Amino acids in conserved region II are crucial to substrate specificity, reaction velocity, and regioselectivity in the transglucosylation of honeybee GH-13 α-glucosidases.

Honeybees, Apis mellifera, possess three α-glucosidase isozymes, HBG-I, HBG-II, and HBG-III, which belong to glycoside hydrolase family 13. They show high sequence similarity, but clearly different enzymatic properties. HBG-III preferred sucrose to maltose as substrate and formed only α-1,4-glucosidic linkages by transglucosylation, while HBG-II preferred maltose and formed the α-1,6-linkage.

Molecular cloning of cDNAs and genes for three alpha-glucosidases from European honeybees, Apis mellifera L., and heterologous production of recombinant enzymes in Pichia pastoris.

cDNAs encoding three alpha-glucosidases (HBGases I, II, and III) from European honeybees, Apis mellifera, were cloned and sequenced, two of which were expressed in Pichia pastoris. The cDNAs for HBGases I, II, and III were 1,986, 1,910, and 1,915 bp in length, and included ORFs of 1,767, 1,743, and 1,704 bp encoding polypeptides comprised of 588, 580, and 567 amino acid residues, respectively. The deduced proteins of HBGases I, II, and III contained 18, 14, and 8 putative N-linked glycosylation sites, respectively, but at least 2 sites in HBGase II were unmodified by N-linked oligosaccharide.