Enzymatic synthesis of novel branched sugar alcohols mediated by the transglycosylation reaction of pullulan-hydrolyzing amylase II (TVA II) cloned from Thermoactinomyces vulgaris R-47

Transglycosylation reactions are useful for preserving a specific sugar structure during the synthesis of branched oligosaccharides. We have previously reported a panosyl unit transglycosylation reaction by pullulan-hydrolyzing amylase II (TVA II) cloned from Thermoactinomyces vulgaris R-47 (Tonozuka et al., Carbohydr. Res., 1994, 261, 157-162). The acceptor specificity of the TVA II transglycosylation reaction was investigated using pullulan as the donor and sugar alcohols as the acceptor. TVA II transferred the α-panosyl unit to the C-1 hydroxyl group of meso-erythritol, C-1 and C-2 of xylitol, and C-1 and C-6 of d-sorbitol. TVA II differentiated between the sugar alcohols' hydroxyl groups to produce five novel non-reducing branched oligosaccharides, 1-O-α-panosylerythritol, 1-O-α-panosylxylitol, 2-O-α-panosylxylitol, 1-O-α-panosylsorbitol, and 6-O-α-panosylsorbitol. The Trp356→Ala mutant showed similar transglycosylation reactions; however, panose production by the mutant was 4.0-4.5-fold higher than that of the wild type. This suggests that Trp356 is important for recognizing both water and the acceptor molecules in the transglycosylation and the hydrolysis reaction.