ompA

ompA is a gene name used in several Gram-negative bacteria to denote an outer membrane protein A, a component of the outer membrane that influences permeability, structural integrity, and interactions with the environment. In many Enterobacteriaceae, including Escherichia coli, ompA encodes a conserved outer membrane protein A that functions as a porin-like, beta-barrel protein and also has a periplasmic domain that anchors to the peptidoglycan layer. The protein is typically about 35–38 kDa in mass after processing and is produced as part of the bacterial envelope, contributing to membrane stability and, in some contexts, to interactions with host cells. OmpA also affects susceptibility to certain antibiotics, biofilm formation, and attachment to surfaces or tissues. Its expression is modulated by environmental conditions and stress responses.

In Chlamydia species, the same gene symbol ompA refers to the major outer membrane protein (MOMP), a distinct functional class of porin that is a dominant antigen and determinant of serovar identity. MOMP is a primary surface-exposed protein, forms a trimeric porin, and exhibits substantial sequence variability that underpins serotyping. It plays roles in host cell interaction, immune recognition, and pathogenesis, and is a key target for diagnostics and vaccine research in chlamydial infections.

Across species, ompA homologs generally encode outer membrane constituents that influence permeability, structural integrity, and host interactions, but the exact structure and function can vary. The term thus encompasses multiple, related proteins with roles in membrane biology and virulence.