Spectroscopic studies on the gemini surfactant mediated refolding of human serum albumin

Refolding of guanidinium hydrochloride (GdCl) denatured human serum albumin (HSA) using a combination of cationic gemini surfactants; pentanediyl-α,ω-bis(cetyldimethylammonium bromide) (C₁₆H₃₃(CH₃)₂N⁺-(CH₂)₅-N⁺(CH₃)₂C₁₆H₃₃)2Br^- designated as G5 and methyl- β-cyclodextrin, is attempted in the present study. The studies were carried out in an aqueous medium (pH 7.4) using dynamic light scattering (DLS), circular dichroism (CD) and fluorescence spectroscopy. A careful study of the DLS data indicates that against the hydrodynamic radius (R_h) of 3.5nm in native human serum albumin (HSA), hydrodynamic radius after attempting refolding by simple dilution increases to 33.8nm. The large R_h values of the diluted protein sample is associated with the formation of aggregates as dilution is an aggregation prone pathway. Hydrodynamic radii equal to 5.4nm, that is very near to the native protein (3.5nm), is obtained on the sequential addition of G5 and methyl- β-cyclodextrin to the denatured protein. The results obtained from the multi-technique approach are associated with the presence of two charged head-groups and two hydrocarbon tails in the gemini surfactants resulting in very strong electrostatic and hydrophobic interactions.The present study suggests that gemini surfactants may be utilised in the protein refolding studies and may prove to be inexpensive and efficient folding agents.