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Publication Abstract from PubMed

Rice Os7BGlu26 is a GH1 family glycoside hydrolase with a threefold higher kcat/Km value for 4-nitrophenyl beta-D-mannoside (4NPMan) compared with 4-nitrophenyl beta-D-glucoside (4NPGlc). To investigate its selectivity for beta-D-mannoside and beta-D-glucoside substrates, the structures of apo Os7BGlu26 at a resolution of 2.20 A and of Os7BGlu26 with mannose at a resolution of 2.45 A were elucidated from isomorphous crystals in space group P212121. The (beta/alpha)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 beta-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 beta-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 beta-D-mannoside. It was concluded that interactions with the catalytic acid/base play a significant role in glycon selection.

Structural analysis and insights into the glycon specificity of the rice GH1 Os7BGlu26 beta-D-mannosidase.,Tankrathok A, Iglesias-Fernandez J, Luang S, Robinson RC, Kimura A, Rovira C, Hrmova M, Ketudat Cairns JR Acta Crystallogr D Biol Crystallogr. 2013 Oct;69(Pt 10):2124-35. doi:, 10.1107/S0907444913020568. Epub 2013 Sep 20. PMID:24100330^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.