Glycosylation of internal sugar residues of oligosaccharides catalyzed by α-galactosidase from Aspergillus fumigatus

• Published in: Biochimica et biophysica acta Vol. 1726; no. 2; pp. 206 - 216
• Main Authors: Puchart, Vladimír, Biely, Peter
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.11.2005
• Subjects: alpha-Galactosidase - chemistry; Aspergillus fumigatus; Aspergillus fumigatus - enzymology; Galactomannan; Glucosides - chemistry; Glycosylation; Internal sugar residues; Oligosaccharides - chemistry; Protein Structure, Tertiary; Transgalactosylation; α-galactosidase; NPGal; Gal 1Man 3; Gal 1Man 2; Galactomannan; Transgalactosylation; α-galactosidase; Gal 2Man 2; Internal sugar residues; Galα6Man; Man 2 through Man 6; Aspergillus fumigatus
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2005.07.015

Purified α-galactosidase from a thermotolerant fungus Aspergillus fumigatus IMI 385708 was found to catalyze efficiently transgalactosylation reactions using 4-nitrophenyl α- 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 α-1,4-gluco- (maltooligosaccharides), β-1,4-gluco- (cellooligosaccharides) and β-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 β-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.