Fig. 1

DAC-TP, but not AZA-TP, is an allosteric activator and substrate of SAMHD1. a Chemical structures of dCTP, decitabine triphosphate (DAC-TP), and azacytidine triphosphate (AZA-TP). b–d dNTPase activity assay for recombinant SAMHD1. The rate of hydrolysis for the indicated nucleotide triphosphates was quantified in the presence of (b) buffer alone, (c) GTP, which can occupy allosteric site 1 (A1), or (d) dGTP, which can occupy A1 and allosteric site 2 (A2). Cat: Catalytic site. e Size-exclusion chromatograms of SAMHD1 in absence of nucleotide (yellow line) or in the presence of GTP alone (gray dashed line), DAC-TP alone (orange dashed line), GTP + DAC-TP (orange line), GTP + AZA-TP (blue line), or GTP + dCTP (black line). f Sedimentation velocity of SAMHD1 incubated in the presence of GTP in combination with either AZA-TP or DAC-TP. g Structure of the SAMHD1 tetramer in complex with DAC-TP. Each SAMHD1 subunit is shown as a surface representation, colored in light pink, deep teal, light green and wheat. In the insets, nucleotides are shown as sticks. (Top, right panel) An overlay of SAMHD1 structures in complex with dCTP (PDB ID: 4TNP; gray) or DAC-TP (light pink) in allosteric site 2. (Bottom, right panel) An overlay of SAMHD1 structures in complex with dCTP (PDB ID: 4TNP; gray) or DAC-TP (deep teal) in the catalytic pocket