How amino acids control the binding of Cu(II) ions to DNA (II): Effect of basic amino acid residues and the chirality on the orientation of the complexes

The binding structures of bis-lysine and bis-arginine comlexes of copper(II) on highly oriented DNA fibers have been investigated by ESR spectroscopy. These complexes bind to DNA in two different modes; species A in one mode has a planar coordination structure as in solution, and species B in the other mode has a distorted planar structure on the DNA. The relative amount of A and B changes with the conformation of the DNA, as well as with the type and chirality of the amino acids. Argine forms A more than lysine. On A-form DNA fibers, A for l-lysine and l-arginine complexes are bound with the angle θ≈45° between the g ∥ axis and the DNA helical axis, while A and B for the d-isomers are almost randomly oriented. l-arginine fixes the orientation of A on A-form DNA fibers more firmly than l-lysine. On B-form DNA fibers, the orientation of the complexes is modulated dynamically, and the g ∥ axes have a tendency to be reoriented along the fiber axis by the conformational change of the DNA from A- to B-form at room temperature. The d-arginine complex on B-form DNA is peculiar in that it rotates more freely than the other complexes at room temperature and shows only the A at low temperature.