Protein Export Across the E. coli Outer Membrane by the Autotrantransporter EspP

Abstract

Autotransporters are outer membrane proteins produced by Gram-negative bacteria that are involved in virulence and consist of two domains, an N-terminal “passenger domain” and a C-terminal “β-domain”. Passenger domains are secreted to the cell surface while β-domains are predicted to form β-barrel structures in the outer membrane. In some autotransporters, the secreted passenger domain is released from the β-domain by proteolytic cleavage. Using X-ray crystallography, we solved the 2.7 A structure of the post-cleavage state of the β-domain of EspP, an autotransporter produced by E. coli O157:H7. The structure consists of a 12-stranded β-barrel with the passenger / β-domain cleavage junction located inside the barrel pore, approximately mid-way between the extracellular and periplasmic surfaces of the outer membrane. The structure reveals an unprecedented intra-barrel cleavage mechanism and suggests that two conformational changes occur in the β-domain after cleavage, one conferring increased stability on the β-domain and another restricting access to the barrel pore. The location of the cleavage site within the beta barrel has implications for secretion of the passenger domain across the outer membrane.View Large Image | View Hi-Res Image | Download PowerPoint Slide