Exploring the Binding Mechanism of Flavonoid Quercetin to Phospholipase A2: Fluorescence Spectroscopy and Computational Approach

The interaction of flavonoid Quercetin with Phospholipase A2 isolated from snake venom Bothrops brazili (MTX-II) was investigated by fluorescence spectroscopy and molecular modeling. The fluorimetric titrations were conducted at 288, 298 and 308 K and at pH 8.0. Stern-Volmer quenching constant (KSV) and binding constant (Kb) were calculated along with the corresponding thermodynamic parameters ΔG, ΔH and ΔS at 288 and 298 K. From these analysis evidences of complex formation in between MTX-II and QCT are found. Besides that modified Stern-Volmer plot show evidences for two types of intrinsic fluorophores with different accessibilities at 308 K. The mean distance between the donor (MTX-II) and acceptor (QCT) was determined by fluorescence resonance energy transfer (FRET). The optimized structure of QCT was obtained by ab initio calculation, which geometry was performed in its ground states by using DFT/B3LYP functional with 6-311+G (d,p) basis set. The molecular docking analysis show that QCT may be localized at two main clusters, the first is at the dimer interface and the second at the active site like region. The clusters positions and binding energies reinforce the experimental data.