Autotransporter Domain

In molecular biology an autotransporter domain is a structural domain found in some outer membrane proteins.

Translocation of polypeptide chains through the outer membrane of Gram-negative bacteria is termed secretion. Secretion occurs via a number of different pathways in this type of bacterium. One of these pathways, known as the type V(a) secretion pathway is exemplified by the prototypical IgA1 Protease of Neisseria gonorrhoeae. In fact the type V(a), or autotransporter secretion pathway, constitutes the largest number of secreted virulence factors of any one of the seven known types of secretion from Gram-negative bacteria.

The protein domain shown to be absolutely necessary to mediate secretion through the outer membrane is contained within the C-terminal portion of the translated protein itself, which undergoes post-translational modification prior to secretion of a passenger domain, hence proteins secreted in this way are called autotransporters. The C-terminal translocator domain corresponds to an outer membrane beta-barrel domain. The N-terminal passenger domain is translocated across the membrane, and may or may not be cleaved from, and may or may not remain associated with, the translocator domain. In those proteins where the cleavage is auto-catalytic, the peptidase domains belong to MEROPS peptidase families S6 and S8. Passenger domains structurally characterised to date have been shown to be dominated by a protein fold known as a beta helix, the folding of which is thought to be intrinsically linked to its method of outer membrane translocation.