Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada; Department of Biochemistry and Molecular Biology, The Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada.
Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada.
J Biol Chem. 2021 Jan-Jun;296:100415. doi: 10.1016/j.jbc.2021.100415. Epub 2021 Feb 13.
Complex glycans that evade our digestive system are major nutrients that feed the human gut microbiota (HGM). The prevalence of Bacteroidetes in the HGM of populations worldwide is engendered by the evolution of polysaccharide utilization loci (PULs), which encode concerted protein systems to utilize the myriad complex glycans in our diets. Despite their crucial roles in glycan recognition and transport, cell-surface glycan-binding proteins (SGBPs) remained understudied cogs in the PUL machinery. Here, we report the structural and biochemical characterization of a suite of SGBP-A and SGBP-B structures from three syntenic β(1,3)-glucan utilization loci (1,3GULs) from Bacteroides thetaiotaomicron (Bt), Bacteroides uniformis (Bu), and B. fluxus (Bf), which have varying specificities for distinct β-glucans. Ligand complexes provide definitive insight into β(1,3)-glucan selectivity in the HGM, including structural features enabling dual β(1,3)-glucan/mixed-linkage β(1,3)/β(1,4)-glucan-binding capability in some orthologs. The tertiary structural conservation of SusD-like SGBPs-A is juxtaposed with the diverse architectures and binding modes of the SGBPs-B. Specifically, the structures of the trimodular BtSGBP-B and BuSGBP-B revealed a tandem repeat of carbohydrate-binding module-like domains connected by long linkers. In contrast, BfSGBP-B comprises a bimodular architecture with a distinct β-barrel domain at the C terminus that bears a shallow binding canyon. The molecular insights obtained here contribute to our fundamental understanding of HGM function, which in turn may inform tailored microbial intervention therapies.
逃避我们消化系统的复杂糖是主要的营养物质，为人类肠道微生物群（HGM）提供营养。在全球人群的 HGM 中，拟杆菌门的流行是由多糖利用基因座（PUL）的进化引起的，这些基因座编码协同蛋白系统，以利用我们饮食中的无数复杂糖。尽管它们在糖识别和运输中起着至关重要的作用，但细胞表面糖结合蛋白（SGBP）仍然是 PUL 机械中的研究不足的关键部件。在这里，我们报告了来自三个共生β（1,3）-葡聚糖利用基因座（1,3GUL）的一系列 SGBP-A 和 SGBP-B 结构的结构和生化特征，这些结构来自双歧杆菌（Bt），均匀双歧杆菌（Bu）和 B. 通量（Bf），它们对不同的β-葡聚糖具有不同的特异性。配体复合物为 HGM 中的β（1,3）-葡聚糖选择性提供了明确的见解，包括使某些同源物具有双重β（1,3）-葡聚糖/混合链接β（1,3）/β（1,4）-葡聚糖结合能力的结构特征。SusD 样 SGBP-A 的三级结构保守性与 SGBP-B 的不同结构和结合模式并列。具体而言，BtSGBP-B 和 BuSGBP-B 的三模块结构揭示了通过长接头连接的碳水化合物结合模块样结构域的串联重复。相比之下，BfSGBP-B 由双模块结构组成，C 末端具有独特的β-桶结构域，具有浅的结合峡谷。此处获得的分子见解有助于我们对 HGM 功能的基本理解，这反过来又可能为定制的微生物干预疗法提供信息。
