a The domain structure, crystal packing and overall structure of the mAPE1 blunt-ended dsDNA product complex. The redox domain and nuclease domain are colored in orange and green, respectively. b The schematic presentation of the two dsDNAs in the two product complex structures. Bottom right panel: structural alignment of the two dsDNAs in the two product complex structures. The active sites are highlighted by blue circles. c Structural alignment of mAPE1 blunt-ended dsDNA product complex and hAPE1-substrate DNA complex (PDB entry: 5WN5). It can be seen that the last nucleotide in the 3′-end of dsDNA in our product complex is missing. Only the scissile strand of dsDNA in the hAPE1-substrate DNA complex (colored in orange) is displayed. d Superposition of active sites in mAPE1 blunt-ended dsDNA product complex and hAPE1-substrate DNA complex. The active site residues in the hAPE1-substrate DNA complex are colored by light orange and displayed in a transparent mode.