Verger Denis, Bullitt Esther, Hultgren Scott J, Waksman Gabriel
Institute of Structural Molecular Biology, University College London and Birkbeck College, London, United Kingdom.
PLoS Pathog. 2007 May 18;3(5):e73. doi: 10.1371/journal.ppat.0030073.
P pili are important adhesive fibres involved in kidney infection by uropathogenic Escherichia coli strains. P pili are assembled by the conserved chaperone-usher pathway, which involves the PapD chaperone and the PapC usher. During pilus assembly, subunits are incorporated into the growing fiber via the donor-strand exchange (DSE) mechanism, whereby the chaperone's G1 beta-strand that complements the incomplete immunoglobulin-fold of each subunit is displaced by the N-terminal extension (Nte) of an incoming subunit. P pili comprise a helical rod, a tip fibrillum, and an adhesin at the distal end. PapA is the rod subunit and is assembled into a superhelical right-handed structure. Here, we have solved the structure of a ternary complex of PapD bound to PapA through donor-strand complementation, itself bound to another PapA subunit through DSE. This structure provides insight into the structural basis of the DSE reaction involving this important pilus subunit. Using gel filtration chromatography and electron microscopy on a number of PapA Nte mutants, we establish that PapA differs in its mode of assembly compared with other Pap subunits, involving a much larger Nte that encompasses not only the DSE region of the Nte but also the region N-terminal to it.
P菌毛是参与尿路致病性大肠杆菌菌株引起肾脏感染的重要粘附纤维。P菌毛通过保守的伴侣-组装分子途径进行组装，该途径涉及PapD伴侣和PapC组装分子。在菌毛组装过程中，亚基通过供体链交换（DSE）机制整合到正在生长的纤维中，即伴侣蛋白的G1β链与每个亚基不完全的免疫球蛋白折叠互补，被进入的亚基的N端延伸（Nte）取代。P菌毛由螺旋状杆、顶端纤维和远端的粘附素组成。PapA是杆状亚基，组装成右手超螺旋结构。在这里，我们通过供体链互补解析了与PapA结合的PapD三元复合物的结构，其自身通过DSE与另一个PapA亚基结合。该结构为涉及这种重要菌毛亚基的DSE反应的结构基础提供了见解。通过对多个PapA Nte突变体进行凝胶过滤色谱和电子显微镜分析，我们确定PapA与其他Pap亚基相比，其组装模式不同，涉及一个大得多的Nte，它不仅包括Nte的DSE区域，还包括其N端区域。
