Interactions in the head domain of αIIbβ3 between aromatic residues from blades 2 and 3 of the β-propeller of αIIb (Trp110 and Phe171) and Arg261 of β3. (A) The β-propeller domain of αIIb is presented in black ribbons and the βA domain of β3 is presented in light gray coil derived from PDB 1TXV. β3-Arg261, αIIb-Trp110, and αIIb-Phe171 are depicted by space-filled atoms. (B) Effect of αIIb-Trp110Ala and -Phe171Ala substitutions on αIIbβ3 surface expression and ligand binding. Flow cytometric analysis of αIIbβ3 surface expression in BHK cells expressing WT β3 and mutated or WT αIIb was preformed using monoclonal antibody against αIIbβ3 (P2) and monoclonal antibody against αIIb (CA3). Fibrinogen (Fb) binding was measured with anti–human fibrinogen antibody after activation by PT25-2 activating antibody. All antibody bindings are presented as mean percentage of WT MFI ± SD (at least 3 different transfections). *P < .05. (C) Intracellular maturation of αIIb was measured by immunoblotting of reduced cell lysates in Tris-acetate 3%-8% gels with monoclonal antibody specific to αIIb (SZ22). The proportion of mature αIIb of total αIIb (mature and pro-αIIb) in percentage was calculated by measuring band intensity using EZQuant densitometry program. Total protein loading was measured by polyclonal anti-calnexin antibody.