Characterization of a novel protein translocation system found ubiquitously in the membranes of Gram-negative bacteria

Bacteria have evolved complex protein machinery to secrete proteins into the environment. In Gram-negative bacteria, secreted substrates require efficient targeting and translocation across the inner- and outer-membrane by protein secretion systems. The Omp85 protein superfamily is evolutionarily conserved and functions by translocating substrates into, or across, the outer membrane of Gram-negative bacteria. This thesis describes the discovery of a novel protein secretion machine that is required for the efficient delivery of a group of surface exposed proteins called autotransporters. We have named this protein secretion system the translocation and assembly module (TAM) which is composed of the Omp85 outer membrane component TamA and the inner membrane protein TamB which together interact to form a complex spanning the periplasmic space. Chapter three describes the genomic relationship between tamA and tamB and a bioinformatic analysis of the protein subdomains. The protein products within the operon were then localized and their membrane topology determined. Chapter 4 presents the protein-protein interactions within the TAM complex. Finally, determination of the function of the TAM complex and the requirements for particular subdomains is presented in Chapter 5. Together, these findings have uncovered a novel protein secretion system within the membranes of Gram-negative bacteria. Further, this work has elucidated the function of this protein complex as a mediator of efficient secretion of autotransporters. Due to the virulence associate functions of autotransporter substrates, therapeutic inhibition of the TAM complex may prove to be a viable pursuit to inhibit Gram-negative bacterial infections.