
* {{cite journal | vauthors = Hyman AA, Weber CA, Jülicher F | title = Liquid–liquid phase separation in biology | journal = Annual Review of Cell and Developmental Biology | volume = 30 | pages = 39–58 | year = 2014 | pmid = 25288112 | doi = 10.1146/annurev-cellbio-100913-013325 | doi-access = free }}
{{refend}}

[[Category:Organelles]]