Studies of interaction between ergosta-4,6,8(14),22-tetraen-3-one (Ergone) and human serum albumin by molecular spectroscopy and modeling

Abstract

Our previous experimental results have shown that ergosta-4,6,8(14),22- tetraen-3-one (ergone) is one of the main bioactive components of Polyporus umbellatus. The efficacy of ergone binding to human serum albumin (HSA) is critical for pharmacokinetic behavior of ergone. The interactions between ergone and HSA under simulative physiological conditions were investigated by the methods of fluorescence spectroscopy, absorption and circular dichroism spectroscopy. Fluorescence data revealed that the fluorescence quenching of HSA by ergone was the result of the formation of the ergone-HSA complex. According to the modified Stern-Volmer equation, the binding constants (Ka) between ergone and HSA were determined. The thermodynamic parameters, enthalpy change (δH) and entropy change (δS) for the reaction were calculated to be 0.989 kJ mol-1 and 11.214 J mol-1 K-1, indicating that the hydrogen bonds and hydrophobic interactions played a dominant role in the binding of ergone to HSA. The conformational investigation showed that the presence of ergone decreased the α-helical content of HSA and induced the slight unfolding of the polypeptides of protein. Furthermore, displacement experiments using warfarin and ibuprofen indicated that ergone could bind to site I of HSA, which was also in agreement with the results of the molecular modeling.