DNA-fiber EPR spectroscopy as a tool to study DNA–metal complex interactions: DNA binding of hydrated Cu(II) ions and Cu(II) complexes of amino acids and peptides

DNA-fiber EPR spectroscopy and its application to studies of the DNA binding orientation and dynamic properties of Cu(II) ions and their complexes with amino acids and peptides are reviewed. Cu(II) ions bind in at least two different binding modes; one mode was mobile while the other mode fixed the orientation of the coordination plane. The hydroxyl groups of l-Ser and l-Thr fixed the coordination plane of their respective Cu(II) complexes parallel to the DNA base pair plane, whereas Cu(II) complexes of Lys and Arg induced several binding modes, depending on the tertiary structure of the DNA and the chirality of the amino acids. Unusually broadened signals observed for the His complex were assigned to a mono-l-His complex stacked stereospecifically along the DNA double helix. In comparison, Cu(II)·Xaa-Xaa′-HisCu(II)·Xaa-Xaa′-His type complexes oriented in the minor groove with different affinities and extents of randomness depending on the Xaa-Xaa′Xaa-Xaa′ sequence and the chirality of Xaa or Xaa′Xaa′ while the C-terminal Xaa residues in Cu(II)·Arg-Gly-His-Xaa (Xaa = l-Leu or l-Glu) decreased the stereospecificity and the stability of the complexes bound to DNA. In contrast to Xaa-Xaa′-HisXaa-Xaa′-His complexes, the coordination planes of Cu(II)·Gly-l-His-Gly and Cu(II)·Gly-l-His-l-Lys complexes were found to lie parallel to the DNA-fiber axis. Dinuclear Cu(II)·carnosine complexes were also shown to bind to DNA stereospecifically.