A novel alpha-D-galactosynthase from Thermotoga maritima converts beta-D-galactopyranosyl azide to alpha-galacto-oligosaccharides.

The large-scale production of oligosaccharides is a daunting task, hampering the study of the role of glycans in vivo and the testing of the efficacy of novel glycan-based drugs. Glycosynthases, mutated glycosidases that synthesize oligosaccharides in high yields, are becoming important chemo-enzymatic tools for the production of oligosaccharides. However, while ²-glycosynthase can be produced with a rather well established technology, examples of ±-glycosynthases are thus far limited only to enzymes from families GH29, GH31 and GH95. ±-L-Fucosynthases from GH29 use convenient glycosyl azide derivatives as a strategic alternative to glycosyl fluoride donors. However, the general applicability of this method to other ±-glycosynthases is not trivial and remains to be confirmed. Here, ²-D-galactopyranosyl azide was converted to ±-galacto-oligosaccharides with good yields and high regioselectivity, catalyzed by a novel ±-galactosynthase based on the GH36 ±-galactosidase from the hyperthermophilic bacterium Thermotoga maritima. These results open a new avenue to the practical synthesis of biologically interesting ±-galacto-oligosaccharides and demonstrate more widespread use of ²-glycosyl-azide as donors confirming their utility to expand the repertoire of glycosynthases.