Assessing the interaction of Hecamegs with Bovine Serum Albumin and its effect on protein conformation: A spectroscopic study

Abstract

Interaction of the nonionic surfactant Hecamegs with the plasma protein Bovine Serum Albumin (BSA), and its effect on protein conformation,has been studied using spectroscopic techniques such as steady-state and time-resolved fluorescence and circular dichroism. A weak interaction of the surfactant with BSA is reflected by changes in the intrinsic fluorescence of BSA in either steady-state or time-resolved measurements. The fluorescence intensity data allowed us to determine the corresponding binding curve, which suggests a sequential binding mechanism, in which the surfactant first occupies the hydrophobic sites of the inner protein cavity and then,condenses onto the surface hydrophobicsites of BSA via a cooperative mechanism.Additional fluorescence data obtained by synchronous,three-dimensional and anisotropy experiments show that the surfactant mainly interacts with the tryptophan residues of BSA,which seem to experience motional restriction as a result of this interaction.Time-resolved fluorescence data,which were analyzed using the modified Stern–Volmer equation,also support the above mechanism.Finally,far-UV circular dichroism studies indicated that the secondary structure of the protein remains almost unaltered even for BSA to surfactant molar ratio as high as 1 to100.