Structural basis for the specificity of the reducing end xylose-releasing exo-oligoxylanase from Bacillus halodurans C-125
Structural basis for the specificity of the reducing end xylose-releasing exo-oligoxylanase from Bacillus halodurans C-125
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DOI：
10.1074/jbc.m413693200
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发表时间：
2005-04-29
影响因子：
4.8
通讯作者：
Kitaoka, M
中科院分区：
文献类型：
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作者：
Fushinobu, S;Hidaka, M;Kitaoka, M
来自耐盐芽孢杆菌C-125（雷克斯）的还原端木糖释放外切低聚木聚糖酶水解聚合度大于或等于3的低聚木糖，在还原端释放木糖单元。它是一种独特的外切型糖苷水解酶，以非常严格的方式识别还原末端的木糖单元，甚至将β-端基异构体羟基构型与α-端基异构体或1-脱氧木糖区分开。我们已经确定了雷克斯在unliganded和复杂的形式在1.35 - 2.20埃分辨率的晶体结构，并揭示了其三个子网站的结构方面，从-2到+1。将雷克斯的结构与糖苷水解酶亚家族8a（GH-8a）的内切型酶的结构进行了比较。雷克斯的催化机制与其他GH-8a酶基本上是保守的。然而，亚位点+2被螺旋α（10）前环中的扭结形成的屏障阻断。该环中的His-319在亚位点+1处与木糖的β-羟基形成直接氢键，有助于在还原末端特异性识别端基异构体。
Reducing end xylose-releasing exo-oligoxylanase from Bacillus halodurans C-125 (Rex) hydrolyzes xylooligosaccharides whose degree of polymerization is greater than or equal to 3, releasing the xylose unit at the reducing end. It is a unique exo-type glycoside hydrolase that recognizes the xylose unit at the reducing end in a very strict manner, even discriminating the beta-anomeric hydroxyl configuration from the alpha-anomer or 1-deoxyxylose. We have determined the crystal structures of Rex in unliganded and complex forms at 1.35 - 2.20-angstrom resolution and revealed the structural aspects of its three subsites ranging from - 2 to + 1. The structure of Rex was compared with those of endo-type enzymes in glycoside hydrolase subfamily 8a (GH-8a). The catalytic machinery of Rex is basically conserved with other GH-8a enzymes. However, subsite + 2 is blocked by a barrier formed by a kink in the loop before helix alpha(10). His-319 in this loop forms a direct hydrogen bond with the beta-hydroxyl of xylose at subsite + 1, contributing to the specific recognition of anomers at the reducing end.