Structural basis for the sequence-specific DNA strand cleavage by the enediyne neocarzinostatin chromophore. Structure of the post-activated chromophore-DNA complex.

Neocarzinostatin chromophore (NCS chrom) belongs to a family of highly potent enediyne antitumor antibiotics which bind to specific DNA sequences and cause single- and/or double-strand lesions. NCS chrom-DNA complexes have eluded structural studies since the native form of the drug is extremely labile in aqueous conditions. We report the three-dimensional structure of the stable glutathione post-activated NCS chrom (NCSi-glu)-DNA complex [NCSi-glu-d(GGAGCGC).d(GCGCTCC)] using NMR and distance geometry-molecular dynamics simulation methods. NCSi-glu interacts with the GCTC tetranucleotide on one strand and with the AGC trinucleotide on the other strand through the unique intercalation at the 5'-CT/5'-AG step and minor groove binding. The DNA-drug complex exhibits an extended, unwound V-shaped intercalation site and wider and shallower grooves than the free DNA duplex. The structure of the complex manifests specific van der Waals interactions and H-bond formation between the carbohydrate moiety and a specific DNA sugar/phosphate. Prominent among those are the contacts of the NCSi-glu residues with the functional groups in the minor groove that are characteristic of individual DNA bases. These results provide a structural model for understanding the sequence specificity of the single- and double-strand cleavage at the AGC and related sites by the enediyne NCS chrom.