Transmembrane coupling of liquid-like protein condensates

Abstract

Liquid-liquid phase separation of proteins occurs on both surfaces of cellular membranes during diverse physiological processes. In vitro reconstitution could provide insight into the mechanisms underlying these events. However, most existing reconstitution techniques provide access to only one membrane surface, making it difficult to probe transmembrane phenomena. To study protein phase separation simultaneously on both membrane surfaces, we developed an array of freestanding planar lipid membranes. Interestingly, we observed that liquid-like protein condensates on one side of the membrane colocalized with those on the other side, resulting in transmembrane coupling. Our results, based on lipid probe partitioning and mobility of lipids, suggest that protein condensates locally reorganize membrane lipids, a process which could be explained by multiple effects. These findings suggest a mechanism by which signals originating on one side of a biological membrane, triggered by protein phase separation, can be transferred to the opposite side.

The Two Levels of Podocyte Dysfunctions Induced by Apolipoprotein L1 Risk Variants

“…The activity of several cation channels, like Ca 2+ TRPC6 channels and Ca 2+ -dependent K + BK channels, which are both crucially involved in podocyte function [49][50][51][52][53][54][55][56][57][58], is regulated in lipid microdomains containing cholesterol at the outer membrane leaflet and PI(4,5)P2 at the inner leaflet [45][46][47][48][80][81][82][83][84][85] (Figure 4). Cholesterol-and sphingomyelin-rich regions in the outer leaflet align with clusters of PI(4,5)P2 in the inner leaflet by a mechanism termed trans-bilayer coupling [46,86]. Cholesterol controls the activity of the TRPC6 Ca 2+ channels, which mainly occurs at lipid rafts and is very sensitive to mechanical tension on these microdomains [87][88][89].…”

Sequence Sensitivity in Membrane Remodeling by Polyampholyte Condensates

“…Recent studies have suggested that LLPS at the lipid membrane is biologically important. − It was also observed that LLPS at the membrane surface can induce significant curvatures, local demixing, lipid ordering, vesicle biogenesis, and tubulation. − Therefore, LLPS near the membrane surface can serve as a novel mechanism for membrane remodeling in cells, in addition to the much discussed mechanisms such as hydrophobic insertion, scaffolding, protein crowding, and coating. − Despite the importance and interest in general, only a few theoretical investigations have been directed toward understanding the mechanism of LLPS-induced large-scale structural transformations of a lipid bilayer or vesicle, from a molecular perspective.…”