End-stacking of copper cationic porphyrins on parallel-stranded guanine quadruplexes

Sarah E. Evans, Miguel A. Mendez, Kevin B. Turner, Loryn R. Keating, Ryan T. Grimes, Sarah Melchoir, Veronika A. Szalai

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91 Scopus citations


Nucleic acids that contain multiple sequential guanines assemble into guanine quadruplexes (G-quadruplexes). Drugs that induce or stabilize G-quadruplexes are of interest because of their potential use as therapeutics. Previously, we reported on the interaction of the Cu2+ derivative of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine (CuTMpyP4), with the parallel-stranded G-quadruplexes formed by d(T4GnT 4) (n = 4 or 8) (Keating and Szalai in Biochemistry 43:15891-15900, 2004). Here we present further characterization of this system using a series of guanine-rich oligonucleotides: d(T4GnT4) (n = 5-10). Absorption titrations of CuTMpyP4 with all d(T4G nG4) quadruplexes produce approximately the same bathochromicity (8.3 ± 2 nm) and hypochromicity (46.2-48.6%) of the porphyrin Soret band. Induced emission spectra of CuTMpyP4 with d(T 4GnT4)4 quadruplexes indicate that the porphyrin is protected from solvent. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry revealed a maximum porphyrin to quadruplex stoichiometry of 2:1 for the shortest (n = 4) and longest (n = 10) quadruplexes. Electron paramagnetic resonance spectroscopy shows that bound CuTMpyP4 occupies magnetically noninteracting sites on the quadruplexes. Consistent with our previous model for d(T4G4T 4), we propose that two CuTMpyP4 molecules are externally stacked at each end of the run of guanines in all d(T4GnT 4) (n = 4-10) quadruplexes.

Original languageEnglish
Pages (from-to)1235-1249
Number of pages15
JournalJournal of Biological Inorganic Chemistry
Issue number8
StatePublished - Nov 2007
Externally publishedYes


  • Copper porphyrin
  • End-stacking
  • Fourier transform ion cyclotron resonance mass spectrometry and electron paramagnetic resonance spectroscopy
  • Guanine quadruplex
  • Guanine quartet


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