Tailoring pullulanase PulAR from Anoxybacillus sp. AR-29 for enhanced catalytic performance by a structure-guided consensus approach.

Pullulanase is a well-known debranching enzyme that can specifically hydrolyze α-1,6-glycosidic linkages in starch and oligosaccharides, however, it suffers from low stability and catalytic efficiency under industrial conditions. In the present study, four residues (A365, V401, H499, and T504) lining the catalytic pocket of Anoxybacillus sp. AR-29 pullulanase (PulAR) were selected for site-directed mutagenesis (SDM) by using a structure-guided consensus approach. Five beneficial mutants (PulAR-A365V, PulAR-V401C, PulAR-A365/V401C, PulAR-A365V/V401C/T504V, and PulAR-A365V/V401C/T504V/H499A) were created, which showed enhanced thermostability, pH stability, and catalytic efficiency. Among them, the quadruple mutant PulAR-A365V/V401C/T504V/H499A displayed 6.6- and 9.6-fold higher catalytic efficiency toward pullulan at 60 ℃, pH 6.0 and 5.0, respectively. In addition, its thermostabilities at 60 ℃ and 65 ℃ were improved by 2.6- and 3.1-fold, respectively, compared to those of the wild-type (WT). Meanwhile, its pH stabilities at pH 4.5 and 5.0 were 1.6- and 1.8-fold higher than those of WT, respectively. In summary, the catalytic performance of PulAR was significantly enhanced by a structure-guided consensus approach. The resultant quadruple mutant PulAR-A365V/V401C/T504V/H499A demonstrated potential applications in the starch industry.