Spectroscopic studies on the binding properties of Zn-PP with various human telomeric G-quadruplex DNA and ct-DNA

Abstract

The binding property of Zn-PP with human telomeric G-quadruplex DNA as compared to binding with ct-DNA is examined by UV-vis, fluorescence and CD spectroscopic methods. UV-vis absorption spectral analysis in the presence of K⁺, shows that addition of three types of human telomeric G-quadruplex DNA (Htel-G₄, Htel-1-G₄ and Htel-2-G₄) in the Zn-PP solution induces moderate hypochromicity with intrinsic binding constants of (3.13±0.45)×10⁵, (1.47±0.12)×10⁵ and (2.51±0.16)×10⁵<i style="mso-bidi-font-style:normal">M</i>^-1, respectively, while for ct-DNA, the <i style="mso-bidi-font-style:normal">K</i>_b value is (9.94±0.32)×10⁴ <i style="mso-bidi-font-style:normal">M</i>^-1. In the fluorescence emission spectral analysis, the addition of G-quadruplex DNA induces significant quenching of the fluorescence emission of Zn-PP with total quenching ratios of 26.31–36.84%, while the addition of ct-DNA under the same conditions induces only 17.33% of the quenching ratio of Zn-PP. Both the UV-vis and fluorescence spectral analysis indicate that Zn-PP exhibits higher binding affinity to human telomeric G-quadruplex DNA than to ct-DNA. In the CD spectral analysis, the interaction with Zn-PP does not disturb the characteristic absorption of G-quadruplex at 290 nm corresponding to its antiparallel conformation, and only slightly decreases the positive absorption at 270 nm as a shoulder peak. In comparision, the addition of Zn-PP induces significant spectral changes on the CD absorption of double helix ct-DNA, with a 22.2% increase on the positive peak absorption, along with a 9.63% decrease on the negative peak absorption, which suggests that the antiparallel structure of G-quadruplex is stable in the presence of Zn-PP.