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Title: Structural analysis and insights into the glycon specificity of the rice GH1 Os7BGlu26 β-D-mannosidase
Authors: Robinson, Robert Charles
Tankrathok, Anupong
Iglesias-Fernández, Javier
Luang, Sukanya
Kimura, Atsuo
Rovira, Carme
Hrmova, Maria
Ketudat Cairns, James R.
Keywords: Structural analysis
Glycoside hydrolases
Issue Date: 2013
Source: Tankrathok, A., Iglesias-Fernández, J., Luang, S., Robinson, R. C., Kimura, A., Rovira, C., et al. (2013). Structural analysis and insights into the glycon specificity of the rice GH1 Os7BGlu26 β-D-mannosidase. Acta Crystallographica Section D Biological Crystallography, 69(10), 2124-2135.
Series/Report no.: Acta Crystallographica Section D Biological Crystallography
Abstract: 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 1S5 skew-boat conformation. Docking of the 1S3, 1S5, 2SO and 3S1 pyranose-ring conformations of 4NPMan and 4NPGlc substrates into the active site of Os7BGlu26 indicated that the lowest energies were in the 1S5 and 1S3 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.
ISSN: 0907-4449
DOI: 10.1107/S0907444913020568
Schools: School of Biological Sciences 
Rights: © 2013 International Union of Crystallography.
Fulltext Permission: none
Fulltext Availability: No Fulltext
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