PspAG97A: A Halophilic α-Glucoside Hydrolase with Wide Substrate Specificity from Glycoside Hydrolase Family 97

A novel alpha-glucoside hydrolase (named PspAG97A) from glycoside hydrolase family 97 (GH97) was cloned from the deep-sea bacterium Pseudoalteromonas sp. K8, which was screened from the sediment of Kongsfjorden. Sequence analysis showed that PspAG97A belonged to GH97, and shared 41% sequence identity with the characterized alpha-glucosidase BtGH97a. PspAG97A possessed three key catalytically related glutamate residues. Mutation of the glutamate residues indicated that PspAG97A belonged to the inverting subfamily of GH97. PspAG97A showed significant reversibility against changes in salt concentration. It exhibited halophilic ability and improved thermostability in NaCl solution, with maximal activity at 1.0 M NaCl/KCl, and retained more than 80% activity at NaCl concentrations ranging from 0.8 to 2.0 M for over 50 h. Furthermore, PspAG97A hydrolyzed not only alpha-1,4-glucosidic linkage, but also alpha-1,6- and alpha-1,2-glucosidic linkages. Interestingly, PspAG97A possessed high catalytic efficiency for long-chain substrates with alpha-1,6-linkage. These characteristics are clearly different from other known a-glucoside hydrolases in GH97, implying that PspAG97A is a unique alpha-glucoside hydrolase of GH97.