Institute of Biochemistry, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
Institute of Genetics and Microbiology, University of Paris-Sud, Orsay, France.
Microbiol Spectr. 2019 Mar;7(2). doi: 10.1128/microbiolspec.PSIB-0003-2018.
Type I secretion systems (T1SS) are widespread in Gram-negative bacteria, especially in pathogenic bacteria, and they secrete adhesins, iron-scavenger proteins, lipases, proteases, or pore-forming toxins in the unfolded state in one step across two membranes without any periplasmic intermediate into the extracellular space. The substrates of T1SS are in general characterized by a C-terminal secretion sequence and nonapeptide repeats, so-called GG repeats, located N terminal to the secretion sequence. These GG repeats bind Ca ions in the extracellular space, which triggers folding of the entire protein. Here we summarize our current knowledge of how Gram-negative bacteria secrete these substrates, which can possess a molecular mass of up to 1,500 kDa. We also describe recent findings that demonstrate that the absence of periplasmic intermediates, the "classic" mode of action, does not hold true for all T1SS and that we are beginning to realize modifications of a common theme.
I 型分泌系统（T1SS）广泛存在于革兰氏阴性菌中，尤其是在病原菌中，它们能一步跨膜将未折叠状态的黏附素、铁载体蛋白、脂肪酶、蛋白酶或孔形成毒素分泌到细胞外，而无需任何周质中间产物。T1SS 的底物通常具有 C 端分泌序列和位于分泌序列 N 端的九肽重复序列，即所谓的 GG 重复序列。这些 GG 重复序列结合细胞外空间中的 Ca 离子，从而触发整个蛋白质的折叠。在这里，我们总结了目前对革兰氏阴性菌分泌这些底物的认识，这些底物的分子量可达 1500 kDa 左右。我们还描述了最近的发现，证明缺乏周质中间产物（“经典”作用模式）并不适用于所有 T1SS，并且我们开始意识到常见主题的修饰。
