Protein-surfactant interactions

Abstract: Protein-surfactant interactions in aqueous media have been investigated. The globular proteins lysozyme and bovine serum albumin (BSA) served as model proteins. Several ionic and non-ionic surfactants were used.Fluorescence probe measurements showed that at low sodium dodecyl sulfate (SDS) concentration (< 0.1 M) one micelle-like SDS cluster is bound to lysozyme. From dynamic light scattering (DLS) results it was observed that lysozyme in the complex does not correspond to the fully unfolded protein. At high SDS concentration (> 0.1 M) one compact and one more extended lysozyme-SDS complex coexist.The influence of surfactant alkyl chain length and headgroup on BSA-surfactant complex formation was investigated. In these studies, binding isotherms were determined by nuclear magnetic resonance (NMR), DLS was used to measure the hydrodynamic radii of the complexes and the size of the micelle-like aggregates on BSA was determined using fluorescence probe methods.It was observed from fluorescence measurements that the number of bound SDS molecules does not depend on the presence of the disulfide bridges. Reduced proteins wrap more efficiently around the micelle-like structures, resulting in somewhat smaller complexes, as observed with DLS.Concentrated BSA-SDS solutions and the corresponding heat-set gels were investigated using DLS and fluorescence probe methods. Correlation lengths in the gel were determined and it was concluded that SDS forms micelle-like aggregates on BSA in concentrated solution and gel phase. The gel region in the ternary phase diagram BSA-SDS-3.1 mM NaN3 has been determined at room temperature.