Biochemical characterization of glycoside hydrolase family 31 a-glucosidases from Myceliophthora thermophila for a-glucooligosaccharide synthesis

The transglucosidase activity of GH31 a-glucosidases is employed to catalyze the synthesis of prebiotic isomaltooligosaccharides (IMOs) using the malt syrup prepared from starch as substrate. Continuous mining for new GH31 a-glucosidases with high stability and efficient transglucosidase activity is critical for enhancing the supply and quality of IMO preparations. In the present study, two a-glucosidases (MT31a1 and MT31a2) from Myceliophthora thermophila were explored for biochemical characterization. The optimum pH and temperature of MT31a1 and MT31a2 were determined to be pH 4.5 and 65 degrees C, and pH 6.5 and 60 degrees C, respectively. Both MT31a1 and MT31a2 were shown to be stable in the pH range of 3.0 to 10.0. MT31a1 displayed a high thermostability, retaining 60 % of activity after incubation for 24 h at 55 degrees C. MT31a1 is highly active on substrates with all types of a-glucosidic linkages. In contrast, MT31a2 showed preference for substrates with a-(1?3) and a-(1?4) linkages. Importantly, MT31a1 was able to synthesize IMOs and the conversion rate of maltose into the main functional IMOs components reached over 40 %. Moreover, MT31a2 synthesizes glucooligosaccharides with (consecutive) a-(1?3) linkages. Taken together, MT31a1 and MT31a2, showing distinct substrate and product specificity, hold clear potential for the synthesis of prebiotic glucooligosaccharides.