Complex Coacervate Formation on a Heterogeneous Membrane

Abstract

Mixtures of oppositely charged polymers in salt solutions can undergo liquid-liquid phase separation through a process called complex coacervation. Polyelectrolyte coacervates are liquid droplets enriched in both polymers and stabilized via electrostatic interactions that occur in three dimensions. Multicomponent lipid membranes can also undergo a liquid-liquid phase separation within the two-dimensional plane of the membrane. Phase separated membrane domains are enriched in particular lipid species and are stabilized via interactions between lipids that are highly temperature dependent. Here we investigate the coupling of these two distinct phase transitions by tethering polyelectrolytes directly to a lipid bilayer. We demonstrate that constraining one polymer to a uniform supported membrane supports polymer coacervation at much lower polymer concentrations than are required to form droplets in three-dimensions, consistent with previous reports. We are also investigating coacervate formation on multicomponent membranes capable of forming liquid-ordered and liquid-disordered phases, and can selectively conjugate polyelectrolytes to lipids that partition strongly into one phase. Our overall goal of this work is to investigate regimes where polymer interactions impact the organization of membrane lipids, or where heterogeneity of membrane lipids contributes to the stabilization of coacervates. Analogous coupling of phase transitions is hypothesized to occur in a variety of biological contexts, including at sites of immunoreceptor activation and neuronal synapses.