Revealing the groove binding characteristics of plant growth regulator 3-indoleacetic acid with calf thymus DNA

Abstract

3-Indoleacetic acid (IAA), a broad-spectrum and efficient plant growth regulator, has been widely used in crop production. However, the accumulation of IAA in human body is potentially harmful to the human health. In this work, the binding properties of calf thymus DNA (ctDNA) with IAA and the impacts of IAA on ctDNA conformation were investigated through modern analysis techniques, including multispectroscopic methods, electrophoresis analysis and molecular docking. The results of fluorescence spectra analysis showed that ctDNA can cause significant fluorescence quenching of IAA in a static manner. The binding process was spontaneous and exothermic, which was mainly driven by van der Waals forces, and the binding constant was 5.58 × 103 L mol−1 at 25 °C. IAA bound to ctDNA via groove mode as revealed through iodine ion quenching assays, viscosity and melting temperature measurements. The molecular docking and Fourier transform infrared spectra intuitively displayed that IAA tended to bind to the G−C base-pairs of the minor grooves of ctDNA, but this binding did not lead to significant damage of DNA which was confirmed by the circular dichroism and gel electrophoresis analyses. These findings may provide novel insights into the toxic mechanism of IAA.