H/D exchange difference map of human PAR4 in apo and thrombin-activated states. The percent deuteration of the thrombin-activated state was subtracted from the percent deuteration of the apo state. The PAR4 homology model was color-coded on the basis of the difference in percent deuteration between the 2 states (Δ % deuteration [apo-activated]): dark blue for –9% to <−7%, light blue for −7% to <−5%, cyan for –5% to <−3%, cadet blue for –3% to <−1%, green for –1% to <1%, light green for 1% to <3%, yellow for 3% to <5%, orange for 5% to <7%, and red for 7% to 9+%. Undefined regions are gray. (A-D) Side views of PAR4. (E) Top view and (F) bottom view.