Does not bind carcinoembryonic antigen (CEA). 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. Monomer and homodimer. The extracellular loops are most variable in sequence, and in some bacteria confer sensitivity to phage and/or colicins. On a 2D-gel the determined pI of this protein is: 5.5, its MW is: 32 kDa. Belongs to the outer membrane OOP (TC 1.B.6) superfamily. OmpA family.