Khalimonchuk Oleh, Bird Amanda, Winge Dennis R
University of Utah Health Sciences Center, Department of Medicine, Salt Lake City, Utah 84132, USA.
J Biol Chem. 2007 Jun 15;282(24):17442-9. doi: 10.1074/jbc.M702379200. Epub 2007 Apr 12.
The hydrogen peroxide sensitivity of cells lacking two proteins, Sco1 and Cox11, important in the assembly of cytochrome c oxidase (CcO), is shown to arise from the transient accumulation of a pro-oxidant heme A-Cox1 stalled intermediate. The peroxide sensitivity of these cells is abrogated by a reduction in either Cox1 expression or heme A formation but exacerbated by either enhanced Cox1 expression or heme A production arising from overexpression of COX15. Sco1 and Cox11 are implicated in the formation of the Cu(A) and Cu(B) sites of CcO, respectively. The respective wild-type genes suppress the peroxide sensitivities of sco1Delta and cox11Delta cells, but no cross-complementation is seen with noncognate genes. Copper-binding mutant alleles of Sco1 and Cox11 that are nonfunctional in promoting the assembly of CcO are functional in suppressing the peroxide sensitivity of their respective null mutants. Likewise, human Sco1 that is nonfunctional in yeast CcO assembly is able to suppress the peroxide sensitivity of yeast sco1Delta cells. Thus, a disconnect exists between the respiratory capacity of cells and hydrogen peroxide sensitivity. Hydrogen peroxide sensitivity of sco1Delta and cox11Delta cells is abrogated by overexpression of a novel mitochondrial ATPase Afg1 that promotes the degradation of CcO mitochondrially encoded subunits. Studies on the hydrogen peroxide sensitivity in CcO assembly mutants reveal new aspects of the CcO assembly process.
缺乏两种在细胞色素c氧化酶（CcO）组装中起重要作用的蛋白质Sco1和Cox11的细胞对过氧化氢的敏感性，被证明源于一种促氧化剂血红素A - Cox1停滞中间体的短暂积累。这些细胞的过氧化物敏感性可通过降低Cox1表达或血红素A形成来消除，但因COX15过表达导致的Cox1表达增强或血红素A产生增加而加剧。Sco1和Cox11分别与CcO的Cu(A)和Cu(B)位点的形成有关。各自的野生型基因可抑制sco1Delta和cox11Delta细胞的过氧化物敏感性，但非同源基因之间未见交叉互补。在促进CcO组装方面无功能的Sco1和Cox11的铜结合突变等位基因，在抑制其各自缺失突变体的过氧化物敏感性方面具有功能。同样，在酵母CcO组装中无功能的人类Sco1能够抑制酵母sco1Delta细胞的过氧化物敏感性。因此，细胞的呼吸能力与过氧化氢敏感性之间存在脱节。通过过表达一种促进线粒体编码的CcO亚基降解的新型线粒体ATP酶Afg1，可消除sco1Delta和cox11Delta细胞的过氧化氢敏感性。对CcO组装突变体中过氧化氢敏感性的研究揭示了CcO组装过程的新方面。
