Kinetics of symmetry and asymmetry in a phase-separating bilayer membrane

Abstract: We simulate a phase-separating a bilayer in which the leaflets experience a direct coupling favouring local compositional symmetry ("registered" bilayer phases), and an indirect coupling due to hydrophobic mismatch that favours strong local asymmetry ("antiregistered" bilayer phases). For wide ranges of overall leaflet compositions, multiple competing states are possible. For estimated physical parameters, a quenched bilayer may first evolve toward a metastable state more asymmetric than if the leaflets were uncorrelated;\ subsequently, it must nucleate to reach its equilibrium, more symmetric, state. These phase-transition kinetics exhibit characteristic signatures through which fundamental and opposing inter-leaflet interactions may be probed. We emphasise how bilayer phase diagrams with a separate axis for each leaflet can account for overall and local symmetry/asymmetry, and capture a range of observations in the experiment and simulation literature.