Characterizing a thermostable amylopullulanase from Caldisericum exile with wide pH adaptation and broad substrate specificity

Abstract To improve starch processing as well as enrich the enzyme resources, an amylopullulanase (CEApu) from Caldisericum exile was heterologously expressed and characterized. CEApu was identified as a glycoside hydrolase from glycoside hydrolase (GH) family 57. The optimal temperature and optimal pH were determined to be 75°C, and pH 5.5 and 8.5, respectively. CEApu had a wide pH adaptation and activity, retaining >50% activity from pH 4.5–10.0. CEApu also had broad substrate specificity, as it could hydrolyze α-1,4/α-1,6 glycosidic linkages in starch, dextrin, oligosaccharide (degree of polymerization (DP) >3), pullulan, and even γ-cyclodextrin (γ-CD), but not α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD). The maximum reducing sugar content was 103 mg/g released from gelatinized cassava starch. CEApu was a biocatalyst that may be used for the preparation of starch sugars, resistant starches or linear dextrins. These results confirmed that CEApu was a thermostable amylopullulanase with a strong application potential.