Binding of Fatty Acid Amide Amphiphiles to Bovine Serum Albumin: Role of Amide Hydrogen Bonding

Abstract

The study of protein–surfactant interactions is important because of the widespread use of surfactants in industry, medicine, and pharmaceutical fields. Sodium <i>N</i>-lauroylsarcosinate (SL-Sar) is a widely used surfactant in cosmetics, shampoos. In this paper, we studied the interactions of bovine serum albumin (BSA) with SL-Sar and sodium <i>N</i>-lauroylglycinate (SL-Gly) by use of a number of techniques, including fluorescence and circular dichroism spectroscopy and isothermal titration calorimetry. The binding strength of SL-Sar is stronger than that of structurally similar SL-Gly, which differs only by the absence of a methyl group in the amide nitrogen atom. Also, these two surfactants exhibit different binding patterns with the BSA protein. The role of the amide bond and hence the surfactant headgroup in the binding mechanism is discussed in this paper. It was observed that while SL-Sar destabilized, SL-Gly stabilized the protein structure, even at concentrations less than the critical micelle concentration (cmc) value. The thermodynamics of surfactant binding to BSA was studied by use of ITC. From the ITC results, it is concluded that three molecules of SL-Sar in contrast to only one molecule of SL-Gly bind to BSA in one set of binding sites at room temperature. However, on increasing temperature four molecules of SL-Gly bind to the BSA through H-bonding and van der Waals interactions, due to loosening of the BSA structure. In contrast, with SL-Sar the binding process is enthalpy driven, and very little structural change of BSA was observed at higher temperature