Selective binding to AT sequences in DNA by an acridine-linked peptide containing the SPKK motif

The sequence selectivity of binding to DNA by an acridine-linked peptide ligand has been investigated by means of footprinting methodologies. The ligand conjugates an anilino-acridine intercalating chromophore with the potentially minor groove binder octapeptide SPKKSPKK. This basic peptide corresponds to a highly conserved DNA recognition motif found in histone H1 and several other nonhistone proteins. Three complementary techniques using DNase I, hydroxyl radicals and osmium tetroxide as sequencing probes have been employed to evaluate both the sequence specificity of binding and the drug-induced conformational changes in DNA. The results converge to demonstrate the AT-selectivity and support a model in which the peptide moiety lies in the minor groove. DNA-binding sites of the conjugate are restricted to a few alternating AT-sequences proximal to GC-rich regions. Binding to homooligomeric runs of A and T is clearly disfavoured by the hybrid whereas such sequences represent preferred binding sites for the unsubstituted basic peptide. These differences reflect the influence of the anilino-acridine chromophore, which evidently contributes to the DNA recognition process allowing the peptide only to contact defined DNA sequences.