An intragenic suppressor in the cytochrome c oxidase I gene of mouse mitochondrial DNA

Abstract

We report here the identification of a cell line containing single and double missense mutations in cytochrome c oxidase (COX) subunit I gene of mouse mitochondrial DNA. When present in homoplasmy, the single mutant displays a normal complex IV assembly but a significantly reduced COX activity, while the double mutant almost completely compensates the functional defect of the first mutation. We discuss the potential structural consequences of those mutations based on the modeled structure of mouse complex IV. Based on genetic, biochemical and molecular analyses of cultured mouse cells we infer that: (i) deleterious mutations can arise and become predominant; (ii) cultured cells can maintain several mtDNA haplotypes at stable frequencies; (iii) the respiratory chain has little spare COX capacity; and (iv) the size of a cavity in the vicinity of Val421 in CO I of animal COX may affect the function of the enzyme.

ROS-Triggered Phosphorylation of Complex II by Fgr Kinase Regulates Cellular Adaptation to Fuel Use

“…As reported (Acín-Pérez et al, 2003; Bai and Attardi, 1998), the amount of CI was reduced in cells with a high ND6 mutant load (FG12-1, FG23-1; Figure 1C, upper panel), whereas CII content was unchanged, despite above-normal activity determined spectrophotometrically (Figure 1B) and by in-gel assay (data not shown). G3PDH activity did not differ between WT and ND6 mutants (Figure 1D), indicating that increased CII activity does not reflect a generalized response of enzymes that donate electrons to CIII and is a specific response to CI deficiency.…”

“…Our laboratory has isolated mouse cell lines carrying different proportions of a null ND6 mutation (Acín-Pérez et al, 2003): EB2615 (30% mutant mtDNA), E23 (66%), E12 (80%), FG12-1 (95%), and FG23-1 (98%). Mitochondria from ND6 mutants showed reductions in CI proportional to the mutation load (Figure 1A).…”

Phosphorylation of Mammalian Cytochrome c and Cytochrome c Oxidase in the Regulation of Cell Destiny: Respiration, Apoptosis, and Human Disease

“…In mammals, it is the proposed rate-limiting step of the ETC in intact cells (Villani et al 1997; Villani et al 1998; Acin-Perez et al 2003; Piccoli et al 2006; Dalmonte et al 2009; Pacelli et al 2011), but not in isolated mitochondria. The latter phenomenon may be explained by unsuitable mitochondria isolation methods, which disrupt cellular structures and signaling networks, leading to a loss of regulatory properties of COX and Cytc, likely via dephosphorylation reactions.…”

Mice deleted for heart-type cytochrome c oxidase subunit 7a1 develop dilated cardiomyopathy

“…Cytochrome c oxidase (Cox), the terminal protein complex of the mitochondrial electron transport chain (ETC), consists of 13 proteins, 3 encoded by the mitochondrial genome and 10 encoded by the nuclear genome. Cox is the proposed rate-limiting enzyme of the ETC in intact cells (Villani et al, 2003; Acin-Perez et al, 2003), and it contains at least five subunits with tissue-specific isoforms, uniquely among the electron transport complexes, suggesting a regulatory role in modulating energy metabolism. These are Cox4i1/Cox4i2; Cox6a1/Cox6a2; Cox6b1/Cox6b2; Cox7a1/Cox7a2; Cox8a/Cox8b/Cox8c.…”