Progression of αIIbβ3 conformations during biogenesis. (A) The conformations of free pro-αIIb, free β3, and pro-αIIbβ3 are unknown. The conformation of mature, bent, unactivated αIIbβ3 and the proposed extended structure of activated, ligand-bound αIIbβ3 are modeled after the crystal structures of αVβ3 and the αIIbβ3 headpiece, respectively. The domains of αIIb and β3 are indicated.^12,15  (B) Immunoprecipitation with αIIbβ3 complex-specific mAbs 10E5 and 7E3 following pulse-chase labeling demonstrates that both antibodies recognize the pro-αIIbβ3 complex in addition to the mature αIIbβ3 complex. The figure on the left indicates the locations of the 10E5 and 7E3 epitopes on models of the extended and bent forms of αIIbβ3. This figure has been adapted from its original published form with the permission of the journal Clinical Pharmacology & Therapeutics.