Thermodynamic analysis of serum albumin denaturation by sodium dodecyl sulfate

Abstract

Binding of variable amounts of sodium dodecyl sulfate (SDS) to bovine serum albumin (BSA) may be followed by analytical ultracentrifugation. The molar masses of the protein-surfactant complexes obtained from sedimentation equilibria allow binding isotherms to be established. UV absorption spectroscopy, fluorescence and circular dichroism are used for probing the conformational stability of proteins upon addition of surfactants, similar to the approaches used for denaturation by strong chaotropic reagents or heat. Measurements allow the determination of the equilibrium constant and the free energy, ΔG, for the transition from the folded (native) to the unfolded (denatured) state. ΔG at 25 °C in the absence of a surfactant or denaturant may be taken as a measure for the conformational stability of a protein. Though the results depend on the validity of certain assumptions regarding the folding/unfolding mechanism, as well as the evaluation method and the experimental conditions, the thermodynamics of surfactant-induced unfolding may be estimated and compared to the results of similar binding and unfolding experiments with other denaturants. The data presented in this work refer to BSA as a model. The results show diminished DG values for SDS-induced denaturation, compared to unfolding experiments with chaotropic denaturants or heat denaturation.