Department of Cellular Microbiology, Max-Planck-Institute for Infection Biology, 10117 Berlin, Germany.
J Biol Chem. 2010 Dec 17;285(51):39965-75. doi: 10.1074/jbc.M110.135616. Epub 2010 Oct 11.
Type III secretion systems (TTSSs) utilized by enteropathogenic bacteria require the presence of small, acidic virulence-associated chaperones for effective host cell infection. We adopted a combination of biochemical and cellular techniques to define the chaperone binding domains (CBDs) in the translocators IpaB and IpaC associated with the chaperone IpgC from Shigella flexneri. We identified a novel CBD in IpaB and furthermore precisely mapped the boundaries of the CBDs in both translocator proteins. In IpaC a single binding domain associates with IpgC. In IpaB, we show that the binding of the newly characterized CBD is essential in maintaining the ternary arrangement of chaperone-translocator complex. This hitherto unknown function is reflected in the co-crystal structure as well, with an IpgC dimer bound to an IpaB fragment comprising both CBDs. Moreover, in the absence of this novel CBD the IpaB/IpgC complex aggregates. This dual-recognition of a domain in the protein by the chaperone in facilitating the correct chaperone-substrate organization describes a new function for the TTSS associated chaperone-substrate complexes.
III 型分泌系统（TTSSs）被肠致病性细菌利用，需要存在小的酸性毒力相关伴侣蛋白，以实现有效的宿主细胞感染。我们采用了生化和细胞技术的组合，来定义与志贺氏菌属的 IpgC 相关的易位蛋白 IpaB 和 IpaC 中的伴侣蛋白结合域（CBD）。我们在 IpaB 中鉴定出一个新的 CBD，并进一步精确地绘制了两个易位蛋白的 CBD 边界。在 IpaC 中，一个结合域与 IpgC 结合。在 IpaB 中，我们表明新表征的 CBD 的结合对于维持伴侣蛋白-易位蛋白复合物的三元排列是必需的。这种迄今为止未知的功能在共结晶结构中也得到了反映，其中 IpgC 二聚体与包含两个 CBD 的 IpaB 片段结合。此外，在没有这个新 CBD 的情况下，IpaB/IpgC 复合物会聚集。这种伴侣蛋白通过识别蛋白中的一个域来促进正确的伴侣蛋白-底物组织，描述了与 TTSS 相关的伴侣蛋白-底物复合物的一个新功能。
