Effect of β-CD on refolding dynamics of the unfolded and reduced states of human serum albumin

The anionic surfactant, sodium dodecyl sulfate (SDS), unfolds the circulatory protein human serum albumin (HSA) and binds to it in three distinct stages. The structural integrity rendered by the seventeen disulfide bridges inherently present in HSA, does not make the protein behave as an extended polymer upon SDS treatment. However, when this unfolded protein is subjected to β-cyclodextrin (β-CD), it regains back a substantial portion of its secondary structure. The behavior of the reduced state of the protein, which was achieved by treatment with dithiothretol, is totally different from that of the unfolded state; on addition of β-CD to this reduced state, the protein loses its structure further. Using steady-state and time-resolved spectroscopic analyses, these unfolded and reduced states of the protein, when subjected to β-CD, have been characterized. The mechanism of refolding of the unfolded state has been ascribed to the removal of the bound SDS molecules by β-CD and the reversible unfolding and refolding pathways.