title: Identification of residues of functional importance within the central turn motifs present in the cytoplasmic tails of integrin alphaIIb and alphaV subunits.
abstract: BACKGROUND
  Previous studies demonstrated that cell-permeable alphaIIb cytoplasmic peptides can modulate the activation of alphaIIbbeta3. 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 alphaIIbbeta3 activation were not identified. Using central turn peptides derived from alphaIIb and alphaV, residues critical for suppression of integrin activation were identified and the importance of these residues in protein-protein interactions was assessed.
  
  
  METHODS
  Cell-permeable peptides were used to determine the capacity of the central turn peptides to suppress alphaIIbbeta3 and alphaVbeta3 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 alphaIIb and alphaV.
  
  
  CONCLUSIONS
  The central turn peptide from alphaV, alphaV(993-1001), has full inhibitory capacity while that derived from alphaIIb requires additional residues located adjacent to alphaIIb(995-1003). Within these two sequences there is a switch in the position of an asparaginine and leucine residue for a valine and glutamine (alphaIIb, RNRPPLEED; alphaV, 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 alphaIIb and alphaV.
authors.affiliation: Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5. thomas.haas@usask.ca
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Haas
authors.forename: Aliakbar
authors.initials: A
authors.lastname: Taherian
authors.forename: Tangyne
authors.initials: T
authors.lastname: Berry
authors.forename: Xinfeng
authors.initials: X
authors.lastname: Ma
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry; D003593:Cytoplasm / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D039564:Integrin alphaV / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D040201:Platelet Membrane Glycoprotein IIb / Q000737:chemistry*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020349:Surface Plasmon Resonance
chemical_list: D039564:Integrin alphaV; D008024:Ligands; D010455:Peptides; D040201:Platelet Membrane Glycoprotein IIb; D001120:Arginine