Glycosylation of internal sugar residues of oligosaccharides catalyzed by alpha-galactosidase from Aspergillus fumigatus.
Purified alpha-galactosidase from a thermotolerant fungus Aspergillus fumigatus IMI 385708 was found to catalyze efficiently transgalactosylation reactions using 4-nitrophenyl alpha-D-galactopyranoside as glycosyl donor. Self-transfer reactions with this substrate afforded in low yields several 4-nitrophenyl galactobiosides. Monosaccharides also served as poor glycosyl acceptors. Disaccharides and particularly higher oligosaccharides of alpha-1,4-gluco- (maltooligosaccharides), beta-1,4-gluco- (cellooligosaccharides) and beta-1,4-manno-series were efficiently galactosylated, the latter being the best acceptors that were also doubly galactosylated. With mannooligosaccharides product yields increased with polymerization degree of acceptors reaching 50% at DP of 4-6. Longer oligosaccharide acceptors were galactosylated at internal sugar residues. All galactosyl residues were transferred exclusively to the primary hydroxyl group(s) at C-6 position of oligosaccharide acceptors. This is in accordance with the inability of the enzyme to transfer galactose to beta-1,4-linked xylooligosaccharides. This is the first report of glycosyl transfer reaction to internal sugar residues of oligosaccharides catalyzed by a glycosidase. High affinity to oligosaccharide acceptors also opens a way toward enzymatic glycosylation of polysaccharides, thus modulating their physico-chemical and biological properties.
Puchart
Vladimír
V
Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 38 Bratislava 45, Slovak Republic.
Biely
Peter
P
D001232:Aspergillus fumigatus / Q000201:enzymology*; D005960:Glucosides / Q000737:chemistry*; D006031:Glycosylation; D009844:Oligosaccharides / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D000519:alpha-Galactosidase / Q000737:chemistry*
D005960:Glucosides; D009844:Oligosaccharides; C021705:maltooligosaccharides; C019502:4-nitrophenyl alpha-glucoside; D000519:alpha-Galactosidase