• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Journal of Molecular Biology >Crystallographic and kinetic investigations on the mechanism of 6-pyruvoyl tetrahydropterin synthase.
【24h】

Crystallographic and kinetic investigations on the mechanism of 6-pyruvoyl tetrahydropterin synthase.

机译：晶体学和动力学研究6-丙酮酰四氢蝶呤合酶的机理。

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The enzyme 6-pyruvoyl tetrahydropterin synthase (PTPS) catalyses the second step in the de novo biosynthesis of tetrahydrobiopterin, the conversion of dihydroneopterin triphosphate to 6-pyruvoyl tetrahydropterin. The Zn and Mg-dependent reaction includes a triphosphate elimination, a stereospecific reduction of the N5-C6 double bond and the oxidation of both side-chain hydroxyl groups. The crystal structure of the inactive mutant Cys42Ala of PTPS in complex with its natural substrate dihydroneopterinetriphosphate was determined at 1.9 A resolution. Additionally, the uncomplexed enzyme was refined to 2.0 A resolution. The active site of PTPS consists of the pterin-anchoring Glu A107 neighboured by two catalytic motifs: a Zn(II) binding site and an intersubunit catalytic triad formed by Cys A42, Asp B88 and His B89. In the free enzyme the Zn(II) is in tetravalent co-ordination with three histidine ligands and a water molecule. In the complex the water is replaced by the two substrate side-chain hydroxyl groups yielding a penta-co-ordinated Zn(II) ion. The Zn(II) ion plays a crucial role in catalysis. It activates the protons of the substrate, stabilizes the intermediates and disfavours the breaking of the C1'C2' bond in the pyruvoyl side-chain. Cys A42 is activated by His B89 and Asp B88 for proton abstraction from the two different substrate side-chain atoms C1', and C2'. Replacing Ala A42 in the mutant structure by the wild-type Cys by modelling shows that the C1' and C2' substrate side-chain protons are at equal distances to Cys A42 Sgamma. The basicity of Cys A42 may be increased by a catalytic triad His B89 and Asp B88. The active site of PTPS seems to be optimised to carry out proton abstractions from two different side-chain C1' and C2' atoms, with no obvious preference for one of them. Kinetic studies with dihydroneopterin monophosphate reveal that the triphosphate moiety of the substrate is necessary for enzyme specifity. Copyright 1999 Academic Press.
机译：酶6-丙酮酰四氢蝶呤合酶（PTPS）催化四氢生物蝶呤从头生物合成的第二步，即将二氢蝶呤三磷酸转化为6-丙酮酰四氢蝶呤。依赖锌和镁的反应包括三磷酸消除，N5-C6双键的立体有择还原以及两个侧链羟基的氧化。以1.9 A的分辨率测定了PTPS的无活性突变体Cys42Ala与天然底物二氢蝶呤三磷酸复合的晶体结构。另外，将未复合的酶精制至2.0 A的分辨率。 PTPS的活性位点是由锚定于蝶呤的Glu A107组成，它与两个催化基序相邻：一个Zn（II）结合位点和一个由Cys A42，Asp B88和His B89形成的亚基间催化三联体。在游离酶中，Zn（II）与三个组氨酸配体和一个水分子处于四价配位状态。在络合物中，水被两个底物侧链羟基取代，产生五配位的Zn（II）离子。 Zn（II）离子在催化中起关键作用。它活化底物的质子，稳定中间体，不利于丙酮酰侧链中C1'C2'键的断裂。 Cys A42被His B89和Asp B88激活，用于从两个不同的底物侧链原子C1'和C2'提取质子。通过建模用野生型Cys取代突变体结构中的Ala A42，表明C1'和C2'底物侧链质子与Cys A42 Sgamma的距离相等。催化三联体His B89和Asp B88可增加Cys A42的碱性。似乎已优化了PTPS的活性位点，以从两个不同的侧链C1'和C2'原子进行质子提取，而其中之一显然没有偏爱。二氢蝶呤单磷酸的动力学研究表明，底物的三磷酸部分对于酶的特异性是必需的。版权所有1999，学术出版社。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号