With TolR probably plays a role in maintaining the position of the peptidoglycan cell wall in the periplasm. Acts as a porin with low permeability that allows slow penetration of small solutes; an internal gate slows down solute passage. Required for conjugation with F-type plasmids; probably serves as the mating receptor on recipient cells. (Microbial infection) Serves as a secondary receptor during phage Sf6 infection; infection requires both lipopolysaccharide (LPS) and the OmpA beta-barrel. Monomer and homodimer. (Microbial infection) Upon infection with phage Sf6 associates with the mature bacteriophage capsid (PubMed:21071053, PubMed:22386055). Was originally suggested to be within the bacteriophage capsid (PubMed:21071053). This has been disproven (PubMed:22386055). (Microbial infection) Upon infection with phage Sf6 is found in extracellular vesicles that associate with the tails of mature phage particles. The extracellular loops are most variable in sequence, and in some bacteria confer sensitivity to phage and/or colicins. No effect on propagation of phage Sf6 (PubMed:22386055). Upon infection with phage Sf6, single deletion mutant has a wild-type level of small plaques but a better than wild-type survival level; double ompA-ompC deletions have about 10-fold fewer plaques and survive infection considerably better than wild-type, are infected more slowly and have fewer extracellular vesicles associated with mature bacteriophage (PubMed:24673644). Belongs to the outer membrane OOP (TC 1.B.6) superfamily. OmpA family.