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Many intrinsically disordered peptides have been shown to undergo liquid–liquid phase separation and form complex coacervates, which play various regulatory roles in the cell. Recent experimental studies found that such phase separation processes may also occur at the lipid membrane surface and help organize biomolecules during signaling events; in some cases, phase separation of proteins at the membrane surface was also observed to lead to significant remodeling of the membrane morphology. The molecular mechanisms that govern the interactions between complex coacervates and lipid membranes and the impacts of such interactions on their structure and morphology, however, remain unclear. Here we study the coacervation of poly-glutamate (E 30 ) and poly-lysine (K 30 ) in the presence of lipid bilayers of different compositions. We carry out explicit-solvent coarse-grained molecular dynamics simulations by using the MARTINI (v3.0) force-field. We find that more than 20% anionic lipids are required for the coacervate to form stable contact with the bilayer. Upon wetting, the coacervate induces negative curvature to the bilayer and facilitates local lipid demixing, without any peptide insertion. The magnitude of negative curvature, extent of lipid demixing, and asphericity of the coacervate increase with the concentration of anionic lipids. Overall, we observe a decrease in the number of contacts among the polyelectrolytes as the droplet spreads over the bilayer. Therefore, unlike previous suggestions, interactions among polyelectrolytes do not constitute a driving force for the membrane bending upon wetting by the coacervate. Rather, analysis of interaction energy components suggests that bending of the membrane is favored by enhanced interactions between polyelectrolytes with lipids as well as with counterions. Kinetic studies reveal that, at the studied polyelectrolyte concentrations, the coacervate formation precedes bilayer wetting.
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This content will become publicly available on December 1, 2027
Insights into de-mixing and morphology modulation in coacervate-membrane interactions from integrating experiments and simulations
Abstract Intrinsically disordered proteins can undergo liquid-liquid phase separation to form condensates or coacervates, which play numerous regulatory roles in the cell. Recently, it was recognized that membrane-adsorbed condensates are crucial for biomolecular localization, and in some cases, induce significant changes in membrane morphology. A detailed understanding of the underlying mechanisms remains incomplete. Here, we combine experiments and simulations to unravel structural and dynamic features of the coacervate/membrane interface across scales. We study poly-Lysine/poly-Aspartate (K10/D10) coacervates with different unilamellar liposomes. By combining confocal microscopy, hyperspectral imaging, fluorescence recovery after photobleaching, and two complementary coarse-grained approaches, we show that the membrane affinity of the K10/D10coacervate can be tuned by the anionic lipid content and quantified through the intrinsic contact angle, both in vitro and in silico. We find that the membrane in contact with the condensate displays a nearly two-fold reduced fluidity compared to the bare membrane. This is attributed to the crowding of lipids at the contact region, resulting in decreased area per lipid. Moreover, we observed local lipid de-mixing upon coacervate adsorption. This study provides an effective framework for integrating experiment and computation to characterize the properties of coacervate-membrane interfaces that are critical to the functional impacts of these interactions.
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- Award ID(s):
- 2154804
- PAR ID:
- 10701218
- Publisher / Repository:
- Nature Springer
- Date Published:
- Journal Name:
- Communications Chemistry
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2399-3669
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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