Probing the interaction between human serum albumin and the sodium dodecyl sulphate with fluorescence correlation spectroscopy

The denaturation of human serum albumin (HSA) upon interaction with the surfactant sodium dodecyl sulphate (SDS) was examined by measuring the diffusion time of fluorophore (RITC) tagged HSA under near single-molecule conditions using fluorescence correlation spectroscopy. The diffusion time shows four distinct regions as a function of SDS concentration, which corresponds to (I) opening of the tertiary structure, (II) non-specific SDS aggregation, (III) opening of the secondary structure, and (IV) aggregation of SDS around the secondary structure. Diffusion time increases from 383 µs for the free protein to 1002 µs for the SDS bound protein, which leads to an effective increase in the hydrodynamic radius by a factor of about 2.6.