School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, 3010, Australia.
Computational Biology and Clinical Informatics, Baker Heart and Diabetes Institute, Melbourne, Victoria, 3004, Australia.
Appl Biochem Biotechnol. 2024 Sep;196(9):6059-6071. doi: 10.1007/s12010-023-04820-3. Epub 2024 Jan 5.
Glycoside hydrolases (GHs) are a diverse group of enzymes that catalyze the hydrolysis of glycosidic bonds. The Carbohydrate-Active enZymes (CAZy) classification organizes GHs into families based on sequence data and function, with fewer than 1% of the predicted proteins characterized biochemically. Consideration of genomic context can provide clues to infer possible enzyme activities for proteins of unknown function. We used the MultiGeneBLAST tool to discover a gene cluster in Marinovum sp., a member of the marine Roseobacter clade, that encodes homologues of enzymes belonging to the sulfoquinovose monooxygenase pathway for sulfosugar catabolism. This cluster lacks a gene encoding a classical family GH31 sulfoquinovosidase candidate, but which instead includes an uncharacterized family GH13 protein (MsGH13) that we hypothesized could be a non-classical sulfoquinovosidase. Surprisingly, recombinant MsGH13 lacks sulfoquinovosidase activity and is a broad-spectrum α-glucosidase that is active on a diverse array of α-linked disaccharides, including maltose, sucrose, nigerose, trehalose, isomaltose, and kojibiose. Using AlphaFold, a 3D model for the MsGH13 enzyme was constructed that predicted its active site shared close similarity with an α-glucosidase from Halomonas sp. H11 of the same GH13 subfamily that shows narrower substrate specificity.
糖苷水解酶（GHs）是一组多样化的酶，能够催化糖苷键的水解。碳水化合物活性酶（CAZy）分类根据序列数据和功能将 GHs 组织成家族，其中只有不到 1%的预测蛋白具有生化特征。考虑基因组背景可以为未知功能的蛋白推断可能的酶活性提供线索。我们使用多基因 BLAST 工具在海洋 Roseobacter 分支的 Marinovum sp. 中发现了一个基因簇，该基因簇编码属于磺基奎诺糖单加氧酶途径的酶的同源物，用于磺基糖的分解代谢。该簇缺乏编码经典家族 GH31 磺基奎诺糖酶候选物的基因，但包含一个未表征的家族 GH13 蛋白（MsGH13），我们假设它可能是非经典的磺基奎诺糖酶。令人惊讶的是，重组 MsGH13 缺乏磺基奎诺糖酶活性，而是一种广谱的α-葡萄糖苷酶，能够作用于多种α-连接的二糖，包括麦芽糖、蔗糖、黑曲霉二糖、海藻糖、异麦芽糖和昆布二糖。使用 AlphaFold，构建了 MsGH13 酶的 3D 模型，预测其活性位点与同一家族 GH13 的 Halomonas sp. H11 的 α-葡萄糖苷酶具有密切的相似性，后者显示出更窄的底物特异性。
