| Abstract
| - The Human Genome Project as well as sequencing of the genomes of other organisms offersa wealth of DNA targets for both therapeutic and diagnostic applications, and it is important to developadditional DNA binding motifs to fully exploit the potential of this new information. We have recentlyfound that an aromatic dication, DB293, with an amidine-phenyl-furan-benzimidazole-amidine structurecan recognize specific sequences of DNA by binding in the minor groove as a dimer [Wang, L., Bailly,C., Kumar, A., Ding, D., Bajic, M., Boykin, D. W., and Wilson, W. D. (2000) Proc. Natl. Acad. Sci.U.S.A. 97, 12−16]. The dimer binding is strong, highly cooperative and, in contrast to many closelyrelated heterocyclic dications, has both GC and AT base pairs in the minor groove binding site. Thearomatic heterocycle stacked dimer is quite different in structure from the polyamide-lexitropsin typecompounds, and it is a dication while all lexitropsin dimers are monocations. The heterocyclic dimerrepresents only the second small molecule class that can recognize mixed sequences of DNA. To test thestructural limits on the new type of complex, it is important to probe the influence of compound charge,chemical groups, and structural features. The effects of these compound molecular variations on DNAcomplex formation with several DNA sequences were evaluated by DNase I footprinting, CD and UVspectroscopy, thermal melting, and quantitative analysis with surface plasmon resonance biosensor methods.Conversion of the amidines to guanidinium groups does permit the cooperative dimer to form but removalof one amidine or addition of an alkyl group to the amidine strongly inhibited dimer formation. Changingthe phenyl of DB293 to a benzimidazole or the benzimidazole to a phenyl or benzofuran also inhibiteddimer formation. The results show that formation of the minor groove stacked−dimer complex is verysensitive to compound structure. The discovery of the aromatic dimer mode offers new opportunities toenhance the specificity and expand the range of applications of the compounds that target DNA.
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