Structural basis for nutrient acquisition by dominant members of the human gut microbiota.
Structural basis for nutrient acquisition by dominant members of the human gut microbiota.
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DOI：
10.1038/nature20828
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发表时间：
2017-01-19
期刊：
影响因子：
64.8
通讯作者：
van den Berg B
中科院分区：
文献类型：
--
作者：
Glenwright AJ;Pothula KR;Bhamidimarri SP;Chorev DS;Baslé A;Firbank SJ;Zheng H;Robinson CV;Winterhalter M;Kleinekathöfer U;Bolam DN;van den Berg B
人体大肠中存在着密度极高的微生物，统称为结肠微生物群，对人体健康和营养起着重要作用。来自占优势的革兰氏阴性菌门拟杆菌的微生物群成员的存活取决于它们降解不能被宿主代谢的膳食聚糖的能力。编码参与特定聚糖降解的蛋白质的基因被组织成共调节多糖利用位点（普尔斯）。原型PUL已被命名为Sus，用于淀粉利用系统，并由7种蛋白质组成，命名为SusA-G。聚糖降解主要发生在细胞内，并且关键地依赖于由细胞外SusD样脂蛋白和整合的膜SusC样TonB依赖性转运蛋白（TBDT）组成的外膜（OM）蛋白复合物对寡糖的输入。伴侣SusD样脂蛋白的存在是区分SusC样蛋白与先前表征的TBDT的主要差异。许多测序的肠道拟杆菌属编码超过100个C/D对，其中大部分具有未知的功能和底物特异性。中心的，未解决的问题是如何由SusD蛋白的细胞外底物结合耦合到OM通道通过其同源的SusC转运。在这里，我们提出了两个功能不同的SusCD复合物纯化多形拟杆菌的X-射线晶体结构，并推导出一个通用的模型为基板易位。SusC转运蛋白形成同源二聚体，每个β-桶原聚体被SusD紧紧地封端。配体在SusCD界面结合在一个大的溶剂排除腔。分子动力学模拟和单通道电生理学揭示了一种“踏板箱”机制，其中SusD在没有配体的情况下以铰链样的方式远离SusC，将底物结合位点暴露于细胞外环境。我们的研究结果提供了微生物组成员OM营养输入的机制见解，这对于理解人类-微生物组共生具有重要意义。
The human large intestine is populated by an extremely high density of microorganisms, collectively termed the colonic microbiota, which plays an important role in human health and nutrition. The survival of microbiota members from the dominant Gram-negative phylum Bacteroidetes depends on their ability to degrade dietary glycans that cannot be metabolised by the host. The genes encoding proteins involved in the degradation of specific glycans are organised into co-regulated polysaccharide utilisation loci (PULs). The archetypal PUL has been named Sus, for starch utilisation system, and consists of 7 proteins named SusA-G. Glycan degradation occurs mainly intracellularly and depends critically on the import of oligosaccharides by an outer membrane (OM) protein complex composed of an extracellular SusD-like lipoprotein and an integral membrane SusC-like TonB-dependent transporter (TBDT). The presence of the partner SusD-like lipoprotein is the major difference that distinguishes SusC-like proteins from previously characterised TBDTs. Many sequenced gut Bacteroides spp encode over 100 C/D pairs, with the large majority of them having unknown functions and substrate specificities. The central, unresolved question is how extracellular substrate binding by SusD proteins is coupled to OM passage via their cognate SusC transporter. Here we present X-ray crystal structures of two functionally distinct SusCD complexes purified from Bacteroides thetaiotaomicron and derive a general model for substrate translocation. The SusC transporters form homodimers, with each β-barrel protomer tightly capped by the SusD. Ligands are bound at the SusCD interface in a large solvent-excluded cavity. Molecular dynamics simulations and single channel electrophysiology reveal a "pedal bin" mechanism in which SusD moves away from SusC in a hinge-like fashion in the absence of ligand to expose the substrate binding site to the extracellular milieu. Our results provide mechanistic insights into OM nutrient import by members of the microbiota, which is of major significance for understanding the human-microbiota symbiosis.