Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia.
PLoS Pathog. 2013 Jan;9(1):e1003117. doi: 10.1371/journal.ppat.1003117. Epub 2013 Jan 10.
The Type II Secretion System (T2SS) is a molecular machine that drives the secretion of fully-folded protein substrates across the bacterial outer membrane. A key element in the machinery is the secretin: an integral, multimeric outer membrane protein that forms the secretion pore. We show that three distinct forms of T2SSs can be distinguished based on the sequence characteristics of their secretin pores. Detailed comparative analysis of two of these, the Klebsiella-type and Vibrio-type, showed them to be further distinguished by the pilotin that mediates their transport and assembly into the outer membrane. We have determined the crystal structure of the novel pilotin AspS from Vibrio cholerae, demonstrating convergent evolution wherein AspS is functionally equivalent and yet structurally unrelated to the pilotins found in Klebsiella and other bacteria. AspS binds to a specific targeting sequence in the Vibrio-type secretins, enhances the kinetics of secretin assembly, and homologs of AspS are found in all species of Vibrio as well those few strains of Escherichia and Shigella that have acquired a Vibrio-type T2SS.
II 型分泌系统（T2SS）是一种分子机器，可驱动完全折叠的蛋白质底物穿过细菌外膜分泌。该机器的一个关键元件是分泌孔道蛋白：一种整合的、多聚体的外膜蛋白，形成分泌孔道。我们表明，根据其分泌孔道的序列特征，可以区分出三种不同形式的 T2SS。对其中两种（克雷伯氏菌型和弧菌型）进行的详细比较分析表明，介导它们运输和组装到外膜的 Pilin 进一步区分了它们。我们已经确定了来自霍乱弧菌的新型 Pilin AspS 的晶体结构，证明了趋同进化，其中 AspS 在功能上等效，但在结构上与克雷伯氏菌和其他细菌中的 Pilin 无关。AspS 结合到弧菌型分泌孔道中的特定靶向序列，增强了分泌孔道组装的动力学，并且 AspS 的同源物存在于所有弧菌物种中，以及少数获得弧菌型 T2SS 的大肠杆菌和志贺氏菌菌株中。
