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SUMMARY:Size scaling of phase-separated domains and mesoscale clusters tha
 t precede liquid-liquid phase separation (LLPS): theory and experiment - S
 amuel Safran (Weizmann Institute of Science)
DTSTART:20231009T084000Z
DTEND:20231009T094000Z
UID:TALK204799@talks.cam.ac.uk
DESCRIPTION:Gonen Golani\, Maria Oranges\, Manas Seal\, Alexey Bogdanov\, 
 Daniella Goldfarb\, Samuel Safran\nDepartment of Chemical and Biological P
 hysics\, Weizmann Institute of Science\, Rehovot\, Israel\nWe review the t
 heoretical and experimental understanding of how domain sizes are fixed in
  LLPS in the cases of (i) equilibrium phase separation in a confined syste
 m (chromatin in the nucleus [1]) and (ii) non-equilibrium phase separation
  (e.g.\, solute production and degradation\, see poster by Amit Kumar). &n
 bsp\;We then discuss observations [2\,3] &nbsp\;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 these protein assemblies base
 d on analogies with other mesoscale structures in amphiphilic (surfactant 
 or lipid) systems where core-shell assemblies are observed. What is unique
  about intrinsically disordered 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 i
 s consistent with Ref. 2 that identified two types of dynamics associated 
 with the &ldquo\;clusters&rdquo\;. &nbsp\;Thus\, relatively large assembli
 es can be stable for even a single protein in water with no amphiphile or 
 &ldquo\;internal phase&rdquo\; required. We formulate a statistical mechan
 ics model of such core-shell assemblies to predict the size distribution o
 f the observed &ldquo\;clusters&rdquo\; in the one-phase region and compar
 e it with the results of light scattering experiment [2\, 3]. The data for
  relatively large clusters is well-fit by a model with interfacial tension
 \, while the fits for smaller clusters must also account for the bending e
 nergy and geometric corrections. In addition\, electron spin-resonance exp
 eriments [3] estimate the core-shell volume ratios\, indicating that at th
 e LLPS transition\, there is no sharp change in the rotational time scales
  of the proteins in the core and shell. This may suggest that\, in these c
 ases\, the LLPS may arise from attraction-induced phase separation of the 
 &ldquo\;clusters\,&rdquo\; similar to phase separations in some spherical 
 microemulsions [5].\n[1] Amiad-Pavlova et al.\, Sci. Adv. (2021) 7\, eabf6
 251\; 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) 12
 5\, 12947.\n[4] Mugnai 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
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