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首页> 外文期刊>Biochemistry >A New Electron Transport Mechanism in Mitochondrial Steroid Hydroxylase Systems Based on Structural Changes upon the Reduction of Adrenodoxin
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A New Electron Transport Mechanism in Mitochondrial Steroid Hydroxylase Systems Based on Structural Changes upon the Reduction of Adrenodoxin

机译：基于肾上腺毒素还原的结构变化的线粒体甾体羟化酶系统新的电子传输机理

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摘要

The adrenal ferredoxin (adrenodoxin, Adx) is an acidic 14.4-kDa [2Fe-2S] ferredoxin that belongs to the vertebrate ferredoxin family. It is involved in the electron transfer from the flavoenzyme NADPH-adrenodoxin-reductase to cytochromes P-450_scc and P-450_11#beta#. The interaction between the redox partners during electron transport has not yet been fully established. Determining the tertiary strufture of an electron-transfer protein may be very helpful in understanding the transport mechanism. In the present work, we report a structural study on the oxidized and reduced forms of bovine adrenodoxin (bAdx) in solution using high-resolution NMR spectroscopy. The protein was produced in Escherichia coli and singly or doubly labeled with ~15N or ~13C/~15N, respectively. Aproximately 70 and 75% of the ~15N, ~13C, and ~1H resonances could be assigned for the reduced and the oxidized bAdx, respectively. The secondary and tertiary structures of the reduced and oxidized states were determined using NOE distancce information. ~1H_N-T_1 relaxation times of certain residues were used to obtain additional distance constraints t the [2Fe-2S] cluster. The results suggest that the solution structure of oxidized Adx is quite similar to the X-ray structure. However, structural changes occur upon reduction of the [2Fe-2S] cluster, as indicated by NMR measurements. It could be shown that these conformational changes, especially in the C-terminal region, cause the dissociation of the Adx dimer upon reduction. A new electron transport mechanism proceeding via a modified shuttle mechanism, with both monomers and dimers acting as electron carriers, is proposed.
机译：肾上腺铁氧还蛋白（adrenodoxin，Adx）是一种酸性14.4kDa [2Fe-2S]铁氧还蛋白，属于脊椎动物铁氧还蛋白家族。它参与了从黄素酶NADPH-肾上腺素还原酶到细胞色素P-450_scc和P-450_11＃beta＃的电子转移。电子传输过程中氧化还原伙伴之间的相互作用尚未完全建立。确定电子转移蛋白的三级结构可能对理解转运机制非常有帮助。在目前的工作中，我们报告使用高分辨率NMR光谱对溶液中牛肾上腺毒素（bAdx）的氧化和还原形式进行结构研究。该蛋白质在大肠杆菌中产生，分别用〜15N或〜13C /〜15N单独或双重标记。 〜15N，〜13C和〜1H共振的大约70％和75％可以分别分配给还原的bAdx和氧化的bAdx。使用NOE区别信息确定还原态和氧化态的二级和三级结构。某些残基的〜1H_N-T_1弛豫时间用于获得[2Fe-2S]簇的附加距离约束。结果表明，氧化的Adx的溶液结构与X射线结构非常相似。然而，如NMR测量所示，在[2Fe-2S]簇减少时会发生结构变化。可以证明，这些构象变化，特别是在C-末端区域，在还原时引起Adx二聚体的离解。提出了一种新的电子传输机制，该机制通过修饰的穿梭机制进行，单体和二聚体均充当电子载体。

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