INTERACTION OF MANGANESE(II), COBALT(II) AND NICKEL(II) WITH DNA OLIGOMERS STUDIED BY H-1-NMR SPECTROSCOPY

The metal binding properties of three different oligodeoxyribonucleoti des, one decamer and two dodecamers, have been studied by 1D and 2D H- 1 NMR spectroscopy. The sequential composition of the oligomers was ch osen so as to provide a multitude of different binding site contexts: 5'-GACGGCCGTC (I), 5'-CGCGAATTCGCG (II), and 5'-ATGGGTACCCAT (III). Sa lts of three different metal ions: Mn(II), Co(II) and Ni(II), were use d in titration experiments. The binding studies were carried out under duplex conditions. The influence of paramagnetic metal ions on proton s adjacent to the binding site were followed by measuring line broaden ing and T-1 relaxation times. We have previously proposed a rule for s equence-selective metal binding to G-N7 in oligodeoxyribonucleotides w here the metal prefer the 5'-guanine residue in the order: 5'-GG great er than or equal to GA > GT much greater than GC. This binding pattern is also observed in the present study for Mn(II) and Co(II). However, in sequence I Ni(II) does not follow the established selectivity rule showing greater affinity for 5'-G in the context 5'-GC than in the co ntext 5'-GA. For II and III Ni(II) ions are seen tb follow the selecti vity rule. Fluctuation in the nucleophilicity of G-N7 along the duplex is probably a consequence of sequence-dependent variation in pi-stack ing interaction between base residues. (C) 1998 Elsevier Science S.A. All rights reserved.