Cryo-EM structure of the αIIbβ3 headpiece in complex with the PT25-2 Fab. (A) Density map of the αIIbβ3–PT25-2 Fab complex at 3.3-Å resolution, segmented and colored according to the individual polypeptide chains. Asterisk indicates the ligand-binding site. (B) Atomic model of the αIIbβ3–PT25-2 Fab complex colored as in panel A. VH, variable domain of the heavy chain; CH1, first constant domain of the heavy chain; VL, variable domain of the light chain; CL, constant domain of the light chain. (C) Interaction surfaces of αIIb (i) and the PT25-2 Fab (ii). Side chains of residues that are within 4 Å from a side chain of the interacting protein are shown in stick representation.