Calcium-binding domains in the α-subunit of integrins contain a central loop structure. To examine the importance of the loop structure, a series of αIIb mutants containing changes to the calcium-liganding amino acids have been constructed. Significantly, none of the mutant αIIbβ3 complexes was detected on the surface of transfected cells, but mutant pro-αIIb was detected in cell lysates in complex with β3. To study the importance of the regions flanking the second calcium-binding domain for ligand-binding and ligand-binding specificity, three αIIb/α5 chimaeras containing α5 sequences flanking or flanking and including the second calcium-binding domain were constructed. The chimaera containing both α5-flanking regions was not expressed on the cell surface, but FR1 and FR2, substituting either the first or second flanking region, were expressed. FR1β3-transfected cells lost the ability to adhere to fibrinogen and to support aggregation and had minimal fibrinogen-binding ability. The heterodimer complex was less stable than the wild-type. FR2β3-transfected cells adhered to fibrinogen and bound soluble fibrinogen with higher affinity when compared with wild-type. In addition, the heterodimer complex was more stable than wild-type. These results indicate that the conformation of the second calcium-binding domain is critical for maturation of the αIIbβ3 complex and expression on the cell surface and that the surrounding sequences are critical for αIIbβ3 function.
Mutations in and near the second calcium-binding domain of integrin alphaIIb affect the structure and function of integrin alphaIIbbeta3
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Susan GIDWITZ, Brenda TEMPLE, Gilbert C. WHITE; Mutations in and near the second calcium-binding domain of integrin alphaIIb affect the structure and function of integrin alphaIIbbeta3. Biochem J 15 April 2004; 379 (2): 449–459. doi: https://doi.org/10.1042/bj20030615
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