초록
<P><B>Background</B></P><P>Glucoamylase is an exo-type enzyme that converts starch completely into glucose from the non-reducing ends. To meet the industrial requirements for starch processing, a glucoamylase with excellent thermostability, raw-starch degradation ability and high glucose yield is much needed. In the present study we selected the excellent Carbohydrate-Activity Enzyme (CAZyme) producer, <I>Bispora</I> sp. MEY-1, as the microbial source for glucoamylase gene exploitation.</P><P><B>Methodology/Principal Findings</B></P><P>A glucoamylase gene (<I>gla15</I>) was cloned from <I>Bispora</I> sp. MEY-1 and successfully expressed in <I>Pichia pastoris</I> with a high yield of 34.1 U/ml. Deduced GLA15 exhibits the highest identity of 64.2% to the glucoamylase from <I>Talaromyces</I> (<I>Rasamsonia</I>) <I>emersonii</I>. Purified recombinant GLA15 was thermophilic and showed the maximum activity at 70°C. The enzyme was stable over a broad pH range (2.2–11.0) and at high temperature up to 70°C. It hydrolyzed the breakages of both α-1,4- and α-1,6-glycosidic linkages in amylopectin, soluble starch, amylose, and maltooligosaccharides, and had capacity to degrade raw starch. TLC and H<SUP>1</SUP>-NMR analysis showed that GLA15 is a typical glucoamylase of GH family 15 that releases glucose units from the non-reducing ends of α-glucans. The combination of <I>Bacillus licheniformis</I> amylase and GLA15 hydrolyzed 96.14% of gelatinized maize starch after 6 h incubation, which was about 9% higher than that of the combination with a commercial glucoamylase from <I>Aspergillus niger</I>.</P><P><B>Conclusion/Significance</B></P><P>GLA15 has a broad pH stability range, high-temperature thermostability, high starch hydrolysis capacity and high expression yield. In comparison with the commercial glucoamylase from <I>A. niger</I>, GLA15 represents a better candidate for application in the food industry including production of glucose, glucose syrups, and high-fructose corn syrups.</P>