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PDBsum entry 1cb2
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Hydrolase (o-glycosyl)
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PDB id
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1cb2
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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The active site of trichoderma reesei cellobiohydrolase ii: the role of tyrosine 169.
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Authors
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A.Koivula,
T.Reinikainen,
L.Ruohonen,
A.Valkeajärvi,
M.Claeyssens,
O.Teleman,
G.J.Kleywegt,
M.Szardenings,
J.Rouvinen,
T.A.Jones,
T.T.Teeri.
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Ref.
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Protein Eng, 1996,
9,
691-699.
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PubMed id
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Abstract
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Trichoderma reesei cellobiohydrolase II (CBHII) is an exoglucanase cleaving
primarily cellobiose units from the non-reducing end of cellulose chains. The
beta-1,4 glycosidic bond is cleaved by acid catalysis with an aspartic acid,
D221, as the likely proton donor, and another aspartate, D175, probably ensuring
its protonation and stabilizing charged reaction intermediates. The catalytic
base has not yet been identified experimentally. The refined crystal structure
of CBHII also shows a tyrosine residue, Y169, located close enough to the
scissile bond to be involved in catalysis. The role of this residue has been
studied by introducing a mutation Y169F, and analysing the kinetic and binding
behavior of the mutated CBHII. The crystal structure of the mutated enzyme was
determined to 2.0 A resolution showing no changes when compared with the
structure of native CBHII. However, the association constants of the mutant
enzyme for cellobiose and cellotriose are increased threefold and for
4-methylumbelliferyl cellobioside over 50-fold. The catalytic constants towards
cellotriose and cellotetraose are four times lower for the mutant. These data
suggest that Y169, on interacting with a glucose ring entering the second
subsite in a narrow tunnel, helps to distort the glucose ring into a more
reactive conformation. In addition, a change in the pH activity profile was
observed. This indicates that Y169 may have a second role in the catalysis,
namely to affect the protonation state of the active site carboxylates, D175 and
D221.
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Secondary reference #1
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Title
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Three-Dimensional structure of cellobiohydrolase ii from trichoderma reesei.
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Authors
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J.Rouvinen,
T.Bergfors,
T.Teeri,
J.K.Knowles,
T.A.Jones.
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Ref.
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Science, 1990,
249,
380-386.
[DOI no: ]
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PubMed id
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