title: Cloning, expression, characterization, and nucleophile identification of family 3, Aspergillus niger beta-glucosidase.
abstract: The beta-glucosidase from Aspergillus niger (CMI CC 324262) was purified, and an N-terminal sequence and two internal sequences were determined. BglI genomic gene and the cDNA were cloned from a genomic library and by reverse transcriptase-polymerase chain reaction, respectively. The cDNA was successfully expressed in Saccharomyces cerevisiae and Pichia pastoris. Sequence analysis revealed that the gene encodes a 92-kDa enzyme that is a member of glycosidase family 3. (1)H-NMR analysis of the reaction catalyzed by this enzyme confirmed that, in common with other family 3 glycosidases, this enzyme hydrolyzes with net retention of anomeric configuration. Accordingly, the enzyme was inactivated by 2-deoxy-2-fluoro beta-glucosyl fluoride, with kinetic parameters of k(i) = 4.5 min(-1), K(I) = 35.4 mM, through the trapping of a covalent glycosyl enzyme intermediate. The catalytic competence of this intermediate was demonstrated by the fact that incubation with linamarin resulted in reactivation, presumably via a transglycosylation mechanism. Peptic digestion of the 2-deoxy-2-fluoroglucosyl enzyme and subsequent analysis of high pressure liquid chromatography eluates by electrospray ionization triple quadrupole mass spectrometry in the neutral loss mode allowed the localization of a 2-deoxy-2-fluoroglucosyl-peptide. Sequence determination of this labeled peptide by tandem mass spectrometry in the daughter ion scan mode permitted the identification of Asp-261 as the catalytic nucleophile within the sequence VMSDW. Asp-261 is fully conserved within this family, consistent with its key role, and aligns with the aspartic acid residue previously identified in the Aspergillus wentii enzyme by labeling with conduritol B epoxide (Bause, E., and Legler, G. (1974) Hoppe-Seyler's Z. Physiol. Chem. 355, 438-442).
authors.affiliation: The Kennedy Leigh Centre for Horticultural Research and The Otto Warburg Center for Agricultural Biotechnology, The Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel.
authors.forename: S
authors.initials: S
authors.lastname: Dan
authors.forename: I
authors.initials: I
authors.lastname: Marton
authors.forename: M
authors.initials: M
authors.lastname: Dekel
authors.forename: B A
authors.initials: BA
authors.lastname: Bravdo
authors.forename: S
authors.initials: S
authors.lastname: He
authors.forename: S G
authors.initials: SG
authors.lastname: Withers
authors.forename: O
authors.initials: O
authors.lastname: Shoseyov
mesh_terms: D000595:Amino Acid Sequence; D001234:Aspergillus niger / Q000201:enzymology*; D001483:Base Sequence; D003001:Cloning, Molecular; D004271:DNA, Fungal; D004591:Electrophoresis, Polyacrylamide Gel; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D001617:beta-Glucosidase / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D004271:DNA, Fungal; D001617:beta-Glucosidase