Engineering Research Center of Sustainable Development and Utilization of Biomass Energy, Ministry of Education , Yunnan Normal University , Kunming 650500 , People's Republic of China.
College of Life Sciences , Yunnan Normal University , No. 768 Juxian Street , Kunming 650500 , People's Republic of China.
J Agric Food Chem. 2019 Mar 20;67(11):3220-3228. doi: 10.1021/acs.jafc.9b00027. Epub 2019 Mar 12.
β-1,2-Xylosidase activity has not been recorded as an EC subsubclass. In this study, phylogenetic analysis and multiple sequence alignments revealed that characterized β-xylosidases of glycoside hydrolase family (GH) 39 were classified into the same subgroup with conserved amino acid residue positions participating in substrate recognition. Protein-ligand docking revealed that seven of these positions were probably essential to bind xylose-glucose, which is linked by a β-1,2-glycosidic bond. Amino acid residues in five of the seven positions are invariant, while those in two of the seven positions are variable with low frequency. Both the wild-type β-xylosidase rJB13GH39 and its mutants with mutation at the two positions exhibited β-1,2-xylosidase activity, as they hydrolyzed o-nitrophenyl-β-d-xylopyranoside and transformed notoginsenosides R and R to ginsenosides Rg and Rh, respectively. The results suggest that all of these characterized GH 39 β-xylosidases probably show β-1,2-xylosidase activity, which should be assigned an EC number with these β-xylosidases as representatives.
β-1,2-木糖苷酶活性尚未被记录为 EC 亚类。在这项研究中，系统发育分析和多重序列比对表明，糖苷水解酶家族 (GH) 39 中的特征性β-木糖苷酶被归类为具有保守氨基酸残基位置的相同亚组，这些位置参与了底物识别。蛋白-配体对接表明，这七个位置可能对结合通过β-1,2-糖苷键连接的木糖-葡萄糖是必需的。这七个位置中的五个位置的氨基酸残基是不变的，而这七个位置中的两个位置的氨基酸残基是可变的，频率较低。野生型 rJB13GH39 β-木糖苷酶及其在两个位置发生突变的突变体均表现出β-1,2-木糖苷酶活性，因为它们水解邻硝基苯-β-d-木吡喃糖苷，并分别将人参皂苷 R 和 R 转化为人参皂苷 Rg 和 Rh。结果表明，所有这些特征性的 GH 39 β-木糖苷酶可能都表现出β-1,2-木糖苷酶活性，应该为其分配一个 EC 编号，以这些β-木糖苷酶作为代表。
