Alpha-L-fucosidases: exoglycosidases with unusual transglycosylation properties.

Apha-LFucosidases (EC 3.2.1.51), the only members of the CAZy family GH-29, are widespread glycosidases involved in many biological processes including inflammation, metastasis, and the lysosomal storage disease fucosidosis. Despite their biological significance, information concerning the mechanism of alpha-Lfucosidases has only recently become available. In an attempt to obtain further data concerning their mechanism, we have investigated the hydrolytic and transglycosylation properties of a canine and a mollusk (Pecten maximus) alpha-Lfucosidase. Our results show that, despite the evolutionary distance between these two species, both enzymes have similar hydrolysis and transglycosylation properties. Surprisingly, we found that, starting from monosaccharides, these exoglycosidases were able to catalyze efficiently the synthesis of highly branched fuco-oligosaccharides as large as tetrasaccharides, a unique feature for a wild-type exoglycosidase. The structural analysis of the compounds formed revealed that the regioselectivity of alpha-Lfucosidases is strongly influenced by the structure of the acceptor. This leads us to propose an enzymatic approach for the preparative synthesis of fuco-oligosaccharides. This will not only allow the synthesis of biological determinants containing fucose but also of new fucose-containing oligosaccharides as alpha-glycosynthases appear to be difficult to obtain.