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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:Size scaling of phase-separated domains and mesosc
 ale clusters that precede liquid-liquid phase sepa
 ration (LLPS): theory and experiment - Samuel Safr
 an (Weizmann Institute of Science)
DTSTART;TZID=Europe/London:20231009T094000
DTEND;TZID=Europe/London:20231009T104000
UID:TALK204799AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/204799
DESCRIPTION:Gonen Golani\, Maria Oranges\, Manas Seal\, Alexey
  Bogdanov\, Daniella Goldfarb\, Samuel Safran\nDep
 artment of Chemical and Biological Physics\, Weizm
 ann Institute of Science\, Rehovot\, Israel\nWe re
 view the theoretical and experimental understandin
 g of how domain sizes are fixed in LLPS in the cas
 es of (i) equilibrium phase separation in a confin
 ed system (chromatin in the nucleus [1]) and (ii) 
 non-equilibrium phase separation (e.g.\, solute pr
 oduction and degradation\, see poster by Amit Kuma
 r). &nbsp\;We then discuss observations [2\,3] &nb
 sp\;of large (10&rsquo\;s-100 nm&rsquo\;s) protein
  assemblies in the one-phase regime that precedes 
 LLPS. We have formulated an analytical theory of t
 hese protein assemblies based on analogies with ot
 her mesoscale structures in amphiphilic (surfactan
 t or lipid) systems where core-shell assemblies ar
 e observed. What is unique about intrinsically dis
 ordered proteins is that the same protein can &nda
 sh\; via its different conformations [4] -- act as
  both the &ldquo\;inner phase&rdquo\; and &ldquo\;
 amphiphilic surface layer.&rdquo\;&nbsp\; This is 
 consistent with Ref. 2 that identified two types o
 f dynamics associated with the &ldquo\;clusters&rd
 quo\;. &nbsp\;Thus\, relatively large assemblies c
 an be stable for even a single protein in water wi
 th no amphiphile or &ldquo\;internal phase&rdquo\;
  required. We formulate a statistical mechanics mo
 del of such core-shell assemblies to predict the s
 ize distribution of the observed &ldquo\;clusters&
 rdquo\; in the one-phase region and compare it wit
 h the results of light scattering experiment [2\, 
 3]. The data for relatively large clusters is well
 -fit by a model with interfacial tension\, while t
 he fits for smaller clusters must also account for
  the bending energy and geometric corrections. In 
 addition\, electron spin-resonance experiments [3]
  estimate the core-shell volume ratios\, indicatin
 g that at the LLPS transition\, there is no sharp 
 change in the rotational time scales of the protei
 ns in the core and shell. This may suggest that\, 
 in these cases\, the LLPS may arise from attractio
 n-induced phase separation of the &ldquo\;clusters
 \,&rdquo\; similar to phase separations in some sp
 herical microemulsions [5].\n[1] Amiad-Pavlova et 
 al.\, Sci. Adv. (2021) 7\, eabf6251\; Bajpai et al
 .\, eLife (2021) 10\, e63976.\n[2] M. Kar et al.\,
  PNAS (2022) 119\, e2202222119.\n[3] M. Seal et al
 .\, J. Phys. Chem. B (2021) 125\, 12947.\n[4] Mugn
 ai et al.\, BioArchiv (2023).\n[5] J. S. Huang et 
 al.\, Phys. Rev. Lett. (1981) 47\, 1462 and (1984)
  53\, 592.\n&nbsp\;
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:
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