Preprotein Binding by the SecA ATPase

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The research proposal addresses bacterial protein secretion, the process by which bacteria transport protein molecules from their site of synthesis inside the cell, to the exterior environment. All bacteria have a "General Secretory System" (GSS), or "Preprotein Translocase", that is able to recognize proteins that are destined for secretion (proteins with a secretory signal sequence, otherwise known as "preproteins"). Once they are recognized as secretory proteins, preproteins are prevented from folding, and then targeted to sites on the cell membrane where they can be passed through a pore to the outside environment, a process termed "translocation". The targeting and translocation processes are mediated by the SecA ATPase, which uses the energy of ATP hydrolysis to catalyze protein secretion. This GSS is absolutely required for bacterial growth, and is not present in mammalian cells. On this basis, the GSS, and in particular the SecA ATPase, are good potential targets for therapeutic antibiotics. In addition, certain bacteria, such as Mycobacterium tuberculosis, contain two SecA molecules, SecA1 and SecA2. SecA2 fulfills specialized functions including the secretion of virulence factors that allow the bacteria to survive in host cells. Therefore, increasing our understanding of how the GSS works could open new avenues for antimicrobial therapies. A deeper knowledge of GSS function will also enable the development of novel systems for protein expression and secretion in bacteria for biotechnological applications. The proposed research is focussed on understanding how SecA binds to its preprotein substrates. This binding interaction is important for the initial recognition of the preprotein, which takes place at the ribosome as the preprotein is synthesized, and ensures that the preprotein is correctly targeted to the secretion pathway. SecA-preprotein interactions are also important for translocation, where the preprotein is guided through a membrane pore by SecA.