This family consists of several adhesins found in Neisseria species. OpcA is an integral outer membrane protein from Neisseria meningitidis, the causative agent of meningococcal meningitis and septicemia. It mediates the adhesion of Neisseria meningitidis to epithelial and endothelial cells by binding to vitronectin and proteoglycan cell-surface receptors. The crystal structure of OpcA has been determined to 2.0 A resolution, showing a 10-stranded ß-barrel structure with extensive loop regions that protrude above the predicted surface of the membrane. Loops 2, 3, 4 and 5 associate to form one side of a crevice in the external surface of the structure, the other side being formed by loop 1. OpcA is one of the Major Outer Membrane Proteins and has been shown to play an important role in meningococcal adhesion and invasion of both epithelial and endothelial cells.

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