Ribbon diagram of the structure of the unliganded extracellular α_Vβ₃. The protein is bent at a flexible region (the genu, arrow; A). When extended at the genu,¹⁶  the structure assumes the more familiar shape seen previously by electron microscopy (B). The 12 domains are labeled. The PSI, EGF1, and EGF2 domains are not visible (indicated in gray); the tracing shown for PSI is approximate and the translated EGF3 and EGF4 domains have been used to show the approximate location of EGF1 and EGF2. The 4 metal ions (orange spheres) at the bottom of the propeller, the metal ion at the genu (orange), and the ADMIDAS ion (magenta) are shown. The dotted line in calf-2 represents the disordered loop containing the proteolytic cleavage site. A short dotted line also connects PSI and the hybrid domains, visible in panel B. The “n” and “c” indicate the amino and carboxyl terminus, respectively. Reprinted from Arnaout et al⁵⁸  with permission.