State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, China.
Anal Chem. 2010 Sep 15;82(18):7576-80. doi: 10.1021/ac1019446.
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.
在这里，我们展示了一种阴离子卟啉，原卟啉 IX（PPIX），作为一种平行 G-四链体特异性荧光探针，用于监测 DNA 结构变化，并利用它开发一种基于 DNA 的 K(+)传感器。通过使用圆二色性、荧光和紫外-可见光谱研究了 PPIX 在 K(+)或 Na(+)溶液中与不同 DNA 结构的相互作用。观察结果表明，PPIX 对平行 G-四链体具有约 100 倍的选择性，而对双链体和反平行 G-四链体没有选择性。同时，PPIX 与平行 G-四链体结合后，荧光强度增加了 10 倍以上。基于 PPIX 的选择性和荧光性质，我们引入了一种简单、无标记的方法，通过荧光信号读出来监测 DNA 结构变化，该方法通过 PPIX 的结合和释放进行调谐。为了说明这一点，我们利用 PPIX 和富含 G 的 PS2.M DNA 构建了一种基于 G-四链体从反平行到平行构象转变的荧光 K(+)传感器。PS2.M 在 Na(+)溶液中采用反平行四链体结构，而当加入越来越多的 K(+)时，它逐渐转化为平行 G-四链体。这种构象变化表现为 PPIX 的荧光强度急剧增加，这是由于 PPIX 能够很好地区分平行 G-四链体和反平行 G-四链体。即使在存在 100 mM Na(+)的情况下，这种“开启”荧光传感器也可以响应低浓度的 K(+)，对 K(+)分析的检测限（0.5 mM）。此外，该传感器对 K(+)具有很高的选择性，超过其他常见的金属离子，这确保了其在实际样品中的实际应用。这些结果表明，PPIX 有望作为一种用于传感应用的特异性 DNA 结构探针。
