title: The interaction between calcium- and integrin-binding protein 1 and the alphaIIb integrin cytoplasmic domain involves a novel C-terminal displacement mechanism.
abstract: Calcium- and integrin-binding protein 1 (CIB1) regulates platelet aggregation in hemostasis through a specific interaction with the alphaIIb cytoplasmic domain of platelet integrin alphaIIbbeta3. In this work we report the structural characteristics of CIB1 in solution and the mechanistic details of its interaction with a synthetic peptide derived from the alphaIIb cytoplasmic domain. NMR spectroscopy experiments using perdeuterated CIB1 together with heteronuclear nuclear Overhauser effect experiments have revealed a well folded alpha-helical structure for both the ligand-free and alphaIIb-bound forms of the protein. Residual dipolar coupling experiments have shown that the N and C domains of CIB1 are positioned side by side, and chemical shift perturbation mapping has identified the alphaIIb-binding site as a hydrophobic channel spanning the entire C domain and part of the N domain. Data obtained with a truncated version of CIB1 suggest that the extreme C-terminal end of the protein weakly interacts with this channel in the absence of a biological target, but it is displaced by the alphaIIb cytoplasmic domain, suggesting a novel mechanism to increase binding specificity.
authors.affiliation: Structural Biology Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Yamniuk
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ishida
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Vogel
mesh_terms: D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010974:Platelet Aggregation / Q000502:physiology; D040201:Platelet Membrane Glycoprotein IIb / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism
chemical_list: C109198:CIB1 protein, human; D002135:Calcium-Binding Proteins; D010455:Peptides; D040201:Platelet Membrane Glycoprotein IIb; D021122:Protein Subunits