Augmenter of liver regeneration:: A flavin-dependent sulfhydryl oxidase with cytochrome c reductase activity
Augmenter of liver regeneration:: A flavin-dependent sulfhydryl oxidase with cytochrome c reductase activity
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DOI：
10.1021/bi0479555
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发表时间：
2005-02-08
期刊：
影响因子：
2.9
通讯作者：
Thorpe, C
中科院分区：
文献类型：
--
作者：
Farrell, SR;Thorpe, C
肝再生增强因子（ALR; hepatopoietin）是近年来发现的一种与黄素连接的巯基氧化酶。一个N-末端组氨酸标记的结构的短形式的人蛋白质已在大肠杆菌中过表达。与最近的报道相反，几条证据表明，人ALR是一种二硫键桥接的二聚体（通过C15-C124连接），每个单体有两个游离半胱氨酸残基（C74和85）。C15-124二硫化物对于二聚体形成不是关键的，并且对ALR的二硫苏糖醇（DTT）氧化酶活性具有不显著的影响。尽管大鼠ALR的晶体结构显示近端二硫化物（C62-C65）准备与FAD辅基相互作用[Wu，C. K.，戴利，T。A.、戴利，H。一、Wang，B. C.的方法，和Rose，J.P.（2003）Protein Sci. 12，1109-1118]，在酶的氧化还原滴定期间仅黄素还原是明显的。ALR与DTT在有氧周转过程中形成大量的中性半醌。这种半醌部分是由二聚体内黄素中心之间的歧化作用产生的。令人惊讶的是，当DTT是还原底物时，细胞色素c是ALR的电子受体比氧好约100倍。这些数据表明，这种知之甚少的黄素酶可能不作为线粒体膜间隙内的巯基氧化酶，但可能通过细胞色素c的介导与呼吸链沟通。
Augmenter of liver regeneration (ALR; hepatopoietin) is a recently discovered enigmatic flavin-linked sulfhydryl oxidase. An N-terminal His-tagged construct of the short form of the human protein has been overexpressed in Escherichia coli. Several lines of evidence suggest that, contrary to a recent report, human ALR is a disulfide-bridged dimer (linked via C15-C124) with two free cysteine residues (C74 and 85) per monomer. The C15-124 disulfides are not critical for dimer formation and have insignificant impact on the dithiothreitol (DTT) oxidase activity of ALR. Although the crystal structure of rat ALR shows a proximal disulfide (C62-C65) poised to interact with the FAD prosthetic group [Wu, C. K., Dailey, T. A., Dailey, H. A., Wang, B. C., and Rose, J. P. (2003) Protein Sci. 12, 1109-1118], only flavin reduction is evident during redox titrations of the enzyme. ALR forms large amounts of neutral semiquinone during aerobic turnover with DTT. This semiquinone arises, in part, by comproportionation between flavin centers within the dimer. Surprisingly, cytochrome c is about a 100-fold better electron acceptor for ALR than oxygen when DTT is the reducing substrate. These data suggest that this poorly understood flavoenzyme may not function as a sulfhydryl oxidase within the mitochondrial intermembrane space but may communicate with the respiratory chain via the mediation of cytochrome c.