Study on Three .ALPHA.-Glucosidase Isozymes from Honeybee, Apis mellifera L.

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  • Nishimoto Mamoru
    Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University
  • Mori Haruhide
    Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University
  • Kimura Atsuo
    Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University
  • Chiba Seiya
    Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University

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Other Title
  • 3種のミツバチα-グルコシダーゼアイソザイムの構造と機能
  • 3シュ ノ ミツバチ アルファ グルコシダーゼアイソザイム ノ コウゾウ ト キノウ

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Abstract

The genes of three a-glucosidases (HBG I, HBG II and HBG III) were isolated from the cDNA library of honeybee, Apis mellifera L. The nucleotide sequences of HBG I, II and III were consisted of 1974, 1910 and 1916 base pair and encoding 588, 580 and 567 amino acid residues, respectively. The putative primary structures showed high homology ranging from N- to C-terminals, and three enzymes belonged to a-glucosidase family I, in which four conservative regions of aamylase family were observed in their sequences. To obtain the recombinant enzymes, we tried to express the cDNAs in Pichia pastoris of heterologous host cells. Although recombinant HBG I was not produced, the recombinant HBG II and III of 2.4 and 1.2 U/mg were respectively expressed and secreted into culture supernatant. The active recombinant enzymes purified had the same properties as those of native ones except sugar content. To investigate the catalytic residues in HBGs, four mutated enzymes (D206N, E259Q, E269Q and D33 1N) of HBG III were constructed, and their specific activities were found to be 0.0004, 4.9, 0.004 and 0.0002 U/mg, respectively. E259Q remained half activity of wild type and those of the others disappeared, implying that three catalyticresidues of HBGs were D212, E281 and D343 of HBG I, D202, E271 and D333 of HBG II, D206, E269 and D331 of HBG III. The homology modeling showed that three enzymes had Ndomain ((β/α)8 barrel), subdomain, and C-domain(β-sheet structure mainly) like oligo-l, 6-glucosidase from Bacillus cereus.

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