Molecular surface representation for the structure of the NUDT9 and NUDT9-H domains. (A) The side view of molecular surface representation for the NUDT9 structure. The previously proposed critical residues (W110, N168, M216, R273, M280, and D305) are highlighted in red. (B) The side view of molecular surface representation for the structure of NUDT9-H domain. The same critical residues shown in A are labeled in red. (C) Molecular surface representation for the structure of NUDT9 domain binding with R5P in the previously reported model. (D) Molecular surface representation for the structure of NUDT9-H domain binding with ADPR in our structure model. (E) D172, R204, E234, R273, and H324 residues labeled in red interact with R5P in the crystal structure of the NUDT9 protein. (F) Y1349, L1379, E1409, R1433, and H1488 residues that were reported to interact with R5P are labeled in in our NUDT9-H structure to interact with ADPR.