STRUCTURE OF THE OUTER-MEMBRANE PROTEIN-A TRANSMEMBRANE DOMAIN

The outer membrane protein A of Escherichia coli (OmpA) is an intensel y studied example in the field of membrane protein folding. We have de termined the structure of the OmpA transmembrane domain consisting of residues 1-171, by X-ray diffraction analysis, to a resolution of 2.5 Angstrom. It consists of a regular, extended eight-stranded beta-barre l and appears to be constructed like an inverse micelle with large wat er-filled cavities, but does not form a pore. Surprisingly, the caviti es seem to be highly conserved during evolution. The structure corrobo rates the concept that all outer membrane proteins consist of beta-bar rels. The structure constitutes a beta-barrel membrane anchor that app ears to be the outer membrane equivalent of the single-chain alpha-hel ix anchor of the inner membrane.