The deletion of GPIbα C-terminal 10 residues reduces various agonist-induced platelet aggregation, α_IIbβ₃ activation, granule secretion, and PS exposure. (A) Schematic depicting the construction of 10aa^−/− mice. (B) Western blot analysis of GPIbα in WT and 10aa^−/− platelet lysates with anti-GPIbα N- and C-terminal antibodies. Protein concentrations have been adjusted to the same level in platelet lysates. Blots are representative of 6 mice per genotype. The lack of C-terminal amino acids was also verified by mass spectrometry (data not shown). (C) Representative agonist-induced platelet aggregation traces in washed WT and 10aa^−/− platelets (upper) and quantification of maximal aggregation rate (lower) (n = 5 independent experiments). (D) Agonist-induced JON/A binding, (E) P-selectin exposure, (F) ATP release, and (G) PS externalization in washed WT and 10aa^−/− platelets (n = 5 mice per genotype). Two-tailed Student t test in panels C,F. Two-way ANOVA followed by Bonferroni post hoc test in panels D-E,G. Data are shown as mean ± SEM for panels C-G. ∗P < .05, ∗∗P < .01, and ∗∗∗P < .001.