Exploiting the structure of the twin-arginine protein translocase core

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Some proteins in bacteria are located outside the membrane that surrounds the cell, for example the toxins produced by bacterial pathogens. Because all proteins are made inside the bacterium the external proteins have to be moved out of the cell across the normally impermeable cell membrane by machines termed protein transporters. One type of transporter moves unfolded proteins, threading them across the membrane like string through the eye of a needle. By contrast, a second type of transporter, which we term the Tat system, moves folded proteins across the membrane. This is much more challenging than threading and so it is thought that the Tat system operates by an unusual mechanism. The Tat system is required for many bacterial processes including energy generation, cell division, nutrient acquisition, pathogenesis, and the nitrogen-fixing symbiosis of soil bacteria with plants. The Tat protein transport system is not only found in bacteria but is also present in the chloroplasts of plants where it is essential to form and maintain the proteins required to carry out photosynthesis. The Tat system is a possible drug target because it is required for bacterial pathogenesis but is not found in humans or animals. It is also of biotechnological interest because it could be utilised to secrete useful protein products. We have recently determined the molecular structure of the core part of the Tat protein translocation apparatus. This project aims to exploit this structural data to help us understand how the Tat machinery works.