Protein Adsorption on Lipid Monolayers at their Coexistence Region

TL;DR

This paper presents a theoretical study of how proteins distribute themselves on lipid monolayers at the coexistence region, revealing conditions for localization, delocalization, and phase-dependent behavior.

Contribution

It introduces a mean-field model to predict protein distribution and phase behavior on lipid monolayers, aligning with recent experimental observations.

Findings

Proteins localize at phase boundaries when indifferent to amphiphile density.

A delocalization transition occurs with temperature or protein concentration changes.

Results are applicable to lipid multicomponent membranes with phase coexistence.

Abstract

We investigate theoretically the behavior of proteins as well as other large macromolecules which are incorporated into amphiphilic monolayers at the air-water interface. We assume the monolayer to be in the coexistence region of the ``main'' transition, where domains of the liquid condensed phase coexist with the liquid expanded background. Using a simple mean-field free energy accounting for the interactions between proteins and amphiphilic molecules, we obtain the spatial protein distribution with the following characteristics. When the proteins preferentially interact with either the liquid condensed or liquid expanded domains, they will be dissolved in the respective phase. When the proteins are energetically rather indifferent to the density of the amphiphiles, they will be localized at the line boundary between the (two-dimensional) liquid expanded and condensed phases. In between these two limiting cases, a delocalization transition of the proteins takes place. This transition is accessible by changing the temperature or the amount of incorporated protein. These findings are in agreement with recent fluorescence microscopy experiments. Our results also apply to lipid multicomponent membranes showing coexistence of distinct fluid phases.