Isomaltulose Synthase from Klebsiella sp. Strain LX3: Gene Cloning and Characterization and Engineering of Thermostability

AUTOR(ES)

Zhang, Daohai

FONTE

American Society for Microbiology

RESUMO

The gene (palI) encoding isomaltulose synthase (PalI) from a soil bacterial isolate, Klebsiella sp. strain LX3, was cloned and characterized. PalI converts sucrose into isomaltulose, trehalulose, and trace amounts of glucose and fructose. Sequence domain analysis showed that PalI contains an α-amylase domain and (β/α)8-barrel structures, suggesting that it belongs to the α-amylase family. Sequence alignment indicated that the five amino acid residues of catalytic importance in α-amylases and glucosyltransferases (Asp241, Glu295, Asp369, His145, and His368) are conserved in PalI. Purified recombinant PalI displayed high catalytic efficiency, with a Km of 54.6 ± 1.7 mM for sucrose, and maximum activity (approximately 328.0 ± 2.5 U/mg) at pH 6.0 and 35°C. PalI activity was strongly inhibited by Fe3+ and Hg2+ and was enhanced by Mn2+ and Mg2+. The half-life of PalI was 1.8 min at 50°C. Replacement of selected amino acid residues by proline significantly increased the thermostability of PalI. Simultaneous replacement of Glu498 and Arg310 with proline resulted in an 11-fold increase in the half-life of PalI at 50°C.

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