β₃integrin extension at the I-EGF1/I-EGF2 junction. (A) Structural superposition of the cβ₃-E2 I-EGF1-2 domains on the I-EGF1 (upper) or the I-EGF2 (lower) domain of the bent native β₃ structure (PDB 4G1M). (B-D) The 3 structures are shown separately after being superimposed on the I-EGF2 domains. The bent (B), intermediate (C), and extended (D) forms are shown in cyan, green, and red, respectively. Disulfide bonds are sticks. Residues of interest are shown as Cα spheres. The 8 cysteines of the I-EGF2 domain are numbered. (E) Structural superposition on the I-EGF2 of the bent (PDB code 4NEH), intermediate (PDB 2V26), and extended (PDB 2V28) I-EGF1-2 domains of β₂ integrin. (F) Structural superposition on I-EGF2 of the extended I-EGF1-2 domains of β₃ (red) and β₂ (green) integrins. (G-H) Structural comparison of the extended β₃ I-EGF1-2 (PDB 6BXB) with the β₃ I-EGF2-3 (G; PDB 3FCS) or I-EGF3-4 (H; PDB 3FCS) domains. The I-EGF3 or I-EGF4 domain was superimposed onto the I-EGF2 domain.