The Rickettsia type IV secretion system: unrealized complexity mired by gene family expansion
The Rickettsia type IV secretion system: unrealized complexity mired by gene family expansion
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DOI：
10.1093/femspd/ftw058
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发表时间：
2016-08-01
影响因子：
3.3
通讯作者：
Azad, Abdu F.
中科院分区：
文献类型：
--
作者：
Gillespie, Joseph J.;Phan, Isabelle Q. H.;Azad, Abdu F.
许多原核生物利用IV型分泌系统（T4 SS）将底物（例如核蛋白、DNA、蛋白质）跨细胞被膜移位，和/或精细化表面结构（即皮利或粘附素）。在八种不同的T4 SS类别中，P-T4 SS以根癌农杆菌vir T4 SS为代表，其由12种支架组分（VirB 1-VirB 11，VirD 4）组成。虽然大多数P-T4 SS包括所有12种Vir蛋白，但有些P-T4 SS与vir原型的不同之处在于含有与Vir蛋白不类似的额外支架成分或缺乏一种或多种Vir蛋白。在特殊情况下，立克次体vir同源物（rvh）P-T4 SS包括前所未有的基因家族扩展。rvh包含三个基因重复家族（rvhB 9、rvhB 8、rvhB 4）：RvhB 9，8，4-I相对于其他P-T4 SS中的等同物是保守的，而RvhB 9，8，4-II已经进化出与其他同源物基本上偏离的非典型特征。此外，rvh包含五个VirB 6样基因（rvhB 6a-e），它们串联排列并包含大的N末端和C末端延伸。我们在此的工作集中在rvh基因家族扩展所支持的复杂性。此外，我们描述了一个RvhB 10插入，这发生在一个区域，形成T4 SS孔。这些奇怪的属性RVH的结构和功能的意义进行评估，揭示了一个高度复杂的T4 SS。
Many prokaryotes utilize type IV secretion systems (T4SSs) to translocate substrates (e.g. nucleoprotein, DNA, protein) across the cell envelope, and/or to elaborate surface structures (i.e. pili or adhesins). Among eight distinct T4SS classes, P-T4SSs are typified by the Agrobacterium tumefaciens vir T4SS, which is comprised of 12 scaffold components (VirB1-VirB11, VirD4). While most P-T4SSs include all 12 Vir proteins, some differ from the vir archetype by either containing additional scaffold components not analogous to Vir proteins or lacking one or more of the Vir proteins. In a special case, the Rickettsiales vir homolog (rvh) P-T4SS comprises unprecedented gene family expansion. rvh contains three families of gene duplications (rvhB9, rvhB8, rvhB4): RvhB9,8,4-I are conserved relative to equivalents in other P-T4SSs, while RvhB9,8,4-II have evolved atypical features that deviate substantially from other homologs. Furthermore, rvh contains five VirB6-like genes (rvhB6a-e), which are tandemly arrayed and contain large N- and C-terminal extensions. Our work herein focuses on the complexity underpinned by rvh gene family expansion. Furthermore, we describe an RvhB10 insertion, which occurs in a region that forms the T4SS pore. The significance of these curious properties to rvh structure and function is evaluated, shedding light on a highly complex T4SS.