A divalent metal ion binding site in the kinase insert domain of the alpha-platelet-derived growth factor receptor regulates its association with SH2 domains

Biochemistry. 1995 Feb 21;34(7):2095-106. doi: 10.1021/bi00007a002.


To investigate the effects of metal ion binding to the alpha-PDGFR kinase insert domain, a PCR product representing amino acid residues 691-795 (104 amino acids) was bacterially expressed and purified. Secondary structure prediction and circular dichroism spectroscopy indicated this domain to be a mixed alpha + beta protein with a large coil/turn contribution. This 16 kDa, soluble, nonphosphorylated domain bound to 45Ca2+ and 65Zn2+ through a common shared site. Of the unlabeled divalent and trivalent metal ions tested, Ho3+ = Zn2+ > Ni2+ > Ca2+ = Mn2+ > Mg2+, Ba2+ in competing for 45Ca2+ binding to this domain. In the presence of Ca2+ ions, the conformation of the KI domain changed significantly, and this changed conformation was resistant to subtilisin proteolysis. However, in the presence of Zn2+ ions, the conformation of the KI domain changed only slightly. Nevertheless, Zn2+ ions were more effective in rendering the KI domain resistant to proteolysis as compared to that shown by Ca2+ ions. In vitro binding studies using purified baculovirus-expressed alpha-PDGFR showed a marked increase in binding the p85 N-SH2 domain in the presence of Ca2+ or Zn2+ ions (KD = 0.5 microM), suggesting that metal ion binding enhances association of the p85 N-SH2 domain with the receptor. To confirm this, association of the alpha-PDGFR with the p85 N-SH2 domain was tested in the presence of the KI domain. The nonphosphorylated KI domain was effective in competing with the alpha-PDGFR for the binding of the p85 N-SH2 domain. This effect was more pronounced in the presence of Ca2+ ions. Microinjection of this domain into Xenopus oocytes delayed maturation in the presence of insulin but not progesterone. This suggests that the KI domain has a correctly folded three-dimensional structure compatible with biological activity. Together these findings indicate that the recombinant alpha-PDGFR KI domain binds the p85 N-SH2 domain and this binding is modulated by the presence of a novel divalent metal ion binding site within its structure.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Binding, Competitive
  • Calcium / metabolism*
  • Cations, Divalent
  • Circular Dichroism
  • Humans
  • In Vitro Techniques
  • Molecular Sequence Data
  • Oncogene Proteins, Viral / chemistry
  • Oocytes
  • Phosphatidylinositol 3-Kinases
  • Phosphatidylinositols / metabolism
  • Phosphotransferases (Alcohol Group Acceptor) / metabolism*
  • Protein Binding
  • Protein Conformation
  • Receptor Protein-Tyrosine Kinases / metabolism*
  • Receptors, Platelet-Derived Growth Factor / metabolism*
  • Recombinant Proteins
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Signal Transduction
  • Subtilisins / pharmacology
  • Xenopus laevis
  • Zinc / metabolism*


  • Cations, Divalent
  • Oncogene Proteins, Viral
  • Phosphatidylinositols
  • Recombinant Proteins
  • Phosphatidylinositol 3-Kinases
  • Phosphotransferases (Alcohol Group Acceptor)
  • Receptor Protein-Tyrosine Kinases
  • Receptors, Platelet-Derived Growth Factor
  • Subtilisins
  • Zinc
  • Calcium