Gencic S, Schägger H, von Jagow G
Institut für Therapeutische Biochemie, Universitätsklinikum Frankfurt, Federal Republic of Germany.
Eur J Biochem. 1991 Jul 1;199(1):123-31. doi: 10.1111/j.1432-1033.1991.tb16099.x.
Core I and core II proteins are the largest nuclear-encoded subunits of the mitochondrial ubiquinol-cytochrome-c reductase (bc1 complex) lacking redox prosthetic groups. cDNA clones of the two bovine core proteins have been isolated by the screening of lambda ZAP cDNA libraries either with an oligonucleotide probe based on the sequence of an internal peptide or with a polymerase-chain-reaction-amplified fragment. The core I precursor protein consists of 362 amino acids with a 34-amino-acid presequence typical for mitochondrial targeting signals. The mature protein migrates in SDS/polyacrylamide gels with an apparent molecular mass of 47 kDa, which does not correspond to the actual molecular mass of the protein of 35.8 kDa deduced from the cDNA sequence. The core II precursor protein is composed of 453 amino acids having a 14-amino-acid presequence as a targeting sequence. Comparison of the core I amino acid sequence with sequences of the newly discovered protein family [Schulte, U., Arretz, M., Schneider, H., Tropschug, M., Wachter E., Neupert, W. & Weiss, H. (1989) Nature 339, 147 - 149] comprising the processing enhancing protein (PEP), matrix processing peptidase (MPP), and core I and II proteins from Neurospora crassa and Saccharomyces cerevisiae, revealed a remarkable identity of 39% and a high similarity of 49% to N. crassa PEP, which in this fungus is identical to core I. Core II protein is only a distant relative of this protein family. Based on these sequence comparisons and data obtained by genomic Southern blots, we anticipate that the bovine core I subunit, like the N. crassa core I protein, is bifunctional, being responsible for the maintenance of electron transport and processing of proteins during their import into the mitochondrial matrix. The analysis of the primary structure of the two core proteins completes the set of primary structures of all subunits of bovine ubiquinol-cytochrome-c reductase.
核心I蛋白和核心II蛋白是线粒体泛醇-细胞色素c还原酶（bc1复合体）中最大的核编码亚基，缺乏氧化还原辅基。通过用基于内部肽序列的寡核苷酸探针或用聚合酶链反应扩增片段筛选λZAP cDNA文库，已分离出两种牛核心蛋白的cDNA克隆。核心I前体蛋白由362个氨基酸组成，带有一个34个氨基酸的前导序列，这是线粒体靶向信号的典型特征。成熟蛋白在SDS/聚丙烯酰胺凝胶中的迁移表观分子量为47 kDa，这与从cDNA序列推导的该蛋白实际分子量35.8 kDa不相符。核心II前体蛋白由453个氨基酸组成，有一个14个氨基酸的前导序列作为靶向序列。将核心I氨基酸序列与新发现的蛋白质家族[舒尔特，U.，阿雷茨，M.，施耐德，H.，特罗普舒格，M.，瓦赫特，E.，诺伊佩特，W. & 魏斯，H.（1989年）《自然》339，147 - 149]的序列进行比较，该家族包括加工增强蛋白（PEP）、基质加工肽酶（MPP）以及来自粗糙脉孢菌和酿酒酵母的核心I和II蛋白，结果显示与粗糙脉孢菌PEP有39%的显著同一性和49%的高度相似性，在这种真菌中PEP与核心I相同。核心II蛋白只是这个蛋白质家族的远亲。基于这些序列比较和基因组Southern印迹获得的数据，我们预计牛核心I亚基，像粗糙脉孢菌核心I蛋白一样，具有双功能，在蛋白质导入线粒体基质过程中负责维持电子传递和蛋白质加工。对这两种核心蛋白一级结构的分析完成了牛泛醇-细胞色素c还原酶所有亚基一级结构的研究。
