Jaumouillé Valentin, Francetic Olivera, Sansonetti Philippe J, Tran Van Nhieu Guy
Department of Cell Biology and Infections, Unité de Pathogénie Microbienne Moléculaire, Institut Pasteur, Paris, France.
EMBO J. 2008 Jan 23;27(2):447-57. doi: 10.1038/sj.emboj.7601976. Epub 2008 Jan 10.
Type III secretion (T3S) systems are largely used by pathogenic gram-negative bacteria to inject multiple effectors into eukaryotic cells. Upon cell contact, these bacterial microinjection devices insert two T3S substrates into host cell membranes, forming a so-called 'translocon' that is required for targeting of type III effectors in the cell cytosol. Here, we show that secretion of the translocon component IpaC of invasive Shigella occurs at the level of one bacterial pole during cell invasion. Using IpaC fusions with green fluorescent protein variants (IpaCi), we show that the IpaC cytoplasmic pool localizes at an old or new bacterial pole, where secretion occurs upon T3S activation. Deletions in ipaC identified domains implicated in polar localization. Only polar IpaCi derivatives inhibited T3S, while IpaCi fusions with diffuse cytoplasmic localization had no detectable effect on T3S. Moreover, the deletions that abolished polar localization led to secretion defects when introduced in ipaC. These results indicate that cytoplasmic polar localization directs secretion of IpaC at the pole of Shigella, and may represent a mandatory step for T3S.
III型分泌（T3S）系统主要被致病性革兰氏阴性细菌用于将多种效应蛋白注入真核细胞。在细胞接触时，这些细菌微注射装置将两种T3S底物插入宿主细胞膜，形成一种所谓的“转运孔”，这是III型效应蛋白靶向细胞胞质溶胶所必需的。在这里，我们表明侵袭性志贺氏菌的转运孔成分IpaC在细胞入侵期间在一个细菌极的水平上分泌。使用IpaC与绿色荧光蛋白变体的融合体（IpaCi），我们表明IpaC细胞质库定位于旧的或新的细菌极，在T3S激活时在此处发生分泌。ipaC中的缺失鉴定出了与极性定位有关的结构域。只有极性IpaCi衍生物抑制T3S，而具有弥漫性细胞质定位的IpaCi融合体对T3S没有可检测到的影响。此外，当引入ipaC中时，消除极性定位的缺失导致分泌缺陷。这些结果表明细胞质极性定位指导IpaC在志贺氏菌极的分泌，并且可能代表T3S的一个必需步骤。
