The OEP family (Outer membrane efflux protein) form trimeric channels that allow export of a variety of substrates in Gram negative bacteria. Each member of this family is composed of two repeats. The trimeric channel is composed of a 12 stranded all beta sheet barrel that spans the outer membrane, and a long all helical barrel that spans the periplasm.

1: Alignment and structure prediction of divergent protein families: periplasmic and outer membrane proteins of bacterial efflux pumps. Johnson JM, Church GM; J Mol Biol 1999;287:695-715. PMID:10092468