Emmermann M, Braun H P, Arretz M, Schmitz U K
Institut für Genbiologische Forschung Berlin GmbH, Germany.
J Biol Chem. 1993 Sep 5;268(25):18936-42.
In potato, cytochrome c reductase, a protein complex of the respiratory chain, exhibits processing activity toward mitochondrial precursor proteins. One of the two cooperating components of the processing peptidase was shown to be identical with subunit III of the complex. Here we report that two additional proteins of the complex (subunit I and II) share 40-50% sequence identity with the processing enhancing protein, the other component of the processing enzyme from fungi and mammals. Thus the composition and structure of the complex integrated processing peptidase seems to be different from its fungal and mammalian counterparts. Cytochrome c reductase from potato is extraordinarily stable, and separation of subunit III from the complex leads to aggregation of the remaining subcomplex and irreversible loss of processing activity. Expression of the three high molecular weight subunits of the complex allowed purification of each individual protein. Neither the individual subunits nor their combinations are active in in vitro processing assays suggesting that they may need the structural support of the complex for activity. In contrast to mitochondrial processing peptidases from other organisms, the purified potato enzyme is active in the presence of high salt (above 1 M NaCl) and works efficiently without addition of metal ions. These data indicate that potato cytochrome c reductase is a bifunctional protein complex with unique features. Possibly, there is a more general evolutionary relationship between cytochrome c reductases and mitochondrial processing peptidases than hitherto assumed.
在马铃薯中，细胞色素c还原酶作为呼吸链的一种蛋白质复合体，对线粒体前体蛋白具有加工活性。加工肽酶的两个协同组分之一被证明与该复合体的亚基III相同。在此，我们报道该复合体的另外两种蛋白质（亚基I和II）与加工增强蛋白具有40 - 50%的序列同一性，加工增强蛋白是真菌和哺乳动物加工酶的另一个组分。因此，整合加工肽酶的复合体的组成和结构似乎不同于其真菌和哺乳动物的对应物。马铃薯的细胞色素c还原酶极其稳定，从复合体中分离亚基III会导致其余亚复合体聚集以及加工活性的不可逆丧失。该复合体三个高分子量亚基的表达使得能够纯化每种单独的蛋白质。在体外加工试验中，单独的亚基及其组合均无活性，这表明它们可能需要复合体的结构支持才能发挥活性。与其他生物体的线粒体加工肽酶不同，纯化后的马铃薯酶在高盐（高于1 M NaCl）存在的情况下具有活性，并且在不添加金属离子的情况下也能高效发挥作用。这些数据表明马铃薯细胞色素c还原酶是一种具有独特特征的双功能蛋白质复合体。可能，细胞色素c还原酶与线粒体加工肽酶之间的进化关系比迄今所认为的更为普遍。
