Structure determination

The crystal structure of hEXOG:Mg²⁺ was determined by molecular replacement using Phaser and Drosophila EndoG (PDB accession number 3ISM) as search model³⁹. The missing Wing domain was built using Coot⁴⁰, and refined using Phenix⁴¹. Crystal structures of hEXOG–DNA complexes were determined by molecular replacement using the apo EXOG structure. MolProbity⁴² was used to evaluate the final structures. Single-wavelength anomalous dispersion data were collected for apo and DNA complex containing Mn²⁺. The crystal structures of hEXOG:Mn²⁺ and hEXOG:DNA:Mn²⁺ were determined by molecular replacement using hEXOG:Mg²⁺ and hEXOG–DNA structure as respective models. Metal locations were determined from an anomalous difference map. After refinement, Ramachandran favoured residues were ≥;98% and Ramachandran outlier residues were ≤0.57% for all four structures. All structural figures were prepared using PyMol.