Characterization of the Moraxella catarrhalis Opa-like protein, OlpA, reveals a phylogenetically conserved family of outer membrane proteins

Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Canada M5S1A8; Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390

^* To whom correspondence should be addressed. Email: scott.gray.owen{at}utoronto.ca.

	Abstract

Moraxella catarrhalis is a human restricted pathogen that can cause respiratory tract infections. In this study, we identify a previously uncharacterized 24 kDa outer membrane protein with a high degree of similarity to Neisseria sp. Opa protein adhesins, with a predicted -barrel structure consisting of 8 anti-parallel -sheets with 4 surface-exposed loops. In striking contrast to the antigenically variable Opa proteins, the M. catarrhalis Opa-like protein (OlpA) is highly conserved and constitutively expressed, with 25 of 27 strains corresponding to a single variant. Protease treatment of intact bacteria and isolation of outer membrane vesicles confirm that the protein is surface exposed, yet does not bind host cellular receptors recognized by neisserial Opa proteins. Genome-based analyses indicate OlpA and Opa derive from a conserved family of proteins shared by a broad array of Gram negative bacteria.