5,10,15,20-Tetra-(N-methyl-3-pyridyl)porphyrin destabilizes the antiparallel telomeric quadruplex d(TTAGGG)4 |
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Authors: | Yu. V. Dutikova O. F. Borisova A. K. Shchyolkina J. Lin S. Huang A. A. Shtil D. N. Kaluzhny |
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Affiliation: | 1.Blokhin Cancer Research Center,Russian Academy of Medical Sciences,Moscow,Russia;2.Engelhardt Institute of Molecular Biology,Russian Academy of Sciences,Moscow,Russia;3.National Yang-Ming University,Taipei,Taiwan (Republic of China);4.National Defense Medical Center,Taipei,Taiwan (Republic of China) |
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Abstract: | 5,10,15,20-Tetra-(N-methyl-3-pyridyl)porphyrin (TMPyP3) is a DNA-binding derivative of porphyrins. A comparative study of the binding of this ligand to biologically significant DNA structures was performed. For this purpose, the interactions of TMPyP3 with the antiparallel telomeric G-quadruplex d(TTAGGG)4, oligonucleotide dTTAGGGTTAGAG(TTAGGG)2 (not forming a quadruplex structure), double-stranded d(AC)8 · d(GT)8, and single-stranded d(AC)8 and d(GT)8 DNA molecules have been studied. Analysis of absorption isotherms has demonstrated that the binding constants and the number of binding sites for the complexes TMPyP3: DNA increase in the following order: d(AC)8 < d(GT)8 < d(AC)8 · d(GT)8 = d(TTAGGG)4 < dTTAGGGTTAGAG(TTAGGG)2. It has been for the first time demonstrated that the constant for TMPyP3 binding to unfolded dTTAGGGTTAGAG(TTAGGG)2 strand (1.3 × 107 M−1) is approximately threefold higher than for the G-quadruplex d(TTAGGG)4 (4.7 × 106 M−1). Binding of two TMPyP3 molecules to d(TTAGGG)4 decreases the thermostability of G-quadruplex (ΔTm = −8°C). Circular dichroism spectra of the TMPyP3 complexes with d(TTAGGG)4 suggest that the ligand partially unfolds the G-quadruplex structure. Structural destabilization of the telomeric G-quadruplex by TMPyP3 can explain the relatively low activity of this ligand as a telomerase inhibitor and a low cytotoxicity for cultured tumor cells. |
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