title: Spectroscopic study on the binding of a cationic porphyrin to DNA G-quadruplex under different K+ concentrations.
abstract: We have performed systematic spectroscopic titrations to characterize the binding reaction of cationic meso-tetrakis(4-(N-methylpyridiumyl))porphyrin (TMPyP4) with the G-quadruplex (G4) of human telomeric single-strand oligonucleotide d[TAGGG(TTAGGG)3T] (S24), for which special effort was made to examine the TMPyP4-G4 binding stoichiometry, the binding modes, and the conformational conversion of the G4 structure under different potassium ion (K+) concentration. It is found that, in the presence of 0, 10 mM, and 100 mM K+, TMPyP4 forms a complex with the anti-parallel G4 in a TMPyP4-to-G4 molar ratio of 5, 5 and 3, respectively, and the increase of K+ concentration would reduce the binding affinity of TMPyP4 to G4. For the TMPyP4-G4 complex, the end-stacking mode and groove binding mode were presumed mainly by the results of time-resolved fluorescence spectroscopy in the three cases. Most importantly, it is found that TMPyP4 can directly induce the formation of the anti-parallel G4 structure from the single-strand oligonucleotide S24 in the absence of K+, and that it can preferentially induce the conformational conversion of the G4 structure from the hybrid-type to the anti-parallel one in the presence of K+.
authors.affiliation: School of Life Science and Technology, Beijing Institute of Technology, Beijing, 100081, China.
authors.forename: Hui-Juan
authors.initials: HJ
authors.lastname: Zhang
authors.forename: Xue-Fei
authors.initials: XF
authors.lastname: Wang
authors.forename: Peng
authors.initials: P
authors.lastname: Wang
authors.forename: Xi-Cheng
authors.initials: XC
authors.lastname: Ai
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Zhang
mesh_terms: D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D009690:Nucleic Acid Conformation; D011166:Porphyrins / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D011166:Porphyrins; D004247:DNA; D011188:Potassium