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References
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[1]
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Resource
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Comments
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Medline ID
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PubMed ID
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8617814
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Journal
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J Biol Chem
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Year
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1996
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Volume
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271
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Pages
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5277-86
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Authors
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Hrmova M, Harvey AJ, Wang J, Shirley NJ, Jones GP, Stone BA, Hoj PB, Fincher GB
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Title
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Barley beta-D-glucan exohydrolases with beta-D-glucosidase activity. Purification, characterization, and determination of primary structure from a cDNA clone.
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Related PDB
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Related UniProtKB
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[2]
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Resource
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Comments
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Medline ID
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PubMed ID
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Journal
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Carbohydr Res
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Year
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1998
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Volume
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305
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Pages
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209-21
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Authors
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Hrmova M, Fincher GB
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Title
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Barley beta-D-glucan exohydrolases. Substrate specificity and kinetic properties.
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Related PDB
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Related UniProtKB
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[3]
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Resource
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Comments
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X-RAY CRYSTALLOGRAPHY (2.2 ANGSTROMS) OF 26-630.
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Medline ID
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PubMed ID
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10368285
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Journal
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Structure Fold Des
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Year
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1999
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Volume
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7
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Pages
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179-90
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Authors
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Varghese JN, Hrmova M, Fincher GB
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Title
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Three-dimensional structure of a barley beta-D-glucan exohydrolase, a family 3 glycosyl hydrolase.
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Related PDB
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1ex1
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Related UniProtKB
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Q9XEI3
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[4]
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Resource
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Comments
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Medline ID
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PubMed ID
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10966578
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Journal
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Proteins
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Year
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2000
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Volume
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41
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Pages
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257-69
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Authors
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Harvey AJ, Hrmova M, De Gori R, Varghese JN, Fincher GB
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Title
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Comparative modeling of the three-dimensional structures of family 3 glycoside hydrolases.
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Related PDB
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Related UniProtKB
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[5]
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Resource
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Comments
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structure-function relationships (review)
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Medline ID
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PubMed ID
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11554481
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Journal
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Plant Mol Biol
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Year
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2001
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Volume
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47
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Pages
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73-91
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Authors
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Hrmova M, Fincher GB
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Title
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Structure-function relationships of beta-D-glucan endo- and exohydrolases from higher plants.
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Related PDB
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Related UniProtKB
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[6]
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Resource
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Comments
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X-ray crystallography
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Medline ID
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PubMed ID
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11709165
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Journal
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Structure
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Year
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2001
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Volume
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9
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Pages
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1005-16
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Authors
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Hrmova M, Varghese JN, De Gori R, Smith BJ, Driguez H, Fincher GB
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Title
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Catalytic mechanisms and reaction intermediates along the hydrolytic pathway of a plant beta-D-glucan glucohydrolase.
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Related PDB
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1ieq
1iev
1iew
1iex
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Related UniProtKB
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[7]
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Resource
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Comments
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X-RAY CRYSTALLOGRAPHY (2.4 ANGSTROMS) OF 26-630.
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Medline ID
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PubMed ID
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12034895
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Journal
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Plant Cell
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Year
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2002
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Volume
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14
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Pages
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1033-52
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Authors
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Hrmova M, De Gori R, Smith BJ, Fairweather JK, Driguez H, Varghese JN, Fincher GB
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Title
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Structural basis for broad substrate specificity in higher plant beta-D-glucan glucohydrolases.
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Related PDB
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1j8v
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Related UniProtKB
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Q9XEI3
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[8]
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Resource
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Comments
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Medline ID
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PubMed ID
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12932786
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Journal
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J Mol Graph Model
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Year
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2003
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Volume
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22
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Pages
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151-9
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Authors
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Smith BJ
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Title
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Can thioglycosides imitate the oxonium intermediate in glycosyl hydrolases?
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Related PDB
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Related UniProtKB
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[9]
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Resource
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Comments
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X-RAY CRYSTALLOGRAPHY (2.7 ANGSTROMS) OF 26-627.
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Medline ID
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PubMed ID
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14597633
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Journal
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J Biol Chem
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Year
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2004
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Volume
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279
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Pages
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4970-80
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Authors
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Hrmova M, De Gori R, Smith BJ, Vasella A, Varghese JN, Fincher GB
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Title
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Three-dimensional structure of the barley beta-D-glucan glucohydrolase in complex with a transition state mimic.
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Related PDB
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1lq2
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Related UniProtKB
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Q9XEI3
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[10]
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Resource
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Comments
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X-ray crystallography
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Medline ID
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PubMed ID
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16342944
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Journal
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Biochemistry
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Year
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2005
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Volume
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44
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Pages
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16529-39
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Authors
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Hrmova M, Streltsov VA, Smith BJ, Vasella A, Varghese JN, Fincher GB
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Title
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Structural rationale for low-nanomolar binding of transition state mimics to a family GH3 beta-D-glucan glucohydrolase from barley.
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Related PDB
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1x38
1x39
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Related UniProtKB
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Comments
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This enzyme belongs to the glycosidase family-3, with a retaining mechanism.
According to the literature [1], although the reactions by this enzyme are similar to those by (1,3)-beta-glucan exohydrolases that have been classified in E.C. 3.2.1.58, this enzyme can hydrolyze substrates with linkages other than those in the (1,3)-position.
Furthermore, whilst the glycosidases that are classified in the E.C. 3.2.1.58 must have an inverting mechanism, releaseing alpha-D-Glucose, this enzyme has got a retaining mechanism, releasing beta-D-glucose. Thus, the E.C. number of this enzyme is not completely assigned yet.
According to the literature [2] & [6], the reaction of this enzyme proceeds as follows:
(1) Trp430 and Trp434 may act as modulator by increasing the pKa of Glu491, whereas Arg158 may decrease the pKa of Glu491 as a modulator.
(2) Glu491 acts as a general acid to protonate the leaving oxygen atom, leading to the formation of an oxocarbonium ion-like transition-state. Here, Asp285 may stabilize the positive charge on the C1 carbon of the oxocarbonium ion-like transition-state.
(3) Asp285 makes a nucleophilic attack on the C1 carbon, forming a glycosyl-enzyme intermediate.
(4) Glu491 acts as a general base to activate a water molecule.
(5) The activated water molecule makes a nucleophilic attack on the C1 carbon of the intermediate, completing the hydrolysis reaction through the formation of an oxocarbonium ion-like transition-state.
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