Characterization of interactions between the pyrophosphate of ADPR and the NUDT9-H domain. (A) Ribbon presentation of the pyrophosphate binding pockets in the NUDT9-H domain (gray). The interactions are denoted with yellow dashed lines. (B–E) Characterization of the ADPR concentration–current response relationship for the WT (dashed line) and the indicated mutant (continuous line) of the TRPM2 channels. The insets in B–E represent summary of the currents from additional mutants of the indicated residues when activated by 100 µM (black) or 3 µM (gray) ADPR. Data in B–E are expressed as mean ± SEM from at least five independent repetitions.