Autotransporters are produced by a large variety of Gram-negative bacteria. These cell-surface-exposed and secreted protein have been intensively studied because many of them have virulence-related functions. among the various secretion pathways recognism to date in Gram-negative bacteria,the AT mechanism seems to represent a relatively simple pathway. The secretion mechanism does not require dedicated secretion machinery but parasitizes on general machinery required for bacterial physiology, i.e the Sec system, which constitutes the general export pathway for periplasmic and outer-membrane protein (OMPs),and the Ban complex which assembles integral OMPs into the outer membrane ATs are synthesized as large precursor with an N-terminal signal sequence, a translocator domain (TD),and a passenger ,