Understanding the role of the outer membrane translocator in autotransporter biogenesis

To survive bacteria must produce proteins which are located on their cell-surface and which are secreted into the external environment. In order to get the proteins from the cytoplasm of the cell to the surface the bacterium must transport them across lipid membranes, which in effect actually pose a barrier to secretion. Thus bacteria have evolved specialized machineries which allow them to move proteins across the lipid membranes. One such mechanism is the autotransporter system. This is the most widely used protein secretion system within the Gram-negative bacteria. The overall objective of this proposal is an in-depth analysis of certain aspects of autotransporter protein secretion. The study of these proteins and in fact the study of secretion systems in general, is aimed at several important objectives. First, since bacterial pathogens need to export proteins to effect virulence the study of secretion systems provides information about the pathogenic strategies of the particular genus and species. Second, the study of secretion systems provides new opportunities to attenuate bacteria in the pursuit of anti-infective strategies. A third benefit of understanding secretion systems is that these systems can potentially be exploited for the delivery of foreign antigens as part of novel vaccine delivery systems. The importance of understanding the autotransporters is illustrated by the fact that in some cases these are essential virulence factors and in other cases they form part of current human vaccines

Secretion of proteins outside of Gram-negative bacteria necessitates passage through the inner membrane, the periplasm and the outer membrane. This formidable series of obstacles can be overcome only by sophisticated biological machineries. The simplest and most widely utilised secretion systems fall under the rubric of Type V secretion, as designated by Henderson et al. This category comprises those proteins secreted by the classical autotransporter (AT) system (type Va).The beta-domain is an essential feature of the AT protein secretion system. It represents the C-terminal portion of the autotransporter molecule and forms a pore structure in the outer membrane which allows secretion of the functional domain to the extracellular milieu. Here we wish to investigate how the beta-domain functions. By understanding how the beta-domain functions we may be able to design strategies to abrogate secretion of the functional domain and thus attenuate bacterial virulence. Additionally, understanding how the beta-domain functions will inform our attempts to use the ATs as a protein production platform, by allowing us to understand the versatility and limitations of the AT protein production system.