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Molecular basis of CIB binding to the integrin alpha IIb cytoplasmic domain

William T Barry1, Christel Boudignon-Proudhon, David D Shock

  • 1Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.

The Journal of Biological Chemistry
|May 23, 2002
PubMed

Insights

Specific hydrophobic residues in the C-terminus of CIB protein are crucial for binding to the alpha(IIb) cytoplasmic tail of platelet integrin alpha(IIb)beta(3), revealing key interaction sites.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Integrin adhesion receptors are regulated by proteins binding to their cytoplasmic domains.
  • CIB (Calcium and Integrin Binding Protein) is a 22-kDa EF-hand protein that binds to the alpha(IIb) cytoplasmic tail of platelet integrin alpha(IIb)beta(3).

Purpose of the Study:

  • To delineate the specific interaction regions between CIB and the alpha(IIb) cytoplasmic tail.
  • To identify the key residues in CIB and alpha(IIb) responsible for their binding interaction.

Main Methods:

  • Peptide binding assays using intrinsic tryptophan fluorescence to measure CIB interaction with alpha(IIb) cytoplasmic tail peptides.
  • Homology modeling of CIB based on calcineurin B and recoverin structures.
  • Site-directed mutagenesis of CIB, followed by circular dichroism to assess secondary structure and binding assays to evaluate alpha(IIb) interaction.

Main Results:

  • A 15-amino acid, membrane-proximal region of alpha(IIb) contains the CIB-binding site, characterized by hydrophobic residues.
  • A conserved hydrophobic pocket in the C-terminal EF-hand motifs of CIB is identified as a potential integrin-binding site.
  • Mutagenesis of specific hydrophobic residues in the C-terminus of CIB abolished binding to alpha(IIb), while N-terminal mutations retained binding.

Conclusions:

  • Specific hydrophobic residues in the C-terminus of CIB are essential for its binding to the alpha(IIb) cytoplasmic tail.
  • The identified interaction regions provide a basis for further investigation into the functional interplay between CIB and integrins.

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