Hybrid domain swing out. (A–D) One integrin molecule is shown as a Cα trace, with different colors for each domain. The hybrid domain (red) and PSI and I-EGF-1 domains (yellow) are shown as thicker traces for emphasis. Other integrin molecules and all Fabs in the crystal lattice are shown as white, semitransparent, solvent accessible surfaces. The label hybrid is placed in identical positions in A–D. (A) Molecule 2 before soaking (3T3P closed structure). (B) Molecule 1 after soaking with 10 mM RGD and Mn/Ca. (C) Molecule 2 after soaking with 10 mM RGD and Mn/Ca. Composite omit simulated-annealing electron density contoured at 0.5 σ around the hybrid domain is shown as purple mesh. PSI and I-EGF-1 domains are missing in density, and superposition on the hybrid domain is used to show their approximate location in the lattice. (D) The native open headpiece (Protein Data Bank [PDB] accession no. 2VDR) superimposed based on the β-propeller and βI domains in C and shown in the same lattice as in C. Severe clashes are evident. (E) Superposition of α_IIbβ₃ headpieces. Similar regions in gray and colored shape-shifting portions in cartoon; metal ions are shown as spheres, and RGD is shown in stick. Structures are molecule 2 after soaking with 10 mM RGD and Mn/Ca (red), native closed (PDB accession no. 3T3P; blue), and native open (PDB accession no. 2VDR; green).