加拿大英属哥伦比亚大学Stephen G. Withers课题组发现细菌中糖类分解的另一种广泛特异性途径。相关论文于2024年6月19日在线发表在《自然》杂志上。

研究人员描述了利用一种能选择性鉴定非柯什兰糖苷酶活性的检测方法对人类肠道微生物组元基因组文库进行的大规模筛选。通过这种方法，研究人员发现了一组底物特异性极强的酶，并从机理和结构上对这些酶进行了深入研究。这些酶不仅能打破具有α和β立体化学和多种连接性的糖苷键，还能切割标准糖苷酶不能水解的底物。

这些底物包括硫代糖苷，如植物中的葡萄糖苷酸盐，以及阿卡波糖等药物的假糖苷键。这些酶通过不同的水解机制实现水解，其中包括氧化/还原和消除/水合步骤，每个步骤都由酶模块催化，在许多情况下，这些酶模块可以在不同生物体和底物类别之间互换。这些酶的同源物出现在与肠道微生物群和身体其他部位以及土壤和海洋等其他环境相关的革兰氏阳性和革兰氏阴性细菌中。

作为细菌碳水化合物新陈代谢的一部分，这种替代性分步机制似乎构成了糖降解的主要途径，但这种途径在很大程度上尚未被认识到，但却非常丰富。

据悉，迄今为止，绝大多数糖苷酶都遵循“科什兰”机制的一种变体，通过取代反应水解糖苷键。

附：英文原文

Title: An alternative broad-specificity pathway for glycan breakdown in bacteria

Author: Nasseri, Seyed Amirhossein, Lazarski, Aleksander C., Lemmer, Imke L., Zhang, Chloe Y., Brencher, Eva, Chen, Hong-Ming, Sim, Lyann, Panwar, Deepesh, Betschart, Leo, Worrall, Liam J., Brumer, Harry, Strynadka, Natalie C. J., Withers, Stephen G.

Issue&Volume: 2024-06-19

Abstract: The vast majority of glycosidases characterized to date follow one of the variations of the ‘Koshland’ mechanisms1 to hydrolyse glycosidic bonds through substitution reactions. Here we describe a large-scale screen of a human gut microbiome metagenomic library using an assay that selectively identifies non-Koshland glycosidase activities2. Using this, we identify a cluster of enzymes with extremely broad substrate specificities and thoroughly characterize these, mechanistically and structurally. These enzymes not only break glycosidic linkages of both α and β stereochemistry and multiple connectivities, but also cleave substrates that are not hydrolysed by standard glycosidases. These include thioglycosides, such as the glucosinolates from plants, and pseudoglycosidic bonds of pharmaceuticals such as acarbose. This is achieved through a distinct mechanism of hydrolysis that involves oxidation/reduction and elimination/hydration steps, each catalysed by enzyme modules that are in many cases interchangeable between organisms and substrate classes. Homologues of these enzymes occur in both Gram-positive and Gram-negative bacteria associated with the gut microbiome and other body parts, as well as other environments, such as soil and sea. Such alternative step-wise mechanisms appear to constitute largely unrecognized but abundant pathways for glycan degradation as part of the metabolism of carbohydrates in bacteria.

DOI: 10.1038/s41586-024-07574-y

Source: https://www.nature.com/articles/s41586-024-07574-y