title: Mass spectrometric studies on effects of counter ions of TMPyP4 on binding to human telomeric DNA and RNA G-quadruplexes.
abstract: A comparative study on human telomeric DNA G-quadruplex binding of meso-5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4) between its two salt forms, i.e., tetratosylate and tetrachloride, was conducted by using ESI-TOF-MS, UV-melting measurement, and molecular modeling methods. Besides cation TMPyP4, the tosyl anion was found to bind to human telomeric DNA G-quadruplex with multiple binding stoichiometries from 1:1 to 3:1 observed in ESI-TOF-MS spectra, indicating that the stabilization activity of TMPyP4 tetratosylate on G-quadruplex is derived from a synergetic effect of both TMPyP4 cation and tosyl anion. A molecular modeling study suggests that a tosyl anion fills up the vacant space between TMPyP4 cation and DNA G-quadruplex and thus stabilizes the complex by 3.8 kcal/mol. Therefore, it is estimated that TMPyP4 tetratosylate's activity might not reflect the real effect of TMPyP4 cation in some bioassays related to G-quadruplex stabilization. This was verified by the results of less binding affinity of TMPyP4 tetrachloride with DNA G-quadruplex obtained from ESI-TOF-MS measurement, and of 2.27 °C less thermal stabilization of TMPyP4 tetrachloride for DNA G-quadruplex, compared to its tetratosylate under the same conditions. Our study demonstrated the influence of counter ions of TMPyP4 on G-quadruplex binding, which sheds light on the proper usage of TMPyP4 salt in the chemical and biological research associated with G-quadruplex binding. Subsequently, the binding of TMPyP4 tetrachloride to human telomeric RNA G-quadruplexes was studied with ESI-TOF-MS technique. The binding constants of TMPyP4 with human telomeric G-quadruplexes indicated that TMPyP4 binds to human telomeric RNA G-quadruplex one order of magnitude stronger than DNA counterpart. This is a comprehensive mass spectrometric report on binding study of TMPyP4 with human telomeric DNA/RNA G-quadruplexes.
authors.affiliation: State Key Laboratory of Quality Research in Chinese Medicine, and Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau.
authors.forename: Li-Ping
authors.initials: LP
authors.lastname: Bai
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Li
authors.initials: L
authors.lastname: Han
authors.forename: Hing-Man
authors.initials: HM
authors.lastname: Ho
authors.forename: Renxiao
authors.initials: R
authors.lastname: Wang
authors.forename: Zhi-Hong
authors.initials: ZH
authors.lastname: Jiang
mesh_terms: D001681:Biological Assay; D004247:DNA / Q000737:chemistry*; D054856:G-Quadruplexes; D006801:Humans; D007477:Ions / Q000737:chemistry*; D013058:Mass Spectrometry; D008958:Models, Molecular; D011166:Porphyrins / Q000737:chemistry*; D011485:Protein Binding; D012313:RNA / Q000737:chemistry*; D012492:Salts / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet; D016615:Telomere / Q000648:ultrastructure
chemical_list: D007477:Ions; D011166:Porphyrins; D012492:Salts; C021096:tetra(4-N-methylpyridyl)porphine; D012313:RNA; D004247:DNA