Twin-tailed surfactant induced conformational changes in bovine serum albumin: a detailed spectroscopic and physicochemical study

Abstract

The interactions of a twin-tailed anionic surfactant sodium bis-2-ethylhexyl sulfosuccinate (AOT) and cationic surfactant ditetradecyldimethylammonium bromide (DTDAB) with bovine serum albumin (BSA) has been examined using various spectroscopic and physicochemical techniques such as tensiometry, steady-state fluorescence, potentiometry and isothermal titration calorimetry (ITC). The interactional behavior of the surfactants with BSA at the air–solution interface which depends upon the nature of the surfactant was examined and is discussed in detail. Steady-state fluorescence, and potentiometry combined with ITC measurements provide vital insights into the binding mechanism of the surfactants with BSA. An enhancement in the intrinsic fluorescence intensity and a strong exothermic enthalpy change at low concentrations of AOT demonstrated the crosslinking of AOT monomers between a group of non-polar residues and a positively charged residue located on different helical loops of BSA. The quenching of the intrinsic fluorescence intensity and endothermic enthalpy changes were observed over the whole of the concentration range of DTDAB that was studied indicating powerful interactions between them. The synchronous fluorescence spectra revealed the conformational changes in the peptide backbone of BSA and the altered environment of tryptophan and tyrosine residues. The binding isotherms obtained from intrinsic fluorescence spectroscopy as well as from potentiometry were analyzed using Scatchard plots to obtain insights into the binding mechanism and to evaluate the binding constants and the number of binding sites.