Non-ionic Detergent-Assisted Refolding of Protein from Protein-SDS Complex

Refolding of protein from denatured structure caused by sodium dodecyl sulfate (SDS) was examined using agarose native gel electrophoresis and circular dichroism (CD). Refolding of protein from SDS complex was induced with the addition of non-ionic and zwitterionic detergents followed by agarose native gel electrophoresis. The native gel electrophoresis was done without both SDS and non-ionic detergents in the agarose gel and running buffer. The electrophoretic mobility of bovine serum albumin (BSA) drastically increased with the addition of 1% SDS to the samples indicative of SDS-BSA complex formation. The SDS-denatured BSA returned to the native mobility by the addition of non-ionic Tween 20 and Triton X-100 and zwitterionic CHAPS as a function of detergent concentration. Refolding, at least partially, was confirmed by CD, which was done in the presence of both SDS and non-ionic detergents, a condition different from the native gel electrophoresis done in their absence. When BSA was denatured by both 1% SDS and a disulfide-reducing dithiothreitol, even 10% Tween 20 was insufficient to restore the native BSA mobility on agarose native gel electrophoresis. When BSA was denatured by 1% Sarkosyl and sodium lauroyl-glutamate, Tween 20 restored the native structure at Tween 20 concentration lower than the Tween 20 concentration used for SDS denaturation. A similar refolding by non-ionic detergents was also observed for a rabbit monoclonal IgG, but not for lysozyme. The results with lysozyme suggest strong SDS binding and difficulty in dissociating the bound SDS by non-ionic detergents due to high isoelectric point of the protein and thereby more SDS binding.