Part of the translocation and assembly module (TAM) autotransporter assembly complex, which functions in translocation of autotransporters across the outer membrane. Has anion selective channel-forming ability, but the physiological relevance of this activity is unclear. Interacts with TamB. Contains 3 N-terminal periplasmic polypeptide transport-associated (POTRA) domains and a C-terminal 16-stranded beta-barrel transmembrane region. The beta-barrel is closed on the extracellular face by loop 6 (residues 456-495), while the C-terminal beta-strand forms an inward kink which may act as a gate for substrate access from the periplasm. This kink weakens the beta-strand pair between the first and last strands which may contribute to gating and substrate translocation. Significantly reduced survival in human serum, probably due to complement-mediated killing. Belongs to the TamA family.