The arginine methyltransferase NDUFAF7 is essential for complex I assembly and early vertebrate embryogenesis

Hum Mol Genet. 2014 Oct 1;23(19):5159-70. doi: 10.1093/hmg/ddu239. Epub 2014 May 16.


Complex I of the mitochondrial respiratory chain is a large multisubunit enzyme that assembles from nuclear and mtDNA-encoded components. Several complex I assembly factors have been identified, but their precise functions are not well understood. Here, we have investigated the function of one of these, NDUFAF7, a soluble matrix protein comprised of a DUF185 domain that harbors a methyltransferase motif. Knockdown of NDUFAF7 by siRNA in human fibroblasts produced a specific complex I assembly defect, as did morpholino-mediated knockdown of the zebrafish ortholog. Germline disruption of the murine ortholog was an early embryonic lethal. The complex I assembly defect was characterized by rapid, AFG3L2-dependent, turnover of newly synthesized ND1, the subunit that seeds the assembly pathway, and by decreased steady-state levels of several other structural subunits including NDUFS2, NDUFS1 and NDUFA9. Expression of an NDUFAF7 mutant (G124V), predicted to disrupt methyltransferase activity, impaired complex I assembly, suggesting an assembly factor or structural subunit as a substrate for methylation. To identify the NDUFAF7 substrate, we used an anti-ND1 antibody to immunoprecipitate complex I and its associated assembly factors, followed by mass spectrometry to detect posttranslational protein modifications. Analysis of an NDUFAF7 methyltransferase mutant showed a 10-fold reduction in an NDUFS2 peptide containing dimethylated Arg85, but a 5-fold reduction in three other NDUFS2 peptides. These results show that NDUFAF7 functions to methylate NDUFS2 after it assembles into a complex I, stabilizing an early intermediate in the assembly pathway, and that this function is essential for normal vertebrate development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Animals
  • CDPdiacylglycerol-Serine O-Phosphatidyltransferase / genetics
  • Cell Line
  • Electron Transport Complex I / metabolism*
  • Embryonic Development / genetics*
  • Fibroblasts
  • Gene Knockdown Techniques
  • Genes, Lethal
  • Humans
  • Mice
  • Mice, Knockout
  • Mitochondria / metabolism
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism
  • NADH Dehydrogenase / chemistry
  • NADH Dehydrogenase / genetics*
  • NADH Dehydrogenase / metabolism
  • Phenotype
  • Protein Interaction Domains and Motifs
  • Proteolysis
  • RNA Interference
  • Substrate Specificity
  • Vertebrates
  • Zebrafish


  • Mitochondrial Proteins
  • NDUFAF7 protein, human
  • NADH Dehydrogenase
  • CDPdiacylglycerol-Serine O-Phosphatidyltransferase
  • Electron Transport Complex I