The outer membrane efflux protein is a protein family member that forms trimeric (three-piece) channels allowing the export of a variety of substrates in gram-negative bacteria. Each efflux protein is composed of two repeats. The trimeric channel is composed of a 12-stranded beta-barrel that spans the outer membrane, and a long tail helical barrel that spans the periplasm.
Examples include the Escherichia coli TolC outer membrane protein, which is required for proper expression of outer membrane protein genes; the Rhizobium nodulation protein; and the Pseudomonas FusA protein, which is involved in resistance to fusaric acid.