Shen Xing, Saburi Wataru, Gai Zuo-Qi, Komoda Keisuke, Yu Jian, Ojima-Kato Teruyo, Kido Yusuke, Matsui Hirokazu, Mori Haruhide, Yao Min
School of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, People's Republic of China.
Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8689, Japan.
Acta Crystallogr F Struct Biol Commun. 2014 Apr;70(Pt 4):464-6. doi: 10.1107/S2053230X14001940. Epub 2014 Mar 25.
The α-glucosidase HaG from the halophilic bacterium Halomonas sp. strain H11 catalyzes the hydrolysis of the glucosidic linkage at the nonreducing end of α-glucosides, such as maltose and sucrose, to release α-glucose. Based on its amino-acid sequence, this enzyme is classified as a member of glycoside hydrolase family 13. HaG has three unique characteristics: (i) a very narrow substrate specificity, almost exclusively hydrolyzing disaccharides; (ii) activation by monovalent cations, such as K(+), Rb(+), Cs(+) and NH4(+); and (iii) high transfer activity of the glucose moiety to the OH group of low-molecular-weight compounds, including glycerol and 6-gingerol. Crystallographic studies have been performed in order to understand these special features. An expression vector was constructed and recombinant HaG protein was overexpressed, purified and crystallized. A data set to 2.15 Å resolution was collected and processed. The crystal belonged to space group P212121, with unit-cell parameters a = 60.2, b = 119.2, c = 177.2 Å. The structure has been determined by molecular replacement using the isomaltulose synthase PalI as the search model (PDB entry 1m53).
来自嗜盐细菌嗜盐单胞菌属菌株H11的α-葡萄糖苷酶HaG催化α-葡萄糖苷（如麦芽糖和蔗糖）非还原端的糖苷键水解，释放出α-葡萄糖。根据其氨基酸序列，该酶被归类为糖苷水解酶家族13的成员。HaG具有三个独特的特性：（i）底物特异性非常狭窄，几乎只水解二糖；（ii）被单价阳离子（如K⁺、Rb⁺、Cs⁺和NH₄⁺）激活；（iii）葡萄糖部分向包括甘油和6-姜酚在内的低分子量化合物的OH基团具有高转移活性。为了理解这些特殊特征，已进行了晶体学研究。构建了表达载体，重组HaG蛋白被过量表达、纯化并结晶。收集并处理了分辨率为2.15 Å的数据集。该晶体属于空间群P212121，晶胞参数a = 60.2、b = 119.2、c = 177.2 Å。已通过以异麦芽糖合酶PalI作为搜索模型（PDB条目1m53）的分子置换法确定了其结构。
