(A) Scheme describing the strategy to characterize CPO-mediated inactivation of KIAA1363 (and CES1) by activity-based protein profiling (ABPP). The activity probe, FP-biotin, is shown in simplified form with a reactive warhead (black circle) attached to a biotin (B) tag (green star). Recombinant CES1 (B) and KIAA1363 (C) proteins were incubated with the indicated concentrations of CPO for 15 min (37°C), followed by addition of FP-biotin (2 μM, 1 h, room temperature). After separation of proteins by SDS-PAGE and avidin-HRP blotting, the intensity of the biotin-labeled CES1 and KIAA1363 proteins were quantified and plotted versus CPO concentration. IC50 values were interpolated from the curves and are indicated on the graphs. Data are representative of two independent experiments.