Loop recognition and copper-mediated disulfide reduction underpin metal site assembly of CuA in human cytochrome oxidase

Proc Natl Acad Sci U S A. 2015 Sep 22;112(38):11771-6. doi: 10.1073/pnas.1505056112. Epub 2015 Sep 8.


Maturation of cytochrome oxidases is a complex process requiring assembly of several subunits and adequate uptake of the metal cofactors. Two orthologous Sco proteins (Sco1 and Sco2) are essential for the correct assembly of the dicopper CuA site in the human oxidase, but their function is not fully understood. Here, we report an in vitro biochemical study that shows that Sco1 is a metallochaperone that selectively transfers Cu(I) ions based on loop recognition, whereas Sco2 is a copper-dependent thiol reductase of the cysteine ligands in the oxidase. Copper binding to Sco2 is essential to elicit its redox function and as a guardian of the reduced state of its own cysteine residues in the oxidizing environment of the mitochondrial intermembrane space (IMS). These results provide a detailed molecular mechanism for CuA assembly, suggesting that copper and redox homeostasis are intimately linked in the mitochondrion.

Keywords: CuA site; Sco proteins; cytochrome oxidase; metal site assembly; metallochaperones.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Carrier Proteins / chemistry
  • Carrier Proteins / metabolism
  • Copper / metabolism*
  • Disulfides / metabolism*
  • Electron Transport
  • Electron Transport Complex IV / chemistry*
  • Electron Transport Complex IV / metabolism*
  • Humans
  • Membrane Proteins / chemistry
  • Membrane Proteins / metabolism
  • Mitochondrial Proteins / chemistry
  • Mitochondrial Proteins / metabolism
  • Models, Molecular
  • Molecular Chaperones
  • Molecular Sequence Data
  • Oxidation-Reduction
  • Protein Engineering
  • Protein Structure, Secondary
  • Protein Subunits / chemistry
  • Proton Magnetic Resonance Spectroscopy
  • Solubility
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization


  • Carrier Proteins
  • Disulfides
  • Membrane Proteins
  • Mitochondrial Proteins
  • Molecular Chaperones
  • Protein Subunits
  • SCO1 protein, human
  • SCO2 protein, human
  • Copper
  • Electron Transport Complex IV