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PDBsum entry 4jie
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References listed in PDB file
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Key reference
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Title
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Structural analysis and insights into the glycon specificity of the rice gh1 os7bglu26 β-D-Mannosidase.
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Authors
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A.Tankrathok,
J.Iglesias-Fernández,
S.Luang,
R.C.Robinson,
A.Kimura,
C.Rovira,
M.Hrmova,
J.R.Ketudat cairns.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2013,
69,
2124-2135.
[DOI no: ]
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PubMed id
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Abstract
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Rice Os7BGlu26 is a GH1 family glycoside hydrolase with a threefold higher
kcat/Km value for 4-nitrophenyl β-D-mannoside (4NPMan) compared with
4-nitrophenyl β-D-glucoside (4NPGlc). To investigate its selectivity for
β-D-mannoside and β-D-glucoside substrates, the structures of apo Os7BGlu26 at
a resolution of 2.20 Å and of Os7BGlu26 with mannose at a resolution of
2.45 Å were elucidated from isomorphous crystals in space group P212121. The
(β/α)8-barrel structure is similar to other GH1 family structures, but with a
narrower active-site cleft. The Os7BGlu26 structure with D-mannose corresponds
to a product complex, with β-D-mannose in the (1)S5 skew-boat conformation.
Docking of the (1)S3, (1)S5, (2)SO and (3)S1 pyranose-ring conformations of
4NPMan and 4NPGlc substrates into the active site of Os7BGlu26 indicated that
the lowest energies were in the (1)S5 and (1)S3 skew-boat conformations.
Comparison of these docked conformers with other rice GH1 structures revealed
differences in the residues interacting with the catalytic acid/base between
enzymes with and without β-D-mannosidase activity. The mutation of Tyr134 to
Trp in Os7BGlu26 resulted in similar kcat/Km values for 4NPMan and 4NPGlc, while
mutation of Tyr134 to Phe resulted in a 37-fold higher kcat/Km for 4NPMan than
4NPGlc. Mutation of Cys182 to Thr decreased both the activity and the
selectivity for β-D-mannoside. It was concluded that interactions with the
catalytic acid/base play a significant role in glycon selection.
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