Conformational change of protein sodium dodecylsulfate complexes in solution: A study of dynamic light scattering

Abstract

The binding of an ionic detergent [sodium dodecyl sulfate (SDS)] to two proteins [bovine serum albumin (BSA) and ovalbumin (OA)] has been studied by dynamic light scattering to determine the changes of the hydrodynamic size and shape of the proteins as a function of binding. This study has been correlated to a previous viscosity study (Ref. 1) in which the increase in the effective hydrodynamic radius of the detergent–protein complex as the gram ratio of detergent to protein increases has been interpreted as the unfolding of the protein as a direct result of the disruption of the intramolecular hydrophobic associations in the proteins by the SDS molecules. At the maximum binding, the BSA–SDS complex exhibits a hydrodynamic radius of 72 Å while the effective size of the native BSA is 27 Å. The OA–SDS complex has an effective hydrodynamic radius of 64 Å at the maximum binding while that of native OA is 22 Å. The dynamic light scattering experiments allow us to detect the presence of two different size species in the solution, the SDS micelles and the unfolded proteins combined with SDS. However, the shape of the protein–SDS complex at maximum binding cannot be definitely determined from the present measurements alone.