Cytochrome c oxidase (COX), the terminal enzyme of mitochondrial electron transport chain, couples electron transport to oxygen with generation of proton gradient indispensable for the production of vast majority of ATP molecules in mammalian cells. The review summarizes current knowledge of COX structure and function of nuclear-encoded COX subunits, which may modulate enzyme activity according to various conditions. Moreover, some nuclear-encoded subunits posess tissue-specific and development-specific isoforms, possibly enabling fine-tuning of COX function in individual tissues. The importance of nuclear-encoded subunits is emphasized by recently discovered pathogenic mutations in patients with severe mitopathies. In addition, proteins substoichiometrically associated with COX were found to contribute to COX activity regulation and stabilization of the respiratory supercomplexes. Based on the summarized data, a model of three levels of quaternary COX structure is postulated. Individual structural levels correspond to subunits of the i) catalytic center, ii) nuclear-encoded stoichiometric subunits and iii) associated proteins, which may constitute several forms of COX with varying composition and differentially regulated function.

• MeSH
• Cell Nucleus enzymology   genetics   MeSH
• Genome MeSH
• Humans MeSH
• Mitochondrial Diseases enzymology   pathology   MeSH
• Mitochondria enzymology   genetics   MeSH
• Organ Specificity MeSH
• Protein Subunits MeSH
• Electron Transport Complex IV genetics   metabolism   MeSH
• Signal Transduction MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Protein Subunits MeSH
• Electron Transport Complex IV MeSH

Mitochondrial protein SURF1 is a specific assembly factor of cytochrome c oxidase (COX), but its function is poorly understood. SURF1 gene mutations cause a severe COX deficiency manifesting as the Leigh syndrome in humans, whereas in mice SURF1(-/-) knockout leads only to a mild COX defect. We used SURF1(-/-) mouse model for detailed analysis of disturbed COX assembly and COX ability to incorporate into respiratory supercomplexes (SCs) in different tissues and fibroblasts. Furthermore, we compared fibroblasts from SURF1(-/-) mouse and SURF1 patients to reveal interspecies differences in kinetics of COX biogenesis using 2D electrophoresis, immunodetection, arrest of mitochondrial proteosynthesis and pulse-chase metabolic labeling. The crucial differences observed are an accumulation of abundant COX1 assembly intermediates, low content of COX monomer and preferential recruitment of COX into I-III2-IVn SCs in SURF1 patient fibroblasts, whereas SURF1(-/-) mouse fibroblasts were characterized by low content of COX1 assembly intermediates and milder decrease in COX monomer, which appeared more stable. This pattern was even less pronounced in SURF1(-/-) mouse liver and brain. Both the control and SURF1(-/-) mice revealed only negligible formation of the I-III2-IVn SCs and marked tissue differences in the contents of COX dimer and III2-IV SCs, also less noticeable in liver and brain than in heart and muscle. Our studies support the view that COX assembly is much more dependent on SURF1 in humans than in mice. We also demonstrate markedly lower ability of mouse COX to form I-III2-IVn supercomplexes, pointing to tissue-specific and species-specific differences in COX biogenesis.

• Keywords
• Cytochrome c oxidase, Doxycycline, Leigh syndrome, Pulse-chase, Respiratory supercomplexes, SURF1(−/−) mouse knockout,
• MeSH
• Species Specificity MeSH
• Fibroblasts metabolism   pathology   MeSH
• Leigh Disease genetics   metabolism   pathology   MeSH
• Humans MeSH
• Membrane Proteins genetics   metabolism   MeSH
• Mitochondrial Proteins genetics   metabolism   MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Organ Specificity MeSH
• Electron Transport Complex IV genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Membrane Proteins MeSH
• Mitochondrial Proteins MeSH
• Electron Transport Complex IV MeSH
• Surf-1 protein MeSH Browser

Mitochondrial ATPases associated with diverse cellular activities (AAA) proteases are involved in the quality control and processing of inner-membrane proteins. Here we investigate the cellular activities of YME1L, the human orthologue of the Yme1 subunit of the yeast i-AAA complex, using stable short hairpin RNA knockdown and expression experiments. Human YME1L is shown to be an integral membrane protein that exposes its carboxy-terminus to the intermembrane space and exists in several complexes of 600-1100 kDa. The stable knockdown of YME1L in human embryonic kidney 293 cells led to impaired cell proliferation and apoptotic resistance, altered cristae morphology, diminished rotenone-sensitive respiration, and increased susceptibility to mitochondrial membrane protein carbonylation. Depletion of YME1L led to excessive accumulation of nonassembled respiratory chain subunits (Ndufb6, ND1, and Cox4) in the inner membrane. This was due to a lack of YME1L proteolytic activity, since the excessive accumulation of subunits was reversed by overexpression of wild-type YME1L but not a proteolytically inactive YME1L variant. Similarly, the expression of wild-type YME1L restored the lamellar cristae morphology of YME1L-deficient mitochondria. Our results demonstrate the importance of mitochondrial inner-membrane proteostasis to both mitochondrial and cellular function and integrity and reveal a novel role for YME1L in the proteolytic regulation of respiratory chain biogenesis.

• MeSH
• Apoptosis MeSH
• ATPases Associated with Diverse Cellular Activities MeSH
• Gene Knockdown Techniques MeSH
• GTP Phosphohydrolases metabolism   MeSH
• Humans MeSH
• Metalloendopeptidases metabolism   MeSH
• Mitochondrial Membranes metabolism   MeSH
• Mitochondrial Proteins MeSH
• Mitochondria metabolism   MeSH
• NADH, NADPH Oxidoreductases metabolism   MeSH
• Cell Proliferation * MeSH
• ATP-Dependent Proteases metabolism   MeSH
• Peptide Hydrolases metabolism   MeSH
• Protein Isoforms metabolism   MeSH
• Electron Transport Complex I MeSH
• Electron Transport Complex IV metabolism   MeSH
• Saccharomyces cerevisiae Proteins metabolism   MeSH
• Saccharomyces cerevisiae cytology   metabolism   MeSH
• Electron Transport * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• ATPases Associated with Diverse Cellular Activities MeSH
• GTP Phosphohydrolases MeSH
• Metalloendopeptidases MeSH
• Mitochondrial Proteins MeSH
• NADH, NADPH Oxidoreductases MeSH
• NDUFB6 protein, human MeSH Browser
• OPA1 protein, human MeSH Browser
• ATP-Dependent Proteases MeSH
• Peptide Hydrolases MeSH
• Protein Isoforms MeSH
• Electron Transport Complex I MeSH
• Electron Transport Complex IV MeSH
• Saccharomyces cerevisiae Proteins MeSH
• YME1 protein, S cerevisiae MeSH Browser
• YME1L1 protein, human MeSH Browser