Structure of αIIbβ3. An early model of the αIIbβ3 complex (top left) illustrates a number of relevant functional and structural features, including major ligand contact sites (within the yellow rectangle), and the calcium binding region and interchain and intrachain disulfide bonds in αIIb (GPIIb; blue). The β3 subunit is shown in red with its 5 cysteine-rich regions, 1 at the N-terminus and 4 in the stalk, ligand contact sites (yellow rectangle), and 2 chymotrypsin-sensitive cleavage sites (jagged line) that remove the ligand-binding segment, now termed A. Domains visible in the crystal structure of the closely related αVβ3 (top right and bottom panels) are shown in detail and discussed in the text. The PSI domain (bottom left) is depicted schematically because its structure has not been determined. Adapted from Xiong et al²⁰  and Newman139 with permission.