Identification of residues of functional importance within the central turn motifs present in the cytoplasmic tails of integrin αIIb and αV subunits

IntroductionPrevious studies demonstrated that cell-permeable αIIb cytoplasmic peptides can modulate the activation of αIIbβ3. An integrin activation motif was mapped to its membrane proximal region and a double proline mutant peptide and receptor indicated that its central turn motif had inhibitory capacity. However, the residues critical for inhibition of αIIbβ3 activation were not identified. Using central turn peptides derived from αIIb and αV, residues critical for suppression of integrin activation were identified and the importance of these residues in protein–protein interactions was assessed.Materials and methodsCell-permeable peptides were used to determine the capacity of the central turn peptides to suppress αIIbβ3 and αVβ3 activation. Far Western analysis was used to characterize the capacity of the peptides to interact with CIB1 and surface plasmon resonance was used to characterize the binding of an antibody to the cytoplasmic tails of αIIb and αV.Results and conclusionsThe central turn peptide from αV, αV(993–1001), has full inhibitory capacity while that derived from αIIb requires additional residues located adjacent to αIIb(995–1003). Within these two sequences there is a switch in the position of an asparaginine and leucine residue for a valine and glutamine (αIIb, RNRPPLEED; αV, RVRPPQEEQ). This switch had a dramatic effect on their inhibitory capacity and on protein–protein interactions. The two arginine and glutamic residues, juxtapositioned at identical locations in both subunits, appeared to be important in specifying the orientation by which proteins can dock to this region in αIIb and αV.