Effects of β3 cytoplasmic tail mutations on β3/protein interactions. (A) Amino acid sequences of the β3^+/+, β3ΔRGT, and β3/β1(EGK) cytoplasmic tails used in these studies. Pull-down of c-Src, kindlin-2, or talin from (B) immortalized mouse lung endothelial cell lysate (as a convenient source of talin and kindlin-2) or (C) human platelet lysate (as a convenient source of talin and c-Src) by recombinant β3^+/+ or mutant β3 cytoplasmic domain model proteins. The αIIb cytoplasmic domain was used as a negative control. Bound talin, kindlin-2, and c-Src were detected by immunoblotting. Loading of pull-down beads with recombinant cytoplasmic domains was monitored by staining with Coomassie brilliant blue. (Left panel) Representative images of pull-downs; (right panel) quantification of binding of kindlin-2 (B) or c-Src (C). Binding of kindlin-2 or c-Src to αIIb or mutant β3 tails was expressed relative to their binding to the β3^+/+ tail, which was arbitrarily taken as 1.0. Data represent means ± standard error of the mean (SEM) of 3 independent experiments. **P < .01; *P < .05; NS, not significant (paired Student t test).