title: Parallel G-quadruplex-specific fluorescent probe for monitoring DNA structural changes and label-free detection of potassium ion.
abstract: Here we demonstrate an anionic porphyrin, protoporphyrin IX (PPIX), as a parallel G-quadruplex-specific fluorescent probe for monitoring DNA structural changes and utilize it to develop a DNA-based K(+) sensor. The interactions of PPIX with different DNA structures in K(+) or Na(+) solution are investigated by using circular dichroism, fluorescence, and UV-vis spectroscopy. The observations reveal that PPIX has an ∼100-fold selectivity for parallel G-quadruplexes against duplexes and antiparallel G-quadruplexes. Meanwhile, the fluorescence intensity of PPIX increases by over 10-fold upon binding to parallel G-quadruplexes. On the basis of the selectivity and fluorescence property of PPIX, we introduce a facile, label-free approach to monitoring DNA structural changes via fluorescence signal readout that is tuned by PPIX binding and release. To illustrate it, we utilize PPIX and a G-rich DNA PS2.M to construct a fluorescent K(+) sensor based on an antiparallel-to-parallel conformation transition of the G-quadruplex. PS2.M adopts an antiparallel quadruplex structure in Na(+) solution, whereas it gradually converts into a parallel G-quadruplex upon addition of increasing K(+). This conformational change is indicated by a sharp increase in the fluorescence intensity of PPIX, owing to the good ability of PPIX to discriminate parallel G-quadruplexes from antiparallel ones. Even in the presence of 100 mM Na(+), such a "turn-on" fluorescent sensor can respond to low concentrations of K(+), with a limit of detection (0.5 mM) for K(+) analysis. In addition, this sensor exhibits a high selectivity for K(+) over other common metal ions, which ensures its practical applications to real samples. These results reveal that PPIX is promising for use as a specific DNA structural probe in sensing applications.
authors: State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, China.
authors: Tao
authors: T
authors: Li
authors: Erkang
authors: E
authors: Wang
authors: Shaojun
authors: S
authors: Dong
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D004247:DNA / Q000737:chemistry* / Q000187:drug effects; D005456:Fluorescent Dyes / Q000032:analysis / Q000378:metabolism*; D054856:G-Quadruplexes / Q000187:drug effects; D011188:Potassium / Q000032:analysis* / Q000737:chemistry / Q000494:pharmacology; D011524:Protoporphyrins / Q000032:analysis / Q000378:metabolism*; D012964:Sodium / Q000032:analysis / Q000737:chemistry / Q000494:pharmacology; D013057:Spectrum Analysis; D013379:Substrate Specificity
chemical_list: D005456:Fluorescent Dyes; D011524:Protoporphyrins; D004247:DNA; D012964:Sodium; C028025:protoporphyrin IX; D011188:Potassium