Structure and mechanistic insights into novel iron-mediated moonlighting functions of human J-protein cochaperone, Dph4

J Biol Chem. 2012 Apr 13;287(16):13194-205. doi: 10.1074/jbc.M112.339655. Epub 2012 Feb 24.


J-proteins are obligate cochaperones of Hsp70s and stimulate their ATPase activity via the J-domain. Although the functions of J-proteins have been well understood in the context of Hsp70s, their additional co-evolved "physiological functions" are still elusive. We report here the solution structure and mechanism of novel iron-mediated functional roles of human Dph4, a type III J-protein playing a vital role in diphthamide biosynthesis and normal development. The NMR structure of Dph4 reveals two domains: a conserved J-domain and a CSL-domain connected via a flexible linker-helix. The linker-helix modulates the conformational flexibility between the two domains, regulating thereby the protein function. Dph4 exhibits a unique ability to bind iron in tetrahedral coordination geometry through cysteines of its CSL-domain. The oxidized Fe-Dph4 shows characteristic UV-visible and electron paramagnetic resonance spectral properties similar to rubredoxins. Iron-bound Dph4 (Fe-Dph4) also undergoes oligomerization, thus potentially functioning as a transient "iron storage protein," thereby regulating the intracellular iron homeostasis. Remarkably, Fe-Dph4 exhibits vital redox and electron carrier activity, which is critical for important metabolic reactions, including diphthamide biosynthesis. Further, we observed that Fe-Dph4 is conformationally better poised to perform Hsp70-dependent functions, thus underlining the significance of iron binding in Dph4. Yeast Jjj3, a functional ortholog of human Dph4 also shows a similar iron-binding property, indicating the conserved nature of iron sequestration across species. Taken together, our findings provide invaluable evidence in favor of additional co-evolved specialized functions of J-proteins, previously not well appreciated.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / chemistry
  • Adenosine Triphosphatases / metabolism
  • Diphtheria Toxin / metabolism
  • Evolution, Molecular*
  • HSP40 Heat-Shock Proteins / chemistry*
  • HSP40 Heat-Shock Proteins / metabolism*
  • HSP70 Heat-Shock Proteins / metabolism
  • Humans
  • Iron / metabolism*
  • Molecular Chaperones / chemistry*
  • Molecular Chaperones / metabolism*
  • Nuclear Magnetic Resonance, Biomolecular
  • Oxidation-Reduction
  • Protein Structure, Tertiary
  • Structure-Activity Relationship
  • Yeasts / metabolism
  • Zinc Fingers / physiology


  • DNAJC24 protein, human
  • Diphtheria Toxin
  • HSP40 Heat-Shock Proteins
  • HSP70 Heat-Shock Proteins
  • Molecular Chaperones
  • Iron
  • Adenosine Triphosphatases

Associated data

  • PDB/2L6L