Analysis of αIIbβ3 alone and in complex with R6H8 Fab, revealing a ligand-mimetic mode of binding. (A-D) Cryo-EM analysis of αIIbβ3 by itself (A-B) and in complex with R6H8 Fab (C-D). Shown are the density maps colored by domains (panels A,C) and models in ribbon representation (panels B,D). (E) Enlarged view of the region marked in panel D showing the interaction interface between the αIIbβ3 headpiece and the R6H8 Fab. (F) Zoomed-in views of the regions marked and labeled (1) to (3) in panel E. Residues involved in the interactions are shown as sticks. The synergistic metal ion binding site and MIDAS cations are shown as yellow and gold spheres, respectively. Charge interactions are indicated by red dashed lines and hydrogen bonds by black dashed lines.