Secondary structural changes in guanidinium hydrochloride denatured mammalian serum albumins and protective effect of small amounts of cationic gemini surfactant pentanediyl-α,ω-bis(cetyldimethylammonium bromide) and methyl-β-cyclodextrin: A spectroscopic study

Abstract

In the present study the cationic gemini surfactant assisted refolding of guanidinium hydrochloride (GdCl) denatured mammalian serum albumins viz. sheep serum albumin (SSA), rat serum albumin (RSA) and porcine serum albumin (PSA) 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 in the artificial chaperone assisted two step method, is attempted. The studies were carried out in an aqueous medium (pH 7.4) using dynamic light scattering (DLS), circular dichroism (CD), and fluorescence spectroscopy. A perusal of DLS data indicates that against the native hydrodynamic radius (Rh) of 4.3nm in SSA, 3.9nm in PSA and 3.5nm in RSA, the Rh of the said proteins, when refolding is attempted by simple dilution, increases to 21.7nm, 36.6nm and 37.2nm, respectively. Hydrodynamic radii very near to the native protein, i.e., 4.0nm, 4.1nm and 4.4nm for RSA, PSA and SSA respectively, is obtained on the sequential addition of G5 and methyl-β-cyclodextrin to the denatured protein. Circular dichroism studies corroborate with the DLS data. The results obtained from the multi-technique approach are ascribed to the presence of two charged head-groups and two hydrocarbon tails in the gemini surfactants resulting in a very strong electrostatic and hydrophobic interactions. Based on the present study it is suggested that the gemini surfactants may be utilized in the protein refolding studies and thus may address one of the most pressing demand of biotechnology industry for the development of efficient and inexpensive folding aides.