Abstract
An Aspergillus oryzae RIB40 (NBRC100959) α-glucosidase （designed as AgdB）gene (agdB) was expressed at high levels in an A. oryzae host by self-cloning. The obtained transformant (MIBA1002) produced intracellular and extracellular α-glucosidase at levels 3- and 10-fold higher, respectively, than the parent host strain. The base sequence of agdB consisted of a 3036-kb structural gene containing three introns and encoding 963 amino acids, and the linear sequence thus obtained from these amino acids was identical to A. oryzae RIB40 unknown protein BAE64257.1. The amino acid sequence had 72% and 51% homology to α-glucosidase B from Aspernillus nidulans and Acremonium implicatum, respectively, which exhibit transglycosylation activity. The sequence has conserved residues specific to glucosyl hydrase family 31 (GH31) α-glucosidases. Tyr296 present in the β→α Loop1 in GH31 is important for transglycosylation. The enzyme produced 2.2% isomaltose, 0.4% maltotriose, and 0.3%
kojibiose from 20% maltose substrate. This is the first report of the transglycosylation activity
of α-glucosidase B cloned in A. oryzae (unknown protein BAE64257.1).
