Dupuis A, Darrouzet E, Duborjal H, Pierrard B, Chevallet M, van Belzen R, Albracht S P, Lunardi J
Laboratoire de BioEnergétique Cellulaire et Pathologique, EA 2019 UJF, DBMS, CEA, Grenoble, France.
Mol Microbiol. 1998 May;28(3):531-41. doi: 10.1046/j.1365-2958.1998.00814.x.
Seven out of the 13 proteins encoded by the mitochondrial genome of mammals (peptides ND1 to ND6 plus ND4L) are subunits of the respiratory NADH-ubiquinone oxidoreductase (complex I). The function of these ND subunits is still poorly understood. We have used the NADH-ubiquinone oxidoreductase of Rhodobacter capsulatus as a model for the study of the function of these proteins. In this bacterium, the 14 genes encoding the NADH-ubiquinone oxidoreductase are clustered in the nuo operon. We report here on the biochemical and spectroscopic characterization of mutants individually disrupted in five nuo genes, equivalent to mitochondrial genes nd1, nd2, nd5, nd6 and nd4L. Disruption of any of these genes in R. capsulatus leads to the suppression of NADH dehydrogenase activity at the level of the bacterial membranes and to the disappearance of complex I-associated iron-sulphur clusters. Individual NUO subunits can still be immunodetected in the membranes of these mutants, but they do not form a functional subcomplex. In contrast to these observations, disruption of two ORFs (orf6 and orf7), also present in the distal part of the nuo operon, does not suppress NADH dehydrogenase activity or complex I-associated EPR signals, thus demonstrating that these ORFs are not essential for the biosynthesis of complex I.
哺乳动物线粒体基因组编码的13种蛋白质中有7种（肽ND1至ND6加上ND4L）是呼吸NADH-泛醌氧化还原酶（复合体I）的亚基。这些ND亚基的功能仍知之甚少。我们已将荚膜红细菌的NADH-泛醌氧化还原酶用作研究这些蛋白质功能的模型。在这种细菌中，编码NADH-泛醌氧化还原酶的14个基因聚集在nuo操纵子中。我们在此报告了分别在五个nuo基因中被破坏的突变体的生化和光谱特征，这五个基因相当于线粒体基因nd1、nd2、nd5、nd6和nd4L。荚膜红细菌中这些基因中的任何一个被破坏都会导致细菌膜水平上NADH脱氢酶活性的抑制以及复合体I相关铁硫簇的消失。在这些突变体的膜中仍可免疫检测到单个NUO亚基，但它们不会形成功能性亚复合体。与这些观察结果相反，nuo操纵子远端也存在的两个开放阅读框（orf6和orf7）被破坏不会抑制NADH脱氢酶活性或复合体I相关的电子顺磁共振信号，从而证明这些开放阅读框对于复合体I的生物合成不是必需的。
