Lipid Raft Formation Driven by Push and Pull Forces

The lipid raft hypothesis is one of the most significant concepts that has emerged over the past two decades in cell membrane research. In essence, lipid rafts are thought to consist of tightly packed aggregates of cholesterol and sphingolipids that “float in a sea” of fluid phospholipid. Despite its popularity, many basic questions surrounding the lipid raft hypothesis remain to be answered. In particular, their size, their lifetimes and their biological functions have not yet been firmly established. At a more fundamental level, the forces that drive the formation of lipid rafts are not well understood. In this review, recent “nearest-neighbor recognition” (NNR) experiments are discussed that bear on these forces. In particular, these experiments have revealed a major and, heretofore, unrecognized role that polyunsaturated phospholipids are likely to play in the formation of lipid rafts.