Extended structure of β₃integrin. (A) Two different views of the intermediate (green) and extended (red) cβ₃-E2 structures superimposed on the I-EGF2 domain of the bent (cyan) native β₃ structure (PDB 4G1M). (B) Intermediated (half-extended) conformation of α_IIbβ₃. The structure was built based on the intermediated conformation of I-EGF1-2 and shown in 2 views. The negative staining EM images shown are full-length α_IIbβ₃ (i),¹¹  ectodomain of α_Vβ₃ (ii),⁷  ectodomain of α_IIbβ₃ (iii),⁵  and full-length α_IIbβ₃ (iv).¹¹  The images were not shown in the same scale. (C-D) Modeled extended β₃ structure with closed (C) or open (D) headpiece. The model was generated by the superimposition of the extended cβ₃-E2 structure onto the I-EGF2 domain of the native β₃ structure first and then superimposition of the closed or open β₃ headpiece structure onto the hybrid domain of the cβ₃-E2 structure. (E-F) Overlay of the extended β₃ structure with the EM image of extended α_Vβ₃⁷  with closed headpiece (E) or extended α_IIbβ₃ with open headpiece¹¹  (F). (G) α_IIb thigh/calf-1 interface at the bent conformation (PDB 3FCS). Interfacial residues are shown as sticks with green and cyan carbons for thigh and calf-1 domains, respectively. Hydrogen bonds are dashed in magenta. Disulfide bonds are yellow sticks. Panels Bi, Biv, and F reprinted from Eng et al¹¹  with permission; panels Bii and E are reprinted from Takagi et al⁷  with permission; and panel Biii is reprinted from Zhu et al⁵  with permission.