title: The E358S mutant of Agrobacterium sp. beta-glucosidase is a greatly improved glycosynthase.
abstract: Glycosynthases are nucleophile mutants of retaining glycosidases that catalyze the glycosylation of sugar acceptors using glycosyl fluoride donors, thereby synthesizing oligosaccharides. The 'original' glycosynthase, derived from Agrobacterium sp. beta-glucosidase (Abg) by mutating the nucleophile glutamate to alanine (E358A), synthesizes oligosaccharides in yields exceeding 90% [Mackenzie, L.F., Wang, Q., Warren, R.A.J. and Withers, S.G. (1998) J. Am. Chem. Soc. 120, 5583-5584]. This mutant has now been re-cloned with a His(6)-tag into a pET-29b(+) vector, allowing gram scale production and single step chromatographic purification. A dramatic, 24-fold, improvement in synthetic rates has also been achieved by substituting the nucleophile with serine, resulting in improved product yields, reduced reaction times and an enhanced synthetic repertoire. Thus poor acceptors for Abg E358A, such as PNP-GlcNAc, are successfully glycosylated by E358S, allowing the synthesis of PNP-beta-LacNAc. The increased glycosylation activity of Abg E358S likely originates from a stabilizing interaction between the Ser hydroxyl group and the departing anomeric fluorine of the alpha-glycosyl fluoride.
authors.affiliation: Protein Engineering Network of Centres of Excellence, Department of Chemistry, University of British Columbia, Vancouver, B.C., Canada.
authors.forename: C
authors.initials: C
authors.lastname: Mayer
authors.forename: D L
authors.initials: DL
authors.lastname: Zechel
authors.forename: S P
authors.initials: SP
authors.lastname: Reid
authors.forename: R A
authors.initials: RA
authors.lastname: Warren
authors.forename: S G
authors.initials: SG
authors.lastname: Withers
mesh_terms: D019943:Amino Acid Substitution; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D006031:Glycosylation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D017354:Point Mutation; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012231:Rhizobium / Q000201:enzymology* / Q000235:genetics*; D013379:Substrate Specificity; D001617:beta-Glucosidase / Q000235:genetics* / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D009844:Oligosaccharides; D011994:Recombinant Proteins; D001617:beta-Glucosidase