The Bacterial Secretosome

所有的细胞都被膜包围，膜由一层叫做磷脂的脂肪分子组成。细胞膜扮演着分子“皮肤”的角色，将细胞内部隔离开来，分离不同的生化反应。需要以有控制的方式打破这一障碍，以允许营养物质、废物的运输以及与外部世界的沟通；这是通过广泛的膜插入蛋白质实现的。我们对膜蛋白所具有的运输、呼吸、光合作用等多种生物学功能有了很深的了解。然而，我们对膜是如何形成的，或者关于蛋白质在生物发生过程中必要的跨膜或进入膜的运输知之甚少。我们的建议旨在更多地了解细胞的蛋白质分泌是如何发生的。分泌(简称SEC)机制对生命至关重要--对每个有机体中的每一个细胞都是如此。该项目涉及这一过程，在非常简单的细菌细胞中。细菌分泌的蛋白质可用于广泛的细胞膜和细胞外活动，包括：细胞黏附、致病、抗生素的降解，还包括保护细胞壁的生物发生。革兰氏阴性杆菌是一类主要的细菌，它的细胞壁由外膜包围的周质和肽聚糖(PG)层组成。细胞壁的生物发生依赖于通过SEC机制从细胞内部分泌的蛋白质。周质的蛋白质可以很容易地折叠并留在那里。蛋白质也通过另一种名为BAM复合体的运输机器运输穿过或进入外膜，但目前尚不清楚它们是如何往返于那里，以确保这一过程快速有效。我们已经确定了内质膜的SEC机械与BAM复合体之间的相互作用，形成了一种跨越整个细胞壁的结构。我们称之为细菌‘分泌体’的这种巨大的组装，可以形成一个连续的管道，非常有效地将蛋白质从胞浆输送到外膜。它的存在将对我们对外膜生物发生的理解产生深远的影响。该项目将利用生物化学方面的互补专业知识，以及光学和高分辨率电子冷冻显微镜成像方面的新突破性技术。这些科学方法将阐明分泌体的结构以及它是如何工作的。该项目的结果将是重要的，因为细菌细胞壁很容易受到攻击。细胞壁的削弱，或者其生物发生或再生能力的妥协可能是致命的。因此，我们对细菌分泌体及其在维持细胞壁中的作用的了解的新信息，可能会提出颠覆细菌分泌体的方法，以开发新的抗生素。这将在我们对抗抗菌素耐药性(AMR)的斗争中产生急需的弹药。

All cells are surrounded by membranes, made up from a double layer of fatty molecules called phospholipids. Cell membranes act as a molecular "skin", keeping the cell's insides in, and separating different biochemical reactions. The barrier needs to be breached in a controlled manner to allow transport of nutrients, waste products and for communication with the outside world; this is achieved by a wide range of membrane-inserted proteins. We understand a great deal about the diverse biological functions that membrane proteins bestow, such as transport, respiration, photosynthesis. However, we know very little about how membranes are formed, or about the necessary transport of proteins across or into membranes during their biogenesis.Our proposal aims to understand more about how the cell's protein secretion occurs. The secretory ('Sec' for short) machinery is essential for life - for every cell in every organism. The project concerns this process, in very simple bacterial cells. Bacteria secrete proteins for a wide range of membrane and extracellular activities including for: cell adherence, pathogenicity, the degradation of antibiotics, including also the biogenesis of the protective cell wall. A major class of bacteria known as Gram-negatives, possess a cell wall composed of a periplasm with a peptidoglycan (PG) layer, surrounded by an outer-membrane. The biogenesis of the cell wall is dependent on protein secretion through from the cell interior through the Sec machinery. Proteins of the periplasm can readily fold and remain there. Proteins are also transported across or into the outer membrane by another transport machine called the BAM complex, but it is not clear how they are shuttled there, to ensure the process is rapid and efficient.We have identified an interaction between the Sec machinery of the inner plasma membrane and the BAM complex, forming a structure that spans the entirety of the cell wall. This giant assembly, which we have called the bacterial 'secretosome', could form a contiguous conduit for very efficient passage of proteins from the cytosol to the outer-membrane. Its existence will have far reaching implications for our understanding of outer-membrane biogenesis.The project will harness complementary expertise in biochemistry and new breakthrough technologies in imaging by light and high-resolution electron cryo-microscopy. These scientific methods will illuminate the architecture of the secretosome, and how it works. The results of the project will be important because the bacterial cell wall, is vulnerable to attack. The weakening of the cell wall, or a compromise in its biogenesis or regenerative capabilities could be lethal. Therefore, new information towards our understanding of the bacterial secretosome, and its action in the maintenance of the cell wall, could suggest ways in which it could be subverted towards the development of new antibiotics. This would generate much needed ammunition in our fight against antimicrobial resistance (AMR).