INTERACTION OF DNA-THREADING PEPTIDE-AMSACRINE CONJUGATES WITH DNA AND CHROMATIN

The SPKK peptide motif which functions as a DNA minor groove binding u nit in various chromosomal and gene regulatory proteins has been attac hed to the antitumour drug amsacrine in order to reinforce interaction with DNA. Two bifunctional molecules in which an amsacrine-4-carboxam ide derivative is linked to one or two SPKK motifs via a diaminopropyl tether have been designed and synthesized. We have applied various sp ectroscopic methods (absorption, circular and linear dichroism) to del ineate the role of the peptide moiety as opposed to the chromophoric a cridine moiety in the interaction of the conjugates with both DNA and chromatin. The structural and kinetic data concur that the two peptide conjugates thread through the DNA double helix so as methanesulphonan ilino group positioned within the minor and major grooves of the doubl e helix respectively. The threading-type intercalation process, eviden ced by stopped-flow measurements, is not affected when the DNA is wrap ped around histones. Linkage of the SPKK peptide motif to intercalatin g drugs represents an efficient system to stabilize drug-DNA complexes .