A conserved arginine at the hybrid-PSI interface. (A-B) The hybrid-PSI interface of bent (A) and extended (B) β₃. Disulfide bonds are yellow sticks. Hydrogen bonds are dashed in magenta. (C) Sequence alignment of the hybrid domain A’B loop. (D-H) PAC-1, ICAM-1, fibronectin (Fn), or 9EG7 binding of the β₃-R93 (D-E), β₂-R87 (F), or β₁-R104 (G-H) mutations coexpressed with α_IIb (D), α_V (E), α_L (F), or α₅ (G-H) integrin in HEK293FT cells. The binding was performed in the presence of 1 mM of Ca²⁺/Mg²⁺ (Ca/Mg) or 0.2 mM of Ca²⁺ plus 2 mM Mn²⁺ (Ca/Mn) and is presented as mean fluorescence intensity (MFI) normalized to integrin expression. One representative result is shown. WT, wild type.