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首页> 外文期刊>Acta crystallographica.Section D. Biological crystallography >Structural analysis and insights into the glycon specificity of the rice GH1 Os7BGlu26 β-d-mannosidase
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Structural analysis and insights into the glycon specificity of the rice GH1 Os7BGlu26 β-d-mannosidase

机译：结构分析和洞察glycongh Os7BGlu26特异性的大米β-d-mannosidase

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摘要

Rice Os7BGlu26 is a GH1 family glycoside hydrolase with a threefold higher k cat/K m 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 2.2014;? and of Os7BGlu26 with mannose at a resolution of 2.4514;? were elucidated from isomorphous crystals in space group P212121. The (β/)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 S 5 skew-boat conformation. Docking of the 1 S 3, 1 S 5, 2 S O and 3 S 1 pyranose-ring conformations of 4NPMan and 4NPGlc substrates into the active site of Os7BGlu26 indicated that the lowest energies were in the 1 S 5 and 1 S 3 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 k cat/K m values for 4NPMan and 4NPGlc, while mutation of Tyr134 to Phe resulted in a 37-fold higher k cat/K m 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.
机译：大米Os7BGlu26 gh家庭糖苷水解酶用三倍高k猫/ k m值4-nitrophenylβ-d-mannoside (4 npman)比较与4-nitrophenylβ-d-glucoside (4 npglc)。调查其选择性β-d-mannoside和β-d-glucoside基质,apo的结构在分辨率为2.2014;Os7BGlu26吗?Os7BGlu26与甘露糖的决议2.4514; ?晶体的空间群P212121。结构类似于其他gh的家庭结构,但窄的活性部位间隙。对应于一个产品复杂,在1 S 5β-d-mannose skew-boat构象。对接1 S的3、5 1 S, 2 S O和3 S 14 npman和4 npglc pyranose-ring构象底物的活性部位Os7BGlu26表明,能量最低的是15和1 3 skew-boat构象。这些与其他大米gh停靠矫形器结构显示不同的残留与催化酸/碱之间的交互酶有或没有β-d-mannosidase活动。Os7BGlu26导致类似k猫/ k m值4 npman和4 npglc, Tyr134突变板式换热器导致37-fold高k猫/ k m4比4 npglc npman。活性和选择性下降为β-d-mannoside。与催化酸/碱扮演的交互重要的角色在glycon选择。

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