Purification, characterization and gene analysis of a new α-glucosidase from shiraia sp. SUPER-H168

A new α-glucosidase from Shiraia sp. SUPER-H168 under solid-state fermentation was purified by alcohol precipitation and anion-exchange and by gel filtration chromatography. The optimum pH and temperature of the purified α-glucosidase were 4.5 and 60 °C, respectively, using p -nitrophenyl-α-glucopyranoside (α- p NPG) as a substrate. Ten millimoles of sodium dodecyl sulfate, Fe 2+ , Cu 2+ , and Ag + reduced the enzyme activity to 0.7, 7.6, 26.0, and 6.2 %, respectively, of that of the untreated enzyme. The K m , V max , and k cat / K m of the α-glucosidase were 0.52 mM, 3.76 U mg −1 , and 1.3 × 10 4 L s −1 mol −1 , respectively. K m with maltose was 0.62 mM. Transglycosylation activities were observed with maltose and sucrose as substrates, while there was no transglycosylation with trehalose. DNA and its corresponding full-length cDNA were cloned and analyzed. The α-glucosidase coding region consisted of a 2997-bp open reading frame encoding a 998-amino acid protein with a 22-amino acid signal peptide; one 48-bp intron was located. The α-glucosidase was a monomeric protein with a predicted molecular mass of 108.2 kDa and a predicted isoelectric point of 5.08. A neighbor-joining phylogenetic tree demonstrated that Shiraia sp. SUPER-H168 α-glucosidase is an ascomycetes α-glucosidase. This is the first report of α-glucosidase from a filamentous fungus that had good glycoside hydrolysis with maltose and α- p NPG, transglycosylation and conversion activity of maltose into trehalose.