The CO dehydrogenase accessory protein CooT is a novel nickel-binding protein

Metallomics. 2017 May 24;9(5):575-583. doi: 10.1039/c7mt00063d.


In Rhodospirillum rubrum, maturation of Carbon Monoxide Dehydrogenase (CODH) requires three accessory proteins, CooC, CooT and CooJ, dedicated to nickel insertion into the active site, which is constituted by a distorted [NiFe3S4] cubane coordinated with a mononuclear Fe site. CooC is an ATPase proposed to provide the energy required for the maturation process, while CooJ is described as a metallochaperone with 16 histidines and 2 cysteines at the C-terminus, likely involved in metal binding and/or storage. Prior to the present study, no information was available on CooT at the molecular level. Here, the X-ray structure of RrCooT was obtained, which revealed that this protein is a homodimer featuring a fold that resembles an Sm-like domain, suggesting a role in RNA metabolism that was however not supported by experimental observations. Biochemical and biophysical evidence based on circular dichroism spectroscopy, light scattering, isothermal titration calorimetry and site-directed mutagenesis showed that RrCooT specifically binds a single Ni(ii) per dimer, with a dissociation constant of 9 nM, through the pair of Cys2, highly conserved residues, located at the dimer interface. Despite its role in the activation of RrCODH in vivo, CooT was thought to be a unique protein, found only in R. rubrum, with an unclear function. In this study, we extended the biological impact of CooT, establishing that this protein is a member of a novel Ni(ii)-binding protein family with 111 homologues, linked to anaerobic metabolism in bacteria and archaea, and in most cases to the presence of CODH.

MeSH terms

  • Aldehyde Oxidoreductases / chemistry
  • Aldehyde Oxidoreductases / metabolism
  • Amino Acid Sequence
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism*
  • Carrier Proteins / chemistry
  • Carrier Proteins / metabolism*
  • Crystallography, X-Ray
  • Models, Molecular
  • Multienzyme Complexes / chemistry
  • Multienzyme Complexes / metabolism
  • Nickel / metabolism*
  • Protein Binding
  • Protein Conformation, beta-Strand
  • Protein Multimerization
  • Rhodospirillum rubrum / chemistry
  • Rhodospirillum rubrum / metabolism*


  • Bacterial Proteins
  • Carrier Proteins
  • CooT protein, Rhodospirillum rubrum
  • Multienzyme Complexes
  • Nickel
  • Aldehyde Oxidoreductases
  • carbon monoxide dehydrogenase