FIGURE 4.

Active site of CPV resolvase. A, stereo view of active site electron density (2mF_o − DF_c; contoured at 1σ) showing the Mg²⁺-water cluster bound at site A and the five acidic active site residues. B and C, active sites of CPV resolvase (B) and RNase H1 (C) bound to a DNA-RNA hybrid (PDB code 2QKK). Metal coordination and Asp-water hydrogen bonds are drawn as dashed lines. The substrate scissile phosphate is expected to displace one of the water molecules coordinated to Mg²⁺ in the CPV resolvase A site. Asp¹³⁰ and Asp¹³⁴ stabilize a Mg²⁺-bound water through hydrogen bonding.