Unfolding and Refolding of Bovine Serum Albumin Induced by Cetylpyridinium Bromide

Abstract

The interaction of bovine serum albumin (BSA) with cationic surfactant cetylpyridinium bromide (CPB) in aqueous solution (pH 7.00) was studied quantitatively with ultraviolet (UV)-visible, far-UV, and near-UV circular dichroism, fluorescence, small angle x-ray scattering, and nuclear magnetic resonance measurement. It was found that CPB at low and high concentrations could induce the unfolding and refolding of BSA, respectively. We suggest that in the unfolding process, there existed BSA-CPB complex with the "necklace and bead" structure in which the unfolded BSA wrapped around CPB micelles, and that the hydrophobic interaction between the complexes led to the formation of large aggregates. The aromatic headgroup of CPB interacted with the tryptophan residues of BSA, resulting in the aromatic ring stacking between BSA and CPB. During the refolding process, the BSA molecule was penetrated into the rod micelle of CPB and the hydrophobic moiety of the BSA molecule was exposed outside while its hydrophilic part was hidden inside, thereby disrupting the aromatic ring stacking.

Amino acid-based cationic gemini surfactant–protein interactions

“…The variations in the fluorescence spectra obtained by exciting the protein at 295 nm have been attributed to the presence of tryptophan residues while the changes that result from protein excitation at 280 nm are associated with both tryptophan and tyrosine residues [26,28]. As the fluorescence intensity and the wavelength of emission maximum ( max ) are sensitive to protein conformation, these parameters become important tools in probing protein folding and/or unfolding processes [20][21][22][23]50,57]. BSA has 19 Tyr residues in different domains and two Trp residues, namely Trp 134, present at the protein surface in domain I, and Trp 213, present in the hydrophobic binding pocket of the protein in domain II, that act as intrinsic fluorophores [58,59].…”

“…As the fluorescence intensity and the wavelength of emission maximum ( max ) are sensitive to protein conformation, these parameters become important tools in probing protein folding and/or unfolding processes [20][21][22][23]50,57]. BSA has 19 Tyr residues in different domains and two Trp residues, namely Trp 134, present at the protein surface in domain I, and Trp 213, present in the hydrophobic binding pocket of the protein in domain II, that act as intrinsic fluorophores [58,59]. At the excitation wavelength of 280 nm, the quenching in BSA mainly occurs from binding of the surfactant ion in the vicinity of the forementioned Trp residues [60].…”

“…Ionic surfactants are known to bind to proteins by both electrostatic (specific) and hydrophobic (cooperative) interactions leading to protein unfolding and formation of a surfactant-protein complex [16][17][18][19][20][21][22][23]. This mechanism is on the basis of their employment as denaturing agents in the extraction and purification of proteins from biological matrixes as well as on protein characterization [24,25].…”

Surfactant–Amino Acid and Surfactant–Surfactant Interactions in Aqueous Medium: a Review

“…Wool and human hair are proteinacious in nature, which on a regular basis are exposed to surfactants. The single-chain surfactants including cetyltrimethylammonium bromide (CTAB), SDS, and tertcetylphenoxypolyethoxyethanol (Triton X-100) are investigated extensively [65][66][67][68][69] and proteins with double-chain surfactants interactions are studied less. The interactions between nonionic water-soluble polymers and surfactants are of technological importance and have been the subject of intense studies over the last three decades due to their wide range of applications [70].…”

Conformational changes and sequence analysis in cellulase from Aspergillus niger with cationic surfactant

“…This strongly depends on enzyme and surfactant type, physico-chemical properties such as pH, ionic strength and temperature (Otzen 2002;Bordbar et al 2008). Therefore, several methods such as: microcalorimetry, circular dichroism (CD), fluorescence and potentiometry were used to evaluate this system (Bordbar et al 2008;Sun et al 2005).…”