Experimental investigations of coupled polymer and membrane phase transitions.

Abstract

Polymers can separate into polymer dense and polymer dilute liquid phases in solution while multicomponent lipid membranes can separate into distinct phases within the two-dimensional plane of the membrane. Recent theoretical and simulation work predicts the presence of a polymer rich surface phase when these two-phase transitions are coupled by including polymer conjugated lipids in membranes, and that the location of this phase boundary is tuned by both polymer and lipid interactions1. Here, we experimentally observe the predicted domains of polymer rich surface phase when a small subset of polymers are conjugated to membranes. These surface phases appear at concentrations where polymers do not condense in the bulk, and the concentration needed to form surface phase depends on membrane composition. Experiments have been conducted both with a simple polyelectrolyte and with FUS proteins in separate measurements, demonstrating the robustness of this effect. 1. Rouches, M., Veatch, S. & Machta, B. Surface Densities Prewet a Near-Critical Membrane. bioRxiv2021.02.17.431700 (2021).