Bacterial Pathogenesis Group, Institut de Biologie Structurale (IBS), Université Grenoble I, France.
J Mol Biol. 2011 Oct 14;413(1):236-46. doi: 10.1016/j.jmb.2011.07.043. Epub 2011 Aug 4.
Pseudomonas aeruginosa is an opportunistic human pathogen that employs a finely tuned type III secretion system (T3SS) to inject toxins directly into the cytoplasm of target cells. ExsB is a 15.6-kDa protein encoded in a T3SS transcription regulation operon that displays high sequence similarity to YscW, a lipoprotein from Yersinia spp. whose genetic neighborhood also involves a transcriptional regulator, and has been shown to play a role in the stabilization of the outer membrane ring of the T3SS. Here, we show that ExsB is expressed in P. aeruginosa upon induction of the T3SS, and subcellular fractionation studies reveal that it is associated with the outer membrane. The high-resolution crystal structure of ExsB shows that it displays a compact β-sandwich fold with interdependent β-sheets. ExsB possesses a large patch of basic residues that could play a role in membrane recognition, and its structure is distinct from that of MxiM, a lipoprotein involved in secretin stabilization in Shigella, as well as from those of Pil lipoproteins involved in pilus biogenesis. These results reveal that small lipoproteins involved in formation of the outer membrane secretin ring display clear structural differences that may be related to the different functions they play in these systems.
铜绿假单胞菌是一种机会性人类病原体，它利用精细调节的 III 型分泌系统（T3SS）将毒素直接注射到靶细胞的细胞质中。ExsB 是编码在 T3SS 转录调控操纵子中的 15.6kDa 蛋白，与 YscW 具有高度序列相似性，YscW 是耶尔森氏菌属的一种脂蛋白，其遗传邻域还涉及转录调节因子，并已被证明在 T3SS 外膜环的稳定中发挥作用。在这里，我们表明 ExsB 在 T3SS 诱导时在铜绿假单胞菌中表达，并且亚细胞分级分离研究表明它与外膜相关。ExsB 的高分辨率晶体结构表明它显示出紧凑的β-夹心折叠，具有相互依赖的β-片层。ExsB 具有一个大的碱性残基区域，可能在膜识别中发挥作用，其结构与 Shigella 中参与分泌稳定的脂蛋白 MxiM 以及与参与菌毛生物发生的 Pil 脂蛋白的结构不同。这些结果表明，参与外膜分泌环形成的小脂蛋白显示出明显的结构差异，这可能与它们在这些系统中发挥的不同功能有关。
