Korotkov Konstantin V, Sandkvist Maria
Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, KY 40506.
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109.
EcoSal Plus. 2019 Feb;8(2). doi: 10.1128/ecosalplus.ESP-0034-2018.
The type II secretion system (T2SS) delivers toxins and a range of hydrolytic enzymes, including proteases, lipases, and carbohydrate-active enzymes, to the cell surface or extracellular space of Gram-negative bacteria. Its contribution to survival of both extracellular and intracellular pathogens as well as environmental species of proteobacteria is evident. This dynamic, multicomponent machinery spans the entire cell envelope and consists of a cytoplasmic ATPase, several inner membrane proteins, a periplasmic pseudopilus, and a secretin pore embedded in the outer membrane. Despite the -envelope configuration of the T2S nanomachine, proteins to be secreted engage with the system first once they enter the periplasmic compartment via the Sec or TAT export system. Thus, the T2SS is specifically dedicated to their outer membrane translocation. The many sequence and structural similarities between the T2SS and type IV pili suggest a common origin and argue for a pilus-mediated mechanism of secretion. This minireview describes the structures, functions, and interactions of the individual T2SS components and the general architecture of the assembled T2SS machinery and briefly summarizes the transport and function of a growing list of T2SS exoproteins. Recent advances in cryo-electron microscopy, which have led to an increased understanding of the structure-function relationship of the secretin channel and the pseudopilus, are emphasized.
II型分泌系统（T2SS）将毒素和一系列水解酶，包括蛋白酶、脂肪酶和碳水化合物活性酶，输送到革兰氏阴性菌的细胞表面或细胞外空间。其对细胞外和细胞内病原体以及变形菌门环境物种生存的贡献是显而易见的。这种动态的多组分机制跨越整个细胞包膜，由一个细胞质ATP酶、几个内膜蛋白、一个周质假菌毛和一个嵌入外膜的分泌素孔组成。尽管T2S纳米机器具有跨包膜结构，但待分泌的蛋白质一旦通过Sec或TAT输出系统进入周质区室，就会首先与该系统结合。因此，T2SS专门负责它们向外膜的转运。T2SS与IV型菌毛之间的许多序列和结构相似性表明它们有共同的起源，并支持菌毛介导的分泌机制。这篇小型综述描述了各个T2SS组件的结构、功能和相互作用以及组装好的T2SS机制的总体架构，并简要总结了越来越多的T2SS外蛋白的转运和功能。强调了低温电子显微镜的最新进展，这些进展增进了我们对分泌素通道和假菌毛结构-功能关系的理解。
