Cyclodextrin Glycosyltransferase--Catalysis of Irreversible C-F Glycosylic Bond Cleavage and de novo Maltosidic Linkage Synthesis (Dexter French教授追悼号)

概要

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New insight has been obtained into the catalytic capabilities of cyclodextrin glycosyltransferase, an enzyme long believed to attack only maltosidic linkages and to catalyze only glycosidic linkage exchange. The effective conversion of α-maltosyl fluoride to α-maltosaccharide 1-fluorides and cyclodextrins reveals the enzyme's additional ability to cleave C-F glycosylic bonds and to catalyze a class of irreversible reactions providing de novo glycosidic linkage synthesis. Cyclodextrin formation by Bacillus macerans CGTase, heretofore observed only with starch and dextrins, was more pronounced with α-maltosyl fluoride than with maltotetraose; conversion of the dimeric fluoride to α-, β-, and γ-cyclodextrins by Bacillus megaterium CGTase was as great (90%) as with the best of CGTase substrates. Although glycosidic exchange reactions occur in digests with α-maltosyl fluoride, the very effective conversion of this small molecule to higher DP products is the consequence of novel reactions of "total chain lengthening" (α-G2F+α-G2Fα-G4F+HF, etc.) and "total cyclization" (e.g., α-G7Fβ-CD +HF) not found with traditional substrates. The results establish CGTase to be a glycosyl mobilizing enzyme, and illustrate the inadequacy of the long accepted notion that glycosyltransferases require donors with a glycosidic bond.
日本応用糖質科学会の論文