Bcl-2 promoter sequence G-quadruplex interactions with three planar and non-planar cationic porphyrins: TMPyP4, TMPyP3, and TMPyP2

• Published in: PloS one 2013-08, Vol.8 (8), p.e72462-e72462
• Main Authors: Le, Vu H, Nagesh, Narayana, Lewis, Edwin A
• Format: Article
• Language: English
• Subjects: Base Sequence; Bcl-2 protein; Binding; Biochemistry; Calorimetry; Cations; Chemistry; Circular Dichroism; Deoxyribonucleic acid; Dichroism; DNA; Equilibrium; Extinction; Fluorescence; Fluorescence spectroscopy; G-Quadruplexes; Intercalation; Ligands; Mass spectrometry; Mass spectroscopy; Porphyrins; Porphyrins - chemistry; Porphyrins - metabolism; Promoter Regions, Genetic; Proto-Oncogene Proteins c-bcl-2 - genetics; Solutions; Spectrometry, Fluorescence; Spectrometry, Mass, Electrospray Ionization; Spectroscopy; Stoichiometry; Telomerase; Thermodynamics; Titration; Titration calorimetry
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0072462

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.