Physicochemical nature of sodium dodecyl sulfate interactions with bovine serum albumin revealed by interdisciplinary approaches

Abstract

To rigorously characterize the interactions of sodium dodecyl sulfate (SDS) with bovine serum albumin (BSA) a set of experimental methods, namely isothermal titration calorimetry, conductometric titration, steady-state fluorescence spectroscopy, differential scanning calorimetry and circular dichroism spectroscopy, supported by in silico analysis have been applied. The influence of pH and temperature on the binding mode has been revealed. At a low molar ratio of SDS to BSA up to ca. 16:1, there are at least two structurally distinct binding sites in BSA. The formation of SDS-BSA complexes is an enthalpy-driven process in which the van der Waals interactions play a crucial role. The first binding site, located close to the Trp-134 residue within the sub-domain IA, is pH-independent and binds two molecules of SDS per one molecule of BSA whereas the total number of SDS molecules bound to the second site of albumin is affected by temperature and pH. The saturation of the first binding site of BSA (ca. 0.009 mg of SDS per 1 mg of BSA) is sufficient to thermally stabilize the helical conformation of BSA. The presented results have important structural and thermodynamic implications to understand the influence of a widely used anionic surfactant on globular protein functionality in modern branches of chemistry.