How amino acids control the binding of Cu(II) ions to DNA .2. Effect of basic amino acid residues and the chirality on the orientation of the complexes

The binding structures of bis-lysine and bis-arginine complexes 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 theta approximate to 45 degrees 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. (C) 1997 Elsevier Science Inc.