Bacterial autotransporters

Autotransporters are multi-domain proteins found in a variety of Gram-negative bacteria. They consist of a short signal sequence, a large passenger domain and a smaller relatively conserved 440-residue C-terminal membrane-bound beta-domain. The passenger domain is displayed on the cell surface. Although its sequence is not well conserved between species, computer programs predict a common structure in the form of parallel beta-helices   . The beta-domain, which translocates the passenger domain through a pore to present it on the cell surface, is believed to be a 14-strand beta-barrel. However, no atomic-scale structures of autotransporter domains are known. Autotransporters insert into the outer membrane by a mechanism that apparently does not involve chaperones, but the detailed mechanism of insertion of the beta-domain and extrusion of the passenger domain is unknown.     Among these autotransporters, AIDA (adhesin involved in diffuse adherence) and antigen 43 (Ag43) are particularly well characterized. AIDA was originally isolated in an enterotoxigenic strain of and was the first bacterial protein to be shown to be post-translationally glycosylated, the glycosylation agent being the heptosyltransferase AAH. After transport to the outer membrane, proteolytic processing cleaves the passenger domains from the membrane domain, although the two domains remain associated; the boundary between the passenger domain and membrane-domain has been identified. The membrane domain has been purified and refolded (J.E. Mogensen, M.A. Schmidt, D. Tapadar and D.E. Otzen, mauscript in preparation). Its glycoprotein receptor in mammalian cells has been identified. Furthermore the membrane-domain has been shown to be a very useful carrier for display of peptides and functional proteins.   E. coli     in vitro     Samarbejdspartner: Per Klemm (DTU)