Structural commonalities among integral membrane enzymes

Abstract

The X-ray crystal structures of five distinct enzymes (prostaglandin H(2) synthase, squalene cyclase, fatty acid amide hydrolase, microsomal cytochrome P450, and estrone sulfatase) challenge contemporary descriptions of integral membrane proteins. This structurally divergent group represents an important component of the integral membrane proteome that lies at the bilayer's aqueous interface. We summarize here what is collectively understood about the membrane insertion of these proteins, what roles they may play in lipid biology, and their relationship to soluble structural homologs.