Adenosine 5'-triphosphate-dependent vitamin D sterol binding to heat shock protein-70 chaperones

Rene Chun, Mercedes A Gacad, Martin Hewison, John S Adams

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


Chaperone proteins in the heat shock protein-70 family possess endogenous ATP binding and ATPase activity and interact with intracellular protein substrates in an ATP-dependent manner; the hydrolysis of ATP to ADP results in an increase in the affinity of the chaperone for protein substrates. Heat shock protein-70s can also specifically interact with 25-hydroxylated vitamin D metabolites. Using constitutively expressed heat shock protein-70 (hsc70) as chaperone, here we demonstrate that vitamin D metabolite binding to hsc70 is also ATP dependent. Transient overexpression of an hsc70-green fluorescent protein chimeric construct in primate kidney cells resulted in a 6-fold increase in specific, extractable 25-hydroxyvitamin D(3) binding. When ATPase capability of hsc70 was disabled, this increase was completely blocked. In solution, the binding of 25-hydroxylated vitamin D metabolites to hsc70 was significantly increased (P < 0.01) in the presence of ATP and a nonmetabolizable ATP analog. The ATP-directed increase in specific binding resulted from an increase in the abundance of relatively high-affinity hormone-binding sites (K(d), approximately 0.24 nM). These results suggest that ATP hydrolysis to ADP would favor the release of vitamin D from a donor hsc70 molecule at a time when an hsc70-bound acceptor protein substrate is anchored to the chaperone with relative avidity. We theorize that the endogenous ATPase activity of hsc70 promotes the transfer of vitamin D sterols to other intracellular vitamin D binding proteins, such as the vitamin D receptor and vitamin D hydroxylases, to which hsc70 is known to bind.

Original languageEnglish
Pages (from-to)5540-4
Number of pages5
Issue number12
Publication statusPublished - Dec 2005


  • Adenosine Triphosphate
  • Animals
  • Cell Line
  • Green Fluorescent Proteins
  • HSP70 Heat-Shock Proteins
  • Ligands
  • Molecular Chaperones
  • Primates
  • Recombinant Fusion Proteins
  • Sterols
  • Vitamin D


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