The alpha-glucosyl transfer enzyme XgtA is a novel type alpha-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 aglucosylation activity toward alcoholic and phenolic -OH groups in compounds using maltose as an aglucosyl donor and allows for the synthesis of various useful alpha-glucosides with high yields. XgtA shows no hydrolytic activity toward sucrose and no alpha-glucosylation activity toward saccharides to produce oligosaccharides. In this report, the crystal structure of XgtA was solved at 1.72 angstrom resolution. The crystal belonged to space group P22(1)2(1), with unit-cell parameters a = 73.07, b = 83.48, and c = 180.79 angstrom. The (beta ->alpha 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. (C) 2020 Elsevier Inc. All rights reserved.