What drives the clustering of membrane-bound Ras?

The dynamic assembly and lateral organization of Ras proteins on the plasma membrane has been the focus of much research in recent years. It has been shown that different isoforms of Ras proteins share a nearly identical catalytic domain, yet form distinct and non-overlapping nanoclusters. Though this difference in the clustering behavior of Ras proteins has been attributed largely to their different C terminal lipid modification, its precise physical basis was not determined. Recently, we used computer simulations to study the mechanism by which the triply lipid-modified membrane-anchor of H-ras, and its partially de-lipidated variants, form nanoclusters in a model lipid bilayer. We found that the specific nature of the lipid modification is less important for cluster formation, but plays a key role for the domain-specific distribution of the nanoclusters. Here we provide additional details on the interplay between bilayer structure perturbation and peptide-peptide association that provide the physical driving force for clustering. We present some thoughts about how enthalpic (i.e., interaction) and entropic effects might regulate nanocluster size and stability.