Shigella flexneri O antigen polysaccharides: biosynthesis, function in virulence, and interaction with IcsA/VirG

福氏志贺氏菌每年导致数百万人痢疾。细菌侵入大肠细胞并在其中复制。在细胞内，S.福氏杆菌能够利用宿主细胞的肌动蛋白为基础的运动机制，在细胞内变得能动，这可以被看作是从细胞一端延伸的F-肌动蛋白彗星尾。位于外膜中的细菌细胞表面组分对于细菌引起疾病的能力是重要的。这些组分中的两种（脂多糖（LPS）及其多糖链（O抗原）和IcsA-VirG蛋白））是启动肌动蛋白聚合所必需的，并且影响这些组分合成的突变降低了引起疾病的能力。在以往的研究中，我们发现O抗原与IcsA的合成和功能是相互关联的。该项目将研究O抗原是如何合成的，它们的链长是由Wzz蛋白决定的，Wzz结构与其功能的关系也将被表征。将研究O抗原在细胞内运动中所起的作用，以确定所涉及的机制。细胞和无细胞提取物、抗体和特异性降解O抗原的酶的感染将用于研究O抗原如何影响细菌与人类细胞蛋白之间的相互作用。将使用针对IcSA的单克隆抗体研究O抗原与IcSA功能之间的关系。将研究LPS对外膜蛋白酶IcsP的影响，以及LPS脂质A突变对O抗原和毒力的影响。这些研究将有助于更好地了解一种普遍存在的细菌细胞表面组分（O抗原）的生物合成，其作为细菌与宿主细胞相互作用中的毒力因子的功能。这可能导致新的治疗策略，以预防和控制志贺氏菌病和其他细菌感染。

Shigella flexneri bacteria cause dysentery in millions of humans each year. The bacterium invades and replicates within the cells of the large intestine. Inside cells, S. flexneri is able to use the host cell's actin-based motility machinery to become motile within the cells, and this can be seen as F-actin comet tails extending from one end of the cell. Bacterial cell surface components residing in the outer membrane are important for the bacterium's ability to cause disease. Two of these components (lipopolysaccharides (LPS) and their polysaccharide chains (O antigens), and IcsA-VirG protein)) are required for initiating actin polymerisation, and mutations affecting synthesis of these components reduce ability to cause disease. In previous studies we have found that O antigen and the synthesis and function of IcsA are interrelated. This project will study how the O antigens are synthesised and their chain length determined by the Wzz protein, and the Wzz structure in relation to its function will also be characterised. The role played by O antigen in intracellular motility will be studied to determine the mechanisms involved. Infection of cells and cell free extracts, antibodies, and an enzyme which specifically degrades the O antigen, will be used to study how O antigen affect the interaction between bacteria with human cell proteins. The relationship between O antigen and IcsA function will be studied using monoclonal antibodies raised to IcsA. The effect of LPS on the outer membrane protease IcsP will be investigated, as will the effect of LPS lipid A mutations on O antigen and virulence. These studies will contribute to a better understanding of the biosynthesis of an ubiquitous bacterial cell surface component (O antigen), its function as a virulence factor in bacterial interactions with host cells. This may lead to novel therapeutic strategies to prevent and control Shigellosis and other bacterial infections.