2D electron microscopic images of αIIbβ3 embedded in a phospholipid bilayer nanodisc. (A) αIIb contains 7 domains and β3 contains 10 domains. The heterodimeric structure is maintained by the association of the αIIb β-propeller domain and the β3 β I domain, both of which contribute to the ligand-binding region, and the association of the αIIb and β3 TM domains. (B) Representative classified averages of αIIbβ3 nanodisc EM images obtained at 120 kV showing different views. (C) The averaged classes of αIIbβ3 nanodisc images at 200 kV. The circular-to-oblong structures between the β-propeller domain and the nanodisc are indicated by black arrows in the first image. (D) A representative class average of mouse mAb 10E5 (IgG). (E) Representative averaged images of the binding of mAb 10E5 (directed at the αIIb cap domain), mAb 7E3 (directed at β3 βI domain), and mAb 7H2 (directed at the β3 PSI domain). (F) The locations of the αIIb cap domain and the β3 PSI and βI domains (white arrows) according to the 3D map in Figure 2A. Note the correspondence between the mAb data and the 3D map data. Scale bars in panels B-F = 10 nm.