Stabilizing effect of quercetin upon bovine serum albumin as a model protein

Quercetin (QCT), an emerging class of flavonoid known for antioxidant and anti-inflammatory activities, has been studied for its protein stabilizing effect. After demonstrating ethanol (EtOH) - induced structural changes in bovine serum albumin (BSA), the stabilizing effect of QCT was studied using fluorescence, circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopic techniques. Morphological changes were examined using atomic force microscopy (AFM). EtOH triggered blue shift in fluorescence spectra of BSA and its intensity increased at higher percentage of alcohol. A reversal in this trend was recorded in the presence of QCT. This was interpreted as anti-amyloidogenic effect emanating from the binding of QCT to hydrophobic pockets of BSA. The value of binding constant (1.25 x 10⁶ M^-1; 298 K) is suggestive of strong binding affinity of QCT for BSA. The mode of QCT-induced fluorescence quenching was found to be mixed in nature. CD spectra showed that the protein conformation was altered and traces of alpha helix disappeared in the presence of EtOH. Contrarily, disruptive effect of EtOH was not visible upon incorporating QCT. This was further verifiable form the thermal CD data, which showed an upshift in the denaturation temperature of BSA. The data of thioflavin T assay and AFM further substantiated the protective effect of QCT.