Kutter Stefan, Buhrdorf Renate, Haas Jürgen, Schneider-Brachert Wulf, Haas Rainer, Fischer Wolfgang
Abteilung Bakteriologie, Max von Pettenkofer Institut für Hygiene und Medizinische Mikrobiologie, Ludwig Maximilians Universität, 80336 München, Germany.
J Bacteriol. 2008 Mar;190(6):2161-71. doi: 10.1128/JB.01341-07. Epub 2008 Jan 4.
Type IV secretion systems are possibly the most versatile protein transport systems in gram-negative bacteria, with substrates ranging from small proteins to large nucleoprotein complexes. In many cases, such as the cag pathogenicity island of Helicobacter pylori, genes encoding components of a type IV secretion system have been identified due to their sequence similarities to prototypical systems such as the VirB system of Agrobacterium tumefaciens. The Cag type IV secretion system contains at least 14 essential apparatus components and several substrate translocation and auxiliary factors, but the functions of most components cannot be inferred from their sequences due to the lack of similarities. In this study, we have performed a comprehensive sequence analysis of all essential or auxiliary Cag components, and we have used antisera raised against a subset of components to determine their subcellular localization. The results suggest that the Cag system contains functional analogues to all VirB components except VirB5. Moreover, we have characterized mutual stabilization effects and performed a comprehensive yeast two-hybrid screening for potential protein-protein interactions. Immunoprecipitation studies resulted in identification of a secretion apparatus subassembly at the outer membrane. Combining these data, we provide a first low-resolution model of the Cag type IV secretion apparatus.
IV型分泌系统可能是革兰氏阴性菌中最为通用的蛋白质转运系统，其转运底物范围从小蛋白到大核蛋白复合物。在许多情况下，比如幽门螺杆菌的cag致病岛，由于编码IV型分泌系统组分的基因与诸如根癌土壤杆菌的VirB系统等典型系统具有序列相似性，因而得以被鉴定出来。Cag IV型分泌系统至少包含14种必需的装置组分以及若干底物转运和辅助因子，但是由于缺乏相似性，大多数组分的功能无法从其序列中推断出来。在本研究中，我们对所有必需的或辅助的Cag组分进行了全面的序列分析，并且使用针对一部分组分产生的抗血清来确定它们的亚细胞定位。结果表明，Cag系统包含除VirB5之外所有VirB组分的功能类似物。此外，我们对相互稳定作用进行了表征，并针对潜在的蛋白质-蛋白质相互作用开展了全面的酵母双杂交筛选。免疫沉淀研究鉴定出了在外膜处的一个分泌装置亚组件。综合这些数据，我们提供了Cag IV型分泌装置的首个低分辨率模型。
