Book of Abstracts: Albany 2007
June 19-23 2007
DNA Binding Properties of Dye Hoechst 33258 Derivatives Containing Bulky Substituents in the Phenyl Ring
We employed UV-VIS spectroscopy, fluorescence methods and circular dichroism spectroscopy (CD) to study the interaction of dye Hoechst 33258, Hoechst 33342 and their derivatives with poly[d(AT)]⋅poly[d(AT)], poly(dA) )]⋅poly(dT) and DNA oligomers with the sequences 5'-CGTATATATACG-3' and 5'-CCTATATCC-3'.
We identified three types of complexes formed by Hoechst 33258 and Hoechst 33342 with DNA. These compounds bind to poly(dA) )]⋅poly(dT) and duplex 5'-CCTATATCC-3' mainly in the monomer form and bind to the DNA dodecamer with the sequence 5'-CGTATATATACG-3' both in the monomer and dimer forms. In a dimer complex, the two dye molecules are sandwiched in the same place of the minor DNA groove . The complex geometry exhibits similarity with the crystal structure of an oligonucleotide complex containing two distamycin molecules bound side-by-side in the minor groove . Our data show that Hoechst 33258 and Hoechst 33342 form also nonspecific complexes which correspond to the interaction of the dye associates with DNA phosphate groups. The attachment of the methyl group to the phenyl ring of Hoechst 33258 and the replacement of OH group by dimethylamino group (Methylproamine) reduces nonspecific binding of the dye with a concomitant increase in the contribution of AT-specific monomer and dimer complexes. A Hoechst 33258 derivative containing isopropyl group in the phenyl ring ( Isopropylproamine) binds to DNA only in the monomer form and exhibits very weak affinity for DNA. This may reflect the fact that bulky isopropyl group prevents nonspecific binding of the dye associates to DNA and creates a sterical hindrance for accomodation of the dimer dye species into the minor DNA groove. Our results show that specificity and affinity of Hoechst 33258 derivatives for DNA and their modes of binding can be controlled by introduction of bulky chemical groups in the phenyl ring of the dye molecule. The possible implications of these results in design of new sequence-specific DNA-binding ligands and understanding the mechanism underlying Hoechst-mediated radioprotection will be discussed.
References and Footnotes
V.A. Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow 119991, Russia