Watanabe Risa, Arimura Yasuhiro, Ishii Yoshitaka, Kirimura Kohtaro
Department of Applied Chemistry, Faculty of Science and Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo, 169-8555, Japan.
Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo, 162-8480, Japan.
Biochem Biophys Res Commun. 2020 Jun 4;526(3):580-585. doi: 10.1016/j.bbrc.2020.03.109. Epub 2020 Apr 1.
The α-glucosyl transfer enzyme XgtA is a novel type α-Glucosidase (EC 3.2.1.20) produced by Xanthomonas campestris WU-9701. One of the unique properties of XgtA is that it shows extremely high α-glucosylation activity toward alcoholic and phenolic -OH groups in compounds using maltose as an α-glucosyl donor and allows for the synthesis of various useful α-glucosides with high yields. XgtA shows no hydrolytic activity toward sucrose and no α-glucosylation activity toward saccharides to produce oligosaccharides. In this report, the crystal structure of XgtA was solved at 1.72 Å resolution. The crystal belonged to space group P222, with unit-cell parameters a = 73.07, b = 83.48, and c = 180.79 Å. The β→α loop 4 of XgtA, which is proximal to the catalytic center, formed a unique structure that is not observed in XgtA homologs. Furthermore, XgtA was found to contain unique amino acid residues around its catalytic center. The unique structure of XgtA provides an insight into the mechanism for the regulation of substrate specificity in this enzyme.
α-葡萄糖基转移酶XgtA是野油菜黄单胞菌WU-9701产生的一种新型α-葡萄糖苷酶（EC 3.2.1.20）。XgtA的独特特性之一是，以麦芽糖作为α-葡萄糖基供体时，它对化合物中的醇羟基和酚羟基表现出极高的α-糖基化活性，能够高产率地合成各种有用的α-糖苷。XgtA对蔗糖没有水解活性，对糖类也没有α-糖基化活性以产生寡糖。在本报告中，XgtA的晶体结构在1.72 Å分辨率下解析完成。该晶体属于空间群P222，晶胞参数a = 73.07、b = 83.48和c = 180.79 Å。XgtA靠近催化中心的β→α环4形成了一种在XgtA同源物中未观察到的独特结构。此外，发现XgtA在其催化中心周围含有独特的氨基酸残基。XgtA的独特结构为深入了解该酶底物特异性的调控机制提供了线索。
