Transbilayer movement of phospholipids in biogenic membranes.

Biogenic membranes contain the enzymes that synthesize the cell's membrane lipids, of which the phospholipids are the most widespread throughout nature. Being synthesized at and inserted into the cytoplasmic leaflet of biogenic membranes, the phospholipids must migrate to the opposite leaflet to ensure balanced growth of the membrane. In this review, the current knowledge of transbilayer movement of phospholipids in biogenic membranes is summarized and the available data are compared to what is known about lipid translocation in other membranes. On the basis of this, a mechanism is proposed, in which phospholipid translocation in biogenic membranes is mediated via membrane-spanning segments of a subset of proteins, characterized by a small number of transmembrane helices. We speculate that proteins of this subset facilitate lipid translocation via the protein-lipid interface, because they display more dynamic behavior and engage in less stable protein-lipid interactions than larger membrane proteins.