Translocation of autotransporters across the bacterial outer membrane: role of the Bam (Omp85)complex

Despite their complex cell envelope, Gram-negative bacteria secrete a wide variety of proteins into the extracellular milieu. Several pathways have evolved to enable protein transfer across the inner membrane, the periplasm and the outer membrane. The Autotransporter (AT) pathway, also known as type Va secretion, appears the most widely distributed secretion system and is typically used by virulence factors with diverse roles in pathogenesis. The original, presently controversial, concept of autotransport is simple proposing that the AT carries all information for translocation across the cell envelope within the AT itself. The concept implies that translocation of the functional N-terminal part of the AT (the passenger domain) across the bacterial outer membrane occurs through a pore that is formed by the C-terminal part of the AT (the beta-domain). However, recent structural analysis of different beta-domains reveals pores that are too narrow to accommodate the partly folded structures known to be translocated via this pathway. In this project we will analyze the role of the recently identified beta-barrel assembly machine (Bam; also known as Omp85-complex) in autotransport as exciting novel data implicate this complex in the translocation of ?our? model AT Haemoglobin protease (Hbp) thus challenging the AT concept. By investigating the role of Bam in autotransport we also expect to obtain information on the role of Bam in the biogenesis of outer membrane proteins, another topical issue in microbiology.