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J Bacteriol. 2007 Jan;189(1):76-82. Epub 2006 Oct 13.

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

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  • 1Department of Medical Genetics and Microbiology, Room 4381, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario M5S 1A8, Canada.


Moraxella catarrhalis is a human-restricted pathogen that can cause respiratory tract infections. In this study, we identified a previously uncharacterized 24-kDa outer membrane protein with a high degree of similarity to Neisseria Opa protein adhesins, with a predicted beta-barrel structure consisting of eight antiparallel beta-sheets with four 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 that OlpA and Opa derive from a conserved family of proteins shared by a broad array of gram-negative bacteria.

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