(382e) Pre-Transition Effects and Self-Assembly of Proteins in Multi-Component Lipid Membranes

We model multi-component lipid membrane systems via statistical mechanical models, and in particular provide a framework in which the lipid raft hypothesis, where ordered domains of proteins and lipids dynamically assemble in an otherwise disordered membrane, can be understood. Lipid rafts are implicated in cellular phenomena such as signaling and cellular trafficking but difficult to probe experimentally due to their time and length scales, thus necessitating appropriate large scale theoretical and computational techniques to characterize their behavior. We expand on previous work that demonstrates proteins with hydrophobic thickness mismatch can exhibit pre-transition effects stabilizing an order-disorder interface, termed the orderphobic effect. This effect is mediated by a first-order phase transition between solid-ordered and liquid-disordered phases in a single component membrane system, and provides a mechanism for the assembly and mobility of proteins and phases in the membrane analogous to the hydrophobic effect. In this work, we extend the orderphobic and corresponding orderphilic effect to the liquid-disordered and liquid-ordered first-order phase transition found in cell membranes. We develop a model for multi-component membrane systems with proteins that allows for large scale mean field and simulation studies to probe phase and shape behavior on relevant biological time and length scales. The effects of single proteins on membrane phase and shape behavior are analyzed with respect to key membrane parameters and adjusting the strength of the orderphobic/orderphilic effect. The implications of this behavior with respect to protein assembly are discussed. We discuss the length and time scales of the emerging lipid rafts via composite phase and shape diagrams, comparisons to continuum results, and the effects of osmotic pressure.