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首页> 外文期刊>Acta crystallographica.Section D. Biological crystallography >The apo structure of sucrose hydrolase from Xanthomonas campestris pv. campestris shows an open active-site groove
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The apo structure of sucrose hydrolase from Xanthomonas campestris pv. campestris shows an open active-site groove

机译：人群的蔗糖水解酶的结构黄定pv。开放的活性部位槽

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摘要

Glycoside hydrolase family 13 (GH-13) mainly contains starch-degrading or starch-modifying enzymes. Sucrose hydrolases utilize sucrose instead of amylose as the primary glucosyl donor. Here, the catalytic properties and X-ray structure of sucrose hydrolase from Xanthomonas campestris pv. campestris are reported. Sucrose hydrolysis catalyzed by the enzyme follows Michaelis-Menten kinetics, with a Km of 60.7 mM and a kcat of 21.7 s -1. The structure of the enzyme was solved at a resolution of 1.9 ? in the resting state with an empty active site. This represents the first apo structure from subfamily 4 of GH-13. Comparisons with structures of the highly similar sucrose hydrolase from X. axonopodis pv. glycines most notably showed that residues Arg516 and Asp138, which form a salt bridge in the X. axonopodis sucrose complex and define part of the subsite -1 glucosyl-binding determinants, are not engaged in salt-bridge formation in the resting X. campestris enzyme. In the absence of the salt bridge an opening is created which gives access to subsite -1 from the 'nonreducing' end. Binding of the glucosyl moiety in subsite -1 is therefore likely to induce changes in the conformation of the active-site cleft of the X. campestris enzyme. These changes lead to salt-bridge formation that shortens the groove. Additionally, this finding has implications for understanding the molecular mechanism of the closely related subfamily 4 glucosyl transferase amylo-sucrase, as it indicates that sucrose could enter the active site from the 'nonreducing' end during the glucan-elongation cycle.
机译：糖苷水解酶家族13 (GH-13)主要包含starch-degrading或starch-modifying酶。而直链淀粉作为主要glucosyl捐献者。在这里,催化性质和x射线从植物蔗糖水解酶的结构定pv。水解酶催化的Michaelis-Menten动力学,公里的60.7毫米和kcat 21.7年代1。酶在分辨率为1.9解决了吗?静息状态和一个空的活性部位。代表第一个apo从亚结构4 GH-13。蔗糖水解酶从X高度相似。axonopodis pv。残留Arg516 Asp138,形成盐桥在x axonopodis复杂和蔗糖子站1 glucosyl-binding定义的一部分决定因素,不从事盐桥形成休息x定酶。没有盐桥开放创建使访问子站1的“nonreducing”结束。在子站1因此可能诱发活性位点的构象的变化裂的x定酶。导致盐桥形成,缩短了槽。对理解分子的影响机制密切相关的亚科4glucosyl转移酶amylo-sucrase,因为它表明,蔗糖进入活跃网站的“nonreducing”中结束glucan-elongation周期。

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