Probing the mechanism of protein export by the bacterial Tat transport system

所有的细菌都产生在细菌细胞外运作的蛋白质。一个很好的例子是细菌病原体产生的毒素。由于所有的蛋白质都是在细菌内部产生的，因此细胞外的蛋白质必须穿过通常不可渗透的细胞膜移出细胞。这一任务是由位于细胞膜上的蛋白质转运蛋白完成的。达特系统存在于许多不同的细菌中，包括那些引起人类疾病的细菌，如结核分枝杆菌（引起结核病）和沙门氏菌（引起食物中毒）。科学家们已经证明，对于许多不同的致病细菌，达特系统是它们致病的关键，他们对开发阻止达特系统工作的药物越来越感兴趣。大肠杆菌中的达特转运蛋白是一个由三种蛋白质组成的大蛋白复合体，分别命名为TatA、TatB和TatC。这些蛋白质被组织成两个不同的子复合物。存在由等量的TatB和TatC组成的子复合物。这种亚复合物在识别将要跨膜转运的蛋白质方面起着非常重要的作用。另一个亚复合体由许多TatA蛋白的拷贝组成。为了了解达特机制的工作原理，并最终设计出阻止它工作的新药，我们需要知道亚复合体中不同的蛋白质（或亚基）是如何排列的。该应用程序旨在了解TatBC子综合体的组织方式。在这个项目中，我们想回答的一些问题是（i）TatB和TatC蛋白之间的界面在哪里？(ii)在蛋白质通过达特途径转运的过程中，界面如何改变以允许TatB和TatC动态移动？最后，我们知道，在蛋白质通过达特系统的运输过程中，TatA和TatBC亚复合物一起运输蛋白质。我们相信，当这种情况发生时，TatA可能会以与TatB相同的方式与TatC结合，我们想通过进行类似的实验来测试这一点。

All bacteria produce proteins that operate on the outside of the bacterial cell. A good example of this is the toxins produced by bacterial pathogens. Since all proteins are made inside the bacterium, the extracellular proteins must be moved out of the cell across the normally impermeable cell membrane. This task is carried out by machines termed protein transporters that are located in the cell membrane. The Tat system is found in many different bacteria, including those which cause human diseases such as Mycobacterium tuberculosis (which causes tuberculosis) and Salmonella (which causes food poisoning). Scientists have shown for many different pathogenic bacteria that the Tat system is essential for them to cause disease, and they are becoming increasingly interested in developing drugs that prevent the Tat system from working.In the bacterium E. coli, the Tat transporter is a large protein complex made up of three types of proteins, named TatA, TatB and TatC. These proteins are organised into two different sub-complexes. There is a sub-complex made up of equal amounts of TatB and TatC. This sub-complex plays a very important role in recognising the proteins that are going to be transported across the membrane. The other sub-complex is made up of many copies of the TatA protein. This forms the channel in the membrane through which the proteins are transported.In order to understand how the Tat machinery works, and ultimately to design new drugs to stop it working, we need to know how the different proteins (or subunits) in the sub-complexes are arranged. This application is aimed at understanding how the TatBC sub-complex is organised. Some of the questions we want to answer in this project are (i) where are the interfaces between the TatB and TatC proteins located? (ii) How do the interfaces change to allow dynamic movement of TatB and TatC during the transport of proteins through the Tat pathway? Finally we know that during the transport of proteins through the Tat system the TatA and TatBC subcomplexes come together to transport proteins. We believe that when this happens TatA might bind to TatC in the same way that TatB does, and we would like to test this by carrying out similar experiments.