title: Aspergillus nidulans alpha-galactosidase of glycoside hydrolase family 36 catalyses the formation of alpha-galacto-oligosaccharides by transglycosylation.
abstract: The alpha-galactosidase from Aspergillus nidulans (AglC) belongs to a phylogenetic cluster containing eukaryotic alpha-galactosidases and alpha-galacto-oligosaccharide synthases of glycoside hydrolase family 36 (GH36). The recombinant AglC, produced in high yield (0.65 g.L(-1) culture) as His-tag fusion in Escherichia coli, catalysed efficient transglycosylation with alpha-(1-->6) regioselectivity from 40 mm 4-nitrophenol alpha-d-galactopyranoside, melibiose or raffinose, resulting in a 37-74% yield of 4-nitrophenol alpha-D-Galp-(1-->6)-D-Galp, alpha-D-Galp-(1-->6)-alpha-D-Galp-(1-->6)-D-Glcp and alpha-D-Galp-(1-->6)-alpha-D-Galp-(1-->6)-D-Glcp-(alpha1-->beta2)-d-Fruf (stachyose), respectively. Furthermore, among 10 monosaccharide acceptor candidates (400 mm) and the donor 4-nitrophenol alpha-D-galactopyranoside (40 mm), alpha-(1-->6) linked galactodisaccharides were also obtained with galactose, glucose and mannose in high yields of 39-58%. AglC did not transglycosylate monosaccharides without the 6-hydroxymethyl group, i.e. xylose, L-arabinose, L-fucose and L-rhamnose, or with axial 3-OH, i.e. gulose, allose, altrose and L-rhamnose. Structural modelling using Thermotoga maritima GH36 alpha-galactosidase as the template and superimposition of melibiose from the complex with human GH27 alpha-galactosidase supported that recognition at subsite +1 in AglC presumably requires a hydrogen bond between 3-OH and Trp358 and a hydrophobic environment around the C-6 hydroxymethyl group. In addition, successful transglycosylation of eight of 10 disaccharides (400 mm), except xylobiose and arabinobiose, indicated broad specificity for interaction with the +2 subsite. AglC thus transferred alpha-galactosyl to 6-OH of the terminal residue in the alpha-linked melibiose, maltose, trehalose, sucrose and turanose in 6-46% yield and the beta-linked lactose, lactulose and cellobiose in 28-38% yield. The product structures were identified using NMR and ESI-MS and five of the 13 identified products were novel, i.e. alpha-D-Galp-(1-->6)-D-Manp; alpha-D-Galp-(1-->6)-beta-D-Glcp-(1-->4)-D-Glcp; alpha-D-Galp-(1-->6)-beta-D-Galp-(1-->4)-D-Fruf; alpha-D-Galp-(1-->6)-D-Glcp-(alpha1-->alpha1)-D-Glcp; and alpha-D-Galp-(1-->6)-alpha-D-Glcp-(1-->3)-D-Fruf.
authors.affiliation: Enzyme and Protein Chemistry, Department of Systems Biology, Technical University of Denmark, Lyngby, Denmark.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakai
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Baumann
authors.forename: Bent O
authors.initials: BO
authors.lastname: Petersen
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Westphal
authors.forename: Maher Abou
authors.initials: MA
authors.lastname: Hachem
authors.forename: Adiphol
authors.initials: A
authors.lastname: Dilokpimol
authors.forename: Jens Ø
authors.initials: JØ
authors.lastname: Duus
authors.forename: Henk A
authors.initials: HA
authors.lastname: Schols
authors.forename: Birte
authors.initials: B
authors.lastname: Svensson
mesh_terms: D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000201:enzymology*; D055162:Biocatalysis; D002236:Carbohydrate Conformation; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000378:metabolism; D006031:Glycosylation; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008958:Models, Molecular; D009844:Oligosaccharides / Q000096:biosynthesis* / Q000737:chemistry; D010802:Phylogeny; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D013696:Temperature; D000519:alpha-Galactosidase / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D009844:Oligosaccharides; D011994:Recombinant Proteins; D000519:alpha-Galactosidase