DNA-fiber EPR investigation of the influence of amino-terminal residue stereochemistry on the DNA binding orientation of Cu(II)·Gly-Gly-His-derived metallopeptides

DNA fiber EPR was used to investigate the DNA binding stabilities and orientations of Cu(II)·Gly-Gly-His-derived metallopeptides containing d- vs. l-amino acid substitutions in the first peptide position. This examination included studies of Cu(II)·d-Arg-Gly-His and Cu(II)·d-Lys-Gly-His for comparison to metallopeptides containing l-Arg/Lys substitutions, and also the diastereoisomeric pairs Cu(II)·d/l-Pro-Gly-His and Cu(II)·d/l-Pro-Lys-His. Results indicated that l-Arg/Lys to d-Arg/Lys substitutions considerably randomized the orientation of the metallopeptides on DNA, whereas the replacement of l-Pro by d-Pro in Cu(II)·l-Pro-Gly-His caused a decrease in randomness. The difference in the extent of randomness observed between the d- vs. l-Pro-Gly-His complexes was diminished through the substitution of Gly for Lys in the middle peptide position, supporting the notion that the ε-amino group of Lys triggered further randomization, likely through hydrogen bonding or electrostatic interactions that disrupt binding of the metallopeptide equatorial plane and the DNA. The relationship between the stereochemistry of amino acid residues and the binding and reaction of M(II)·Xaa-Xaa′-His metallopeptides with DNA are also discussed.