Extended loop region of Hcp1 is critical for the assembly and function of type VI secretion system in Burkholderia pseudomallei.
Extended loop region of Hcp1 is critical for the assembly and function of type VI secretion system in Burkholderia pseudomallei.
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DOI：
10.1038/srep08235
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发表时间：
2015-02-04
影响因子：
4.6
通讯作者：
Gan YH
中科院分区：
文献类型：
--
作者：
Lim YT;Jobichen C;Wong J;Limmathurotsakul D;Li S;Chen Y;Raida M;Srinivasan N;MacAry PA;Sivaraman J;Gan YH
VI型分泌系统簇1（T6 SS 1）对于类鼻疽伯克霍尔德菌的发病机制是必需的，类鼻疽是热带地方性疾病的病原体。在宿主细胞内，B.类鼻疽逃逸到胞质溶胶中并通过T6 SS 1，诱导多核巨细胞（MNGC）形成，这被认为对于细菌细胞到细胞的传播是重要的。溶血素共调节蛋白（Hcp）既是T6 SS底物，也是T6 SS分泌管的一部分。我们的结构研究表明，Hcp 1形成六聚体环类似于其他HCP同系物，但有一个延长的环（Asp 40-Arg 56），偏离显着的位置相比，其他HCP结构，并可能作为一个关键的接触点相邻的六聚体环之间。当环内的两个残基发生突变时，突变蛋白不能堆叠为十二聚体，表明有缺陷的管组装。此外，用含有这些hcp 1残基的原位取代的细菌突变体感染废除了感染细胞内的Hcp 1分泌和MNGC形成。我们进一步表明，HCP具有优先结合抗原呈递细胞表面的能力，这可能有助于其免疫原性诱导类鼻疽患者中观察到的高滴度抗体。
The Type VI Secretion System cluster 1 (T6SS1) is essential for the pathogenesis of Burkholderia pseudomallei, the causative agent of melioidosis, a disease endemic in the tropics. Inside host cells, B. pseudomallei escapes into the cytosol and through T6SS1, induces multinucleated giant cell (MNGC) formation that is thought to be important for bacterial cell to cell spread. The hemolysin-coregulated protein (Hcp) is both a T6SS substrate, as well as postulated to form part of the T6SS secretion tube. Our structural study reveals that Hcp1 forms hexameric rings similar to the other Hcp homologs but has an extended loop (Asp40-Arg56) that deviates significantly in position compared to other Hcp structures and may act as a key contact point between adjacent hexameric rings. When two residues within the loop were mutated, the mutant proteins were unable to stack as dodecamers, suggesting defective tube assembly. Moreover, infection with a bacterial mutant containing in situ substitution of these hcp1 residues abolishes Hcp1 secretion inside infected cells and MNGC formation. We further show that Hcp has the ability to preferentially bind to the surface of antigen-presenting cells, which may contribute to its immunogenicity in inducing high titers of antibodies seen in melioidosis patients.