Atomic Structure of Salutaridine Reductase from the Opium Poppy (Papaver somniferum)
Atomic Structure of Salutaridine Reductase from the Opium Poppy (Papaver somniferum)
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DOI：
10.1074/jbc.m110.168633
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发表时间：
2011-02-25
影响因子：
4.8
通讯作者：
Smith, Thomas J.
中科院分区：
文献类型：
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作者：
Higashi, Yasuhiro;Kutchan, Toni M.;Smith, Thomas J.
罂粟(Papaver Somniferum L.)是已知最古老的药用植物之一。在吗啡和可待因的生物合成途径中，以NADPH为辅酶的Salutaridine还原酶(SalR；EC 1.1.1.248)将其还原为Salutaridinol。在这里，我们报道了在NADPH存在下SalR的原子结构，其分辨率类似于1.9埃。核心结构与短链脱氢酶/还原酶家族的其他成员高度同源。主要的区别是烟酰胺部分和底物结合口袋被一个环(残基265-279)覆盖，其上有一个大的“瓣状”结构域(残基105-140)。这种构型似乎是在短链脱氢酶/还原酶家族的其他成员中发现的两个常见结构主题的组合。以往的模拟研究表明，底物抑制是由于活性部位底物结合的生产性和非生产性相互排斥的模式所致。这个模型是通过定点突变进行测试的，其中一些突变消除了底物抑制。然而，SalR的原子结构表明，这些突变残基分布在酶的广泛区域，其中许多不在活性部位。为了解释活性中心远端的残基如何影响催化，提出了一个模型，在该模型中，SalR在催化周转过程中可能经历显著的构象变化。
The opium poppy (Papaver somniferum L.) is one of the oldest known medicinal plants. In the biosynthetic pathway for morphine and codeine, salutaridine is reduced to salutaridinol by salutaridine reductase (SalR; EC 1.1.1.248) using NADPH as coenzyme. Here, we report the atomic structure of SalR to a resolution of similar to 1.9 angstrom in the presence of NADPH. The core structure is highly homologous to other members of the short chain dehydrogenase/reductase family. The major difference is that the nicotinamide moiety and the substrate-binding pocket are covered by a loop (residues 265-279), on top of which lies a large "flap"-like domain (residues 105-140). This configuration appears to be a combination of the two common structural themes found in other members of the short chain dehydrogenase/reductase family. Previous modeling studies suggested that substrate inhibition is due to mutually exclusive productive and nonproductive modes of substrate binding in the active site. This model was tested via site-directed mutagenesis, and a number of these mutations abrogated substrate inhibition. However, the atomic structure of SalR shows that these mutated residues are instead distributed over a wide area of the enzyme, and many are not in the active site. To explain how residues distal to the active site might affect catalysis, a model is presented whereby SalR may undergo significant conformational changes during catalytic turnover.