Interaction of berenil with the EcoRI dodecamer d(CGCGAATTCGCG)2 in solution studied by NMR

The conformation of the EcoRI dodecamer d(CGCGAATTCGCG)2 has been examined in solution by 1H and 31P NMR. Spin-spin coupling constants and nuclear Overhauser (NOE) enhancement spectroscopy show that all deoxyriboses lie in the south domain, with a small admixture of the north conformation (0-20%). The time dependence of the nuclear Overhauser enhancements also reveals a relatively uniform conformation at the glycosidic bonds. The average helical twist is 36.5. Tilt angles are small, and roll angles are poorly determined. Both the NOE intensities and 31P relaxation data imply conformational anomalies at the C3-G4/C9-G10 and the A5-A6/T7-T8 steps. Berenil binds in 1:1 stoichiometry to the dodecamer with high affinity and causes substantial changes in chemical shifts of the sugar protons of nucleotides Ado 5-Cyt 9 and of the H2 resonances of the two Ado residues. NOEs are observed between the aromatic protons of berenil and the H1' of both Thy 7 and Thy 8, as well as to Ado 5 and Ado 6 H2. These results firmly establish that berenil binds via the minor groove and closely approaches the nucleotides Ado 6, Thy 7, and Thy 8. Using the observed NOEs between the ligand and the DNA together with the derived glycosidic torsion angles, the authors have built models that satisfy all of the available solution data