autotranspordis

Autotransporters, also referred to as Type V secretion system proteins, are a class of bacterial outer membrane proteins that mediate the export of virulence factors and adhesins across the cell envelope. First identified in Escherichia coli, they typically consist of a single polypeptide chain that contains an N‑terminal passenger domain, a C‑terminal β‑barrel translocator domain, and a short periplasmic linker. The β‑barrel forms a pore in the outer membrane, through which the passenger domain is translocated to the cell surface or released into the extracellular environment.

The secretion mechanism is thought to be autonomous, relying on the folding and insertion of the β‑barrel into the membrane, followed by the unfolding of the passenger domain into the pore and refolding outside. Some autotransporters require the assistance of the Sec pathway for periplasmic translocation of the nascent chain.

Autotransporters are divided into several subfamilies based on structural and functional diversity: classical autotransporters, trimeric autotransporters, and those with hybrid domains such as autotransporter adhesins. It is estimated that over 300 distinct autotransporter proteins exist among Gram‑negative pathogens, including those that mediate adhesion to host cells, proteolysis, or immune evasion.

Because of their surface exposure, autotransporters are attractive targets for vaccine design and for the development of novel antimicrobial strategies. Their modular architecture also provides a model system for studying protein folding and membrane insertion.