Characterization of cyclodextrin glycosyltransferases (CGTases) and their application for synthesis of alkyl glycosides with oligomeric head group

• Four CGTases were shown to have widely different catalytic properties.
• Carbohydrate elongation of alkyl glycosides was achieved with all CGTases.
• Paenibacillus macerans CGTase was outstanding for coupling reactions.
• Most CGTases produced a broad product distribution.
• Carboxydocella sp. CGTase produced highly elongated products.

Cyclodextrin glycosyltransferases (CGTases) from Paenibacillus macerans, Thermoanaerobacter sp. ATCC 53627, Bacillus stearothermophilus and a Carboxydocella sp. (phylogenetically identified from genomic DNA) were characterized with respect to their catalytic activity in different reactions, with emphasis on reactions useful for the elongation of the carbohydrate group of alkyl glycosides. All CGTases had activities between 95 and 115 U/mg in the coupling reaction between α-cyclodextrin (α-CD) as glucosyl donor and β-dodecyl maltoside as glucosyl acceptor, but differed very much in the competing hydrolysis of α-CD. The α-CD hydrolysis activity ranged from 0.13 U/mg for P. macerans CGTase to 10.5 U/mg for the Carboxydocella sp. (CspCGT13). Furthermore, the disproportionation activity was much lower for the Paenibacillus CGTase compared to the other CGTases, and consequently this enzyme produced the highest yield of the primary coupling product β-dodecyl maltooctaoside, which is a valuable surfactant. For production of a polydisperse alkyl glycoside product, disproportionation reactions are useful and the other three CGTases of the current study are efficient catalysts. The newly discovered Carboxydocella sp. (CspCGT13) CGTase has the special feature to produce more of products with even longer carbohydrate groups than the primary coupling product.

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