Enzymatic Synthesis of Polyol- and Masked Polyol- Glycosides using β-Glycosidase ofSulfolobus Solfataricus

Enzymatic glycosylation of small molecules: challenging substrates require tailored catalysts

Glycosylation can significantly improve the physicochemical and biological properties of small molecules like vitamins, antibiotics, flavors, and fragrances. The chemical synthesis of glycosides is, however, far from trivial and involves multistep routes that generate lots of waste. In this review, biocatalytic alternatives are presented that offer both stricter specificities and higher yields. The advantages and disadvantages of different enzyme classes are discussed and illustrated with a number of recent examples. Progress in the field of enzyme engineering and screening are expected to result in new applications of biocatalytic glycosylation reactions in various industrial sectors.

Developing Promiscuous Glycosidases for Glycoside Synthesis: Residues W433 and E432 in Sulfolobus solfataricus β-Glycosidase are Important Glucoside- and Galactoside-Specificity Determinants

Two residues that have been implicated in determining the substrate specificity of the thermophilic beta-glycosidase from the archaeon Sulfolobus solfataricus (SsbetaG), a member of the glycosyl hydrolase family 1, have been mutated by site-directed mutagenesis so as to create more versatile catalysts for carbohydrate chemistry. The wild-type and mutated sequences were expressed in E. coli with a His(7)-tag to allow one-step chromatographic purification. The E432C and W433C mutations removed key interactions with the OH-4 and OH-3 of the sugar substrates, thus reducing the discrimination of glucose, galactose and fucose with respect to other glycosides. This resulted in two glycosidases with greatly broadened substrate specificities. Observed changes include a 24-fold increase in Man:Gal activity and an 18-fold increase in GalA:Gal activity. This promiscuous substrate tolerance was further illustrated by the parallel synthesis of a beta-glycoside library of glucose, galactose, xylose and mannose in one pot at 50 degrees C, in organic solvent. The synthetic potential of the catalysts was further evaluated through alkyl glycoside transglycosylation yields, including the first examples of synthesis of beta-mannosides and beta-xylosides with SsbetaG.

A novel thermophilic glycosynthase that effects branching glycosylation

A novel thermophilic glycosynthase that effects branching glycosylation has been obtained by mutation of the nucleophile in the active site of the glycosidase from Sulfolobus solfataricus. Two methods for the use of this mutant are reported.

Glycosidases and glycosyl transferases in glycoside and oligosaccharide synthesis

Remarakable advances in glycobiology in recent years have stimulated a resurgence of interest in carbohydrate chemistry. The challenge of producing the complex glycosides and oligosaccharides needed for research in glycobiology has led to the development of enzymatic methods that are now firmly established as part of the synthetic repertoire of the carbohydrate chemist.