Identification of a novel type I pullulanase from Fervidobacterium nodosum Rt17-B1, with high thermostability and suitable optimal pH.

Pullulanase could be used in many industrial processes due to its ability to hydrolyze α-1,6-glucosidic linkage. During the use of high temperature conditions in industrial production, pullulanase requires high resistance of heat. In this study, a novel type I pullulanase from Fervidobacterium nodosum Rt17-B1 (FN-pullulanase) with a suitable optimal pH and thermostability was discovered. Sequence analysis of FN-pullulanase showed that the enzyme had the typical motif of type I pullulanase (YNWGYDP). The recombinant FN-pullulanase, expressed in Escherichia coli, was purified as a single band on SDS-PAGE with a molecular mass of about 95 kDa. The enzyme showed optimum activity at pH 5.0 and 80 °C, and its specific activity was 25.93 U/mg. FN-pullulanase also exhibited good pH stability and thermostability. More than 80% of its initial activity was retained after incubated on ice at pH 3.5-9.0 for 24 h. Its half-life at 65 °C was 115.5 h. The enzyme could completely convert pullulan to maltotriose, as well as hydrolyze soluble starch or amylopectin to maltose, maltotriose, maltotetraose, maltopentaose and maltohexaose (G2-G6). Generally, this study identified a novel FN-pullulanase with both high thermostability and suitable optimum pH, which had the potential to be used in starch conversion process.