title: Structures of the platelet calcium- and integrin-binding protein and the alphaIIb-integrin cytoplasmic domain suggest a mechanism for calcium-regulated recognition; homology modelling and NMR studies.
abstract: Calcium- and integrin-binding protein (CIB) binds to the 20-residue alphaIIb cytoplasmic domain of platelet alphaIIbbeta3 integrin. Amino acid sequence similarities with calmodulin (CaM) and calcineurin B (CnB) allowed the construction of homology-based models of calcium-saturated CIB as well as apo-CIB. In addition, the solution structure of the alphaIIb cytoplasmic domain in 45% aqueous trifluoroethanol was solved by conventional two-dimensional NMR methods. The models indicate that the N-terminal domain of CIB possesses a number of positively charged residues in its binding site that could interact with the acidic carboxy-terminal LEEDDEEGE sequence of alphaIIb. The C-terminal domain of CIB seems well-suited to bind the sequence WKVGFFKR, which forms a well-structured alpha helix; this is analogous to calmodulin and calcineurin B, which also bind alpha helices. Similarities between the C-terminal domains of CIB and calmodulin suggest that binding of CIB to the cytoplasmic domain of alphaIIb may be affected by fluctuations in the intracellular calcium concentration.
authors.affiliation: Department of Biological Sciences, University of Calgary, Alberta, Canada.
authors.forename: P M
authors.initials: PM
authors.lastname: Hwang
authors.forename: H J
authors.initials: HJ
authors.lastname: Vogel
mesh_terms: D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000737:chemistry; D019703:Calcineurin / Q000737:chemistry; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins; D002147:Calmodulin / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: C109198:CIB1 protein, human; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D002352:Carrier Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019703:Calcineurin; D002118:Calcium