Controlling interactions between peptide-heme and G-quadruplex DNA using Fe-bound NH3 and H2O ligands

Abstract

Developing ligands that improve the stability of G-quadruplex DNA (G4) is a promising anticancer strategy. We constructed a peptide-heme-NH₃/G4 hybrid complex possessing a unique NH₃ axial ligand between the heme and G-quartet planes. The interface between the heme and G-quartet planes is well adapted to accommodate an NH₃ molecule, with a ligand substituent constant (K_s) from 98 733 ± 7141 to 18 357 ± 284 M⁻¹ at 15–35 °C. Compared with free peptide-heme-H₂O, complexation with G4 resulted in a 22–35-fold increase in K_s value. The binding constant (K_a) between peptide-heme-NH₃ and G4 was determined to be between 37.6 ± 4.9 and 121.8 ± 3.0 μM⁻¹ at 15–35 °C, 21–30-fold higher than the value observed for the peptide-heme-H₂O/G4 hybrid complex. Thermodynamic analysis of experimental data showed that interactions between the heme and G-quartet planes are highly sensitive to Fe-bound NH₃ and H₂O ligands, which significantly enhance the thermal stability of G4 through an enthalpy-driven ligand substituent reaction and an entropy-driven complexation reaction. These findings provide novel insights and mechanistic clues for designing anticancer metal complexes targeting G4.