title: Interaction between cationic zinc porphyrin and lead ion induced telomeric guanine quadruplexes: evidence for end-stacking.
abstract: The interaction between small molecules and telomeric quadruplex DNA has received great attention because of its importance in molecular recognition and anticancer drug design. Using UV/vis absorption titration, thermal melting, circular dichroism spectroscopy, and electrospray ionization mass spectrometry, we examined the formation of lead ion induced guanine quadruplexes (Pb-G4) from oligonucleotide AG(3)(T(2)AG(3))(3) and their interaction with a zinc derivative of 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (Zn-TMPyP). The binding of lead ion to the oligonucleotide was found to have an unusually high affinity and followed a 1:1 stoichiometry, and the resultant Pb-G4 structure was stabilized by Zn-TMPyP binding. Owing to the steric hindrance of the axial ligand of zinc and also the relatively rigid structure of Pb-G4, intercalation of Zn-TMPyP between adjacent guanine quartets is precluded, thus allowing the end-stacking binding mode to be characterized exclusively. In conjunction with a big redshift (more than 8 nm) in the absorption spectrum, we demonstrate that a conservative induced circular dichroism is an important signature for end-stacking of porphyrins on guanine quadruplexes.
authors.affiliation: State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116012, People's Republic of China.
authors.forename: Jingxi
authors.initials: J
authors.lastname: Pan
authors.forename: Suping
authors.initials: S
authors.lastname: Zhang
mesh_terms: D002942:Circular Dichroism; D054856:G-Quadruplexes; D006801:Humans; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry; D007854:Lead / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D016615:Telomere / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D007477:Ions; D009942:Organometallic Compounds; D011166:Porphyrins; D007854:Lead; C021096:tetra(4-N-methylpyridyl)porphine; D015032:Zinc