The Biosynthesis of Lipooligosaccharide from Bacteroides thetaiotaomicron.
The Biosynthesis of Lipooligosaccharide from Bacteroides thetaiotaomicron.
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DOI：
10.1128/mbio.02289-17
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发表时间：
2018-03-13
期刊：
影响因子：
6.4
通讯作者：
Fischbach MA
中科院分区：
文献类型：
--
作者：
Jacobson AN;Choudhury BP;Fischbach MA
脂多糖(LPS)是革兰氏阴性菌外膜外叶的一种细胞相关糖脂，是微生物与宿主相互作用的典型介体。最常见的革兰氏阴性肠道细菌分类群，类杆菌，约占典型西式肠道细胞的50%；这些细胞含有约300000 mg的内毒素，使其成为肠道中含量最高的分子之一。为了了解类杆菌脂多糖的生物学功能，我们已经在类杆菌VPI 5482中鉴定了参与其脂A核心和糖的生物合成的基因，产生了详细描述脂多糖变化形式的突变体，并使用基质辅助激光解吸电离飞行时间质谱仪(MALDI-TOF)来询问这些突变体的分子特征。我们证明，除其他外，多糖似乎没有重复单位，因此该菌株产生脂低聚糖(LOS)，而不是内毒素。这一结果与普通拟杆菌ATCC 8482形成了鲜明对比，通过SDS-PAGE分析，ATCC 8482似乎产生了带有重复单位的内毒素。此外，我们对B.thetaiotaomicron LOS寡糖基因簇的鉴定使我们能够在其他类杆菌物种中识别类似的簇。我们的工作为在寄主定植的背景下建立类杆菌内毒素/LOS的结构-功能关系奠定了基础。人们对组成人类微生物群的细菌物种和基因知之甚少，但对微生物群影响宿主生物学的分子机制知之甚少。众所周知，细菌影响宿主的机制是以内毒素为中心的，内毒素是革兰氏阴性细菌外膜的一种成分。病原菌来源的脂多糖是宿主受体Toll样受体4的有效配体，作为先天免疫反应的一部分，Toll样受体4在感知细菌方面发挥着重要作用。令人费解的是，人类最常见的肠道细菌类杆菌能产生内毒素，但不会引发强烈的促炎反应。以前的工作表明，类杆菌内毒素在结构上不同于病原体来源的内毒素，这给出了解释的大纲。在这里，我们采取下一步，阐明类杆菌内毒素的生物合成途径，并在此过程中产生突变体，这将对了解该分子如何调节宿主免疫反应有很大帮助。
Lipopolysaccharide (LPS), a cell-associated glycolipid that makes up the outer leaflet of the outer membrane of Gram-negative bacteria, is a canonical mediator of microbe-host interactions. The most prevalent Gram-negative gut bacterial taxon, Bacteroides, makes up around 50% of the cells in a typical Western gut; these cells harbor ~300 mg of LPS, making it one of the highest-abundance molecules in the intestine. As a starting point for understanding the biological function of Bacteroides LPS, we have identified genes in Bacteroides thetaiotaomicron VPI 5482 involved in the biosynthesis of its lipid A core and glycan, generated mutants that elaborate altered forms of LPS, and used matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry to interrogate the molecular features of these variants. We demonstrate, inter alia, that the glycan does not appear to have a repeating unit, and so this strain produces lipooligosaccharide (LOS) rather than LPS. This result contrasts with Bacteroides vulgatus ATCC 8482, which by SDS-PAGE analysis appears to produce LPS with a repeating unit. Additionally, our identification of the B. thetaiotaomicron LOS oligosaccharide gene cluster allowed us to identify similar clusters in other Bacteroides species. Our work lays the foundation for developing a structure-function relationship for Bacteroides LPS/LOS in the context of host colonization. Much is known about the bacterial species and genes that make up the human microbiome, but remarkably little is known about the molecular mechanisms through which the microbiota influences host biology. A well-known mechanism by which bacteria influence the host centers around lipopolysaccharide (LPS), a component of the Gram-negative bacterial outer membrane. Pathogen-derived LPS is a potent ligand for host receptor Toll-like receptor 4, which plays an important role in sensing bacteria as part of the innate immune response. Puzzlingly, the most common genus of human gut bacteria, Bacteroides, produces LPS but does not elicit a potent proinflammatory response. Previous work showing that Bacteroides LPS differs structurally from pathogen-derived LPS suggested the outlines of an explanation. Here, we take the next step, elucidating the biosynthetic pathway for Bacteroides LPS and generating mutants in the process that will be of great use in understanding how this molecule modulates the host immune response.