Non-ionic surfactants such as alkyl glycosides have a wide range of applications which made them an interesting target for biotechnological industries. It has been shown that elongation of the hydrophilic group makes them milder to cells and tissues, which make elongation of the carbohydrate part of alkylglycosides of particular interest. The elongation process of an alkyl glycoside can be achieved very efficiently by using α-cyclodextrin as donor in coupling reactions catalyzed by CGTase . Cyclodextrin glucanotransferases (CGTases) (EC 18.104.22.168) belongs to GH family 13 and are also capable of catalysing cyclization, hydrolysis and disproportionation by using substrates like starch. This opens up the possibility to synthesize a whole range of highly interesting surfactants with elongated carbohydrate groups.
Recently we have characterized a novel CGTase (CspCGT13) from Carboxydocella, which was used to elongate dodecyl-β-maltoside (β-DDM) . The enzyme displayed high coupling activity using γ-CD as donor and β-DDM as acceptor. CspCGT13 was also efficient in elongating β-DDM by using α-CD . However, in both cases the disproportionation reaction was dominating over the coupling reaction which limits the usability of this enzyme for producing well-defined alkyl glycosides (table 1 & 2). On the other hand the high disproportionation reactivity of CspCGT13 makes it an interesting candidate for synthesizing alkyl polyglycosides (APGs). We have also used site-directed mutagenesis approach to improve the coupling activity and the primary results shows improved coupling/disproportionation ratio.
This project was supported by FORMAS (Grant 2015-769).
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