Part of the translocation and assembly module (TAM) autotransporter assembly complex, which functions in translocation of autotransporters across the outer membrane. Substrate binding to TamA moves its POTRA domains about 30 Angstroms into the periplasm, which would deform either the outer membrane or TamB and may provide force to reset TAM (By similarity). Interacts with TamA. The periplasmic domain is elongated (up to 160 Angstroms long) and forms contacts to the N-terminal POTRA domains of TamA. Belongs to the TamB family.