The interactions of three related cationic porphyrins, TMPyP4, TMPyP3 and TMPyP2, with a WT 39-mer Bcl-2 promoter sequence G-quadruplex were studied using Circular Dichroism, ESI mass spectrometry, Isothermal Titration Calorimetry, and Fluorescence spectroscopy. The planar cationic porphyrin TMPyP4 (5, 10, 15, 20-meso-tetra (N-methyl-4-pyridyl) porphine) is shown to bind to a WT Bcl-2 G-quadruplex via two different binding modes, an end binding mode and a weaker mode attributed to intercalation. The related non-planar ligands, TMPyP3 and TMPyP2, are shown to bind to the Bcl-2 G-quadruplex by a single mode. ESI mass spectrometry experiments confirmed that the saturation stoichiometry is 4:1 for the TMPyP4 complex and 2:1 for the TMPyP2 and TMPyP3 complexes. ITC experiments determined that the equilibrium constant for formation of the (TMPyP4)1/DNA complex (K1 = 3.7 ? 10(6)) is approximately two orders of magnitude greater than the equilibrium constant for the formation of the (TMPyP2)1/DNA complex, (K1 = 7.0 ? 10(4)). Porphyrin fluorescence is consistent with intercalation in the case of the (TMPyP4)3/DNA and (TMPyP4)4/DNA complexes. The non-planar shape of the TMPyP2 and TMPyP3 molecules results in both a reduced affinity for the end binding interaction and the elimination of the intercalation binding mode.
Public Library of Science
College of Arts and Sciences
Department of Chemistry
Base Sequence, Calorimetry, Cations, Circular Dichroism, Electrospray Ionization, Fluorescence, Genetic, G-Quadruplexes, Ligands, Mass, Porphyrins, Porphyrins: chemistry, Porphyrins: metabolism, Promoter Regions, Proto-Oncogene Proteins c-bcl-2, Proto-Oncogene Proteins c-bcl-2: genetics, Solutions, Spectrometry, Thermodynamics
Le VH, Nagesh N, Lewis EA (2013) Bcl-2 Promoter Sequence G-Quadruplex Interactions with Three Planar and Non-Planar Cationic Porphyrins: TMPyP4, TMPyP3, and TMPyP2. PLoS ONE 8(8): e72462. https://doi.org/10.1371/journal.pone.0072462