Carroll Joe, Fearnley Ian M, Skehel J Mark, Runswick Michael J, Shannon Richard J, Hirst Judy, Walker John E
The Medical Research Council Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom.
Mol Cell Proteomics. 2005 May;4(5):693-9. doi: 10.1074/mcp.M500014-MCP200. Epub 2005 Feb 22.
Bovine complex I is an assembly of 46 different proteins. Seven of them are encoded in mitochondrial DNA, and the rest are nuclear gene products that are imported into the organelle. Fourteen of the nuclear encoded subunits have modified N termini. Many of these post-translational modifications have been deduced previously from intact protein masses. These assignments have been verified by mass spectrometric analysis of peptides. Thirteen of them are N-alpha-acetylated, and a 14th, subunit B18, is N-alpha-myristoylated. Subunit B18 forms part of the membrane arm of the complex, and the myristoyl group may attach subunit B18 to the membrane. One subunit, B12, has a particularly complex pattern of post-translational modification that has not been analyzed before. It is a mixture of the N-alpha-acetylated form and the form with a free N terminus. In addition, it has one, two, or three methyl groups attached to histidine residues at positions 4, 6, and 8 in various combinations. The predominant form is methylated on residues 4 and 6. There is no evidence for the methylation of histidine 2. Subunit B12 is also part of the membrane arm of complex I, and it probably spans the membrane once, but as its orientation is not known, the methylation sites could be in either the matrix or the intermembrane space. These experiments represent another significant step toward establishing the precise chemical composition of mammalian complex I.
牛复合体I由46种不同的蛋白质组成。其中7种由线粒体DNA编码，其余是导入该细胞器的核基因产物。14个核编码亚基具有修饰的N端。这些翻译后修饰中的许多先前已从完整蛋白质质量中推导出来。这些归属已通过肽的质谱分析得到验证。其中13个是N-α-乙酰化的，第14个亚基B18是N-α-肉豆蔻酰化的。亚基B18构成该复合体膜臂的一部分，肉豆蔻酰基团可能将亚基B18附着于膜上。一个亚基B12具有特别复杂的翻译后修饰模式，之前尚未进行分析。它是N-α-乙酰化形式和具有游离N端形式的混合物。此外，它在第4、6和8位的组氨酸残基上以各种组合连接有一个、两个或三个甲基基团。主要形式是在第4和6位残基上甲基化。没有证据表明组氨酸2发生甲基化。亚基B12也是复合体I膜臂的一部分，它可能跨膜一次，但由于其取向未知，甲基化位点可能在基质或膜间隙中。这些实验是朝着确定哺乳动物复合体I的精确化学组成迈出的又一重要一步。
