Astaxanthin Binding Affinity to DNA: Studied By Fluorescence, Surface Plasmon Resonance and Molecular Docking Methods

Carotenoid astaxanthin (Ax), a pink-red pigment, with its anti-oxidative feature, is useful as a therapeutic element for numerous diseases. The purpose of this study is to investigate the binding affinity of Ax to double strand (ds) DNA evaluated by using the fluorescence spectroscopy, surface plasmon resonance (SPR) and docking approaches. The fluorescence results show that Ax can quench the intensity of DNA fluorescence via a static quenching way. In the SPR method, for affinity evaluation, DNA molecules were attached on a gold sensor surface. Using different amounts of ds DNA, the kinetic values KD, KA, and Ka were calculated. The Van't Hoff equation was used to estimate thermodynamic parameters including enthalpy (∆H), entropy (∆S) and Gibbs free energy (∆G) changes. The obtained results for KD in SPR (6.89×10^-5 M) and fluorescence (KD=0.76×10^-5 M) methods were in line with each other. Thermodynamic studies were carried out at four different temperatures, and the resulted negative data for ΔH and ΔS displayed that the main binding strength in the interaction of Ax with DNA was hydrogen bonding. ΔG value calculated by fluorescence method was near -38 kJ. mol^-1 and using the docking method, estimated -9.95 kcal. mol^-1 (-41.63 kJ. mol^-1) which shows the binding behavior has an exothermic and spontaneous mechanism. Molecular docking results confirmed that the side chains of Ax interact specifically with base pairs and the DNA backbone.