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|Title:||Substrate binding and catalytic mechanism of a barley b-D-glucosidase (1,4)-b-D-glucan exohydrolase|
|Citation:||Journal of Biological Chemistry, 1998; 273(18):11134-11143|
|Publisher:||AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC|
|Abstract:||A beta-glucosidase, designated isoenzyme betaII, from germinated barley (Hordeum vulgare L.) hydrolyzes aryl-beta-glucosides and shares a high level of amino acid sequence similarity with beta-glucosidases of diverse origin. It releases glucose from the non-reducing termini of cellodextrins with catalytic efficiency factors, kcat/Km, that increase approximately 9-fold as the degree of polymerization of these substrates increases from 2 to 6. Thus, the enzyme has a specificity and action pattern characteristic of both beta-glucosidases (EC 184.108.40.206) and the polysaccharide exohydrolase, (1,4)-beta-glucan glucohydrolase (EC 220.127.116.11). At high concentrations (100 mM) of 4-nitrophenyl beta-glucoside, beta-glucosidase isoenzyme betaII catalyzes glycosyl transfer reactions, which generate 4-nitrophenyl-beta-laminaribioside, -cellobioside, and -gentiobioside. Subsite mapping with cellooligosaccharides indicates that the barley beta-glucosidase isoenzyme betaII has six substrate-binding subsites, each of which binds an individual beta-glucosyl residue. Amino acid residues Glu181 and Glu391 are identified as the probable catalytic acid and catalytic nucleophile, respectively. The enzyme is a family 1 glycoside hydrolase that is likely to adopt a (beta/alpha)8 barrel fold and in which the catalytic amino acid residues appear to be located at the bottom of a funnel-shaped pocket in the enzyme.|
|Keywords:||Hordeum; beta-Glucosidase; Glucan 1,4-beta-Glucosidase; Peptide Mapping; Crystallography, X-Ray; Amino Acid Sequence; Substrate Specificity; Kinetics; Catalysis; Models, Chemical; Molecular Sequence Data|
|Appears in Collections:||Agriculture, Food and Wine publications|
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