Structural Insight into How Bacteria Prevent Interference between Multiple Divergent Type IV Secretion Systems.
Structural Insight into How Bacteria Prevent Interference between Multiple Divergent Type IV Secretion Systems.
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DOI：
10.1128/mbio.01867-15
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发表时间：
2015-12-08
期刊：
影响因子：
6.4
通讯作者：
Pulliainen AT
中科院分区：
文献类型：
--
作者：
Gillespie JJ;Phan IQ;Scheib H;Subramanian S;Edwards TE;Lehman SS;Piitulainen H;Rahman MS;Rennoll-Bankert KE;Staker BL;Taira S;Stacy R;Myler PJ;Azad AF;Pulliainen AT
原核生物使用IV型分泌系统（T4 SS）来易位底物（例如，核蛋白、DNA和蛋白质）和/或精细的表面结构（即，皮利或粘附素）。细菌基因组可以编码多个T4 SS，例如，在某些巴尔通体属物种中存在三种功能不同的T4 SS（vir、vbh和trw）。在一个独特的情况下，大多数立克次体物种编码T4 SS（rvh）丰富的基因重复。在单个基因组内，类似T4 SS蛋白组分的跨系统互换性的进化和功能影响仍然知之甚少。为了深入了解跨系统可移植性，我们分析了T4 SS通道蛋白的VirB 8家族。三个VirB 8和两个TrwG巴尔通体蛋白的晶体结构显示高度保守的C-末端周质结构域折叠和二聚化接口，尽管巨大的序列差异。这意味着在功能性T4 SS的组装中VirB 8组件的显著结构约束。VirB 8/TrwG异源二聚体，通过细菌双杂交测定和分子建模确定，表明trw和vir系统的差异表达可能是VirB 8-TrwG亲和性的障碍。我们还确定了伤寒立克次体RvhB 8-II的晶体结构，并模拟了其共表达的趋异蛋白RvhB 8-I。值得注意的是，虽然RvhB 8-I二聚化并且在结构上类似于其他VirB 8蛋白，但RvhB 8-II二聚体界面基本上偏离其他VirB 8结构，潜在地阻止RvhB 8-I/RvhB 8-II异源二聚化。对于RVH T4 SS，不同VirB 8旁系同源物的进化意味着在其他T4 SS中未知的功能多样化。总的来说，我们的数据确定了两个不同的限制（时空巴尔通体trw和vir T4 SS和结构rvh T4 SS），介导的功能，多个不同的T4 SS在一个单一的细菌。在正确的时间和正确的细胞位置组装多蛋白复合物对任何生物体来说都是一项至关重要的任务。在这方面，表达多种类似的IV型分泌系统（T4 SS）的细菌，每个系统由大约12种不同的成分组成，面临着压倒性的复杂性。我们在这里的工作提出了第一个结构调查的因素，调节多个T4 SS的维护在一个单一的细菌。结构数据表明，T4 SS表达细菌依赖于两种策略来防止跨系统可互换性：（i）表达的严格时间调节或（ii）T4 SS组分的快速多样化。T4 SS是理想的药物靶标，前提是真核生物中没有类似的对应物。靶向跨系统相容性障碍的药物（即，调节因子）可能会使离散系统的结构和功能独立性失调，可能会产生干扰，阻止它们在细菌感染过程中的有效协调。
Prokaryotes use type IV secretion systems (T4SSs) to translocate substrates (e.g., nucleoprotein, DNA, and protein) and/or elaborate surface structures (i.e., pili or adhesins). Bacterial genomes may encode multiple T4SSs, e.g., there are three functionally divergent T4SSs in some Bartonella species (vir, vbh, and trw). In a unique case, most rickettsial species encode a T4SS (rvh) enriched with gene duplication. Within single genomes, the evolutionary and functional implications of cross-system interchangeability of analogous T4SS protein components remains poorly understood. To lend insight into cross-system interchangeability, we analyzed the VirB8 family of T4SS channel proteins. Crystal structures of three VirB8 and two TrwG Bartonella proteins revealed highly conserved C-terminal periplasmic domain folds and dimerization interfaces, despite tremendous sequence divergence. This implies remarkable structural constraints for VirB8 components in the assembly of a functional T4SS. VirB8/TrwG heterodimers, determined via bacterial two-hybrid assays and molecular modeling, indicate that differential expression of trw and vir systems is the likely barrier to VirB8-TrwG interchangeability. We also determined the crystal structure of Rickettsia typhi RvhB8-II and modeled its coexpressed divergent paralog RvhB8-I. Remarkably, while RvhB8-I dimerizes and is structurally similar to other VirB8 proteins, the RvhB8-II dimer interface deviates substantially from other VirB8 structures, potentially preventing RvhB8-I/RvhB8-II heterodimerization. For the rvh T4SS, the evolution of divergent VirB8 paralogs implies a functional diversification that is unknown in other T4SSs. Collectively, our data identify two different constraints (spatiotemporal for Bartonella trw and vir T4SSs and structural for rvh T4SSs) that mediate the functionality of multiple divergent T4SSs within a single bacterium. Assembly of multiprotein complexes at the right time and at the right cellular location is a fundamentally important task for any organism. In this respect, bacteria that express multiple analogous type IV secretion systems (T4SSs), each composed of around 12 different components, face an overwhelming complexity. Our work here presents the first structural investigation on factors regulating the maintenance of multiple T4SSs within a single bacterium. The structural data imply that the T4SS-expressing bacteria rely on two strategies to prevent cross-system interchangeability: (i) tight temporal regulation of expression or (ii) rapid diversification of the T4SS components. T4SSs are ideal drug targets provided that no analogous counterparts are known from eukaryotes. Drugs targeting the barriers to cross-system interchangeability (i.e., regulators) could dysregulate the structural and functional independence of discrete systems, potentially creating interference that prevents their efficient coordination throughout bacterial infection.