Unfolding of human serum albumin by gemini and single-chain surfactants: A comparative study

The interactions of human serum albumin (HSA) with four cationic gemini surfactants and four single chain surfactants have been investigated from the measurements of fluorescence spectroscopy, dynamic lights scattering (DLS), zeta potential, and circular dichroism (CD). The fluorescence results show the binding strength of surfactants to HSA, along with the blue shift under the maximum emission wavelength (lambda(max)) which is sensitive to the protein conformations. It has been found that the hydrodynamic diameters of the protein aggregates are enlarged and the electrokinetic potentials of them get positive with increasing the concentration of the surfactants. The conformational transformation of the secondary structures of surfactant-HSA aggregates has been confirmed through the quantitative analysis of the CD spectra. The isothermal titration microcalorimetry (ITC) has been employed to further analyze the binding process of single-chain surfactants to HSA. The comprehensive results obtained from various approaches have shown that both hydrophobic and electrostatic interactions are present in the cationic surfactant-HSA systems. Compared with the corresponding single-chain surfactants, the gemini ones have much stronger binding ability to induce the unfolding of HSA. These investigations on the interactions between HSA and surfactants with the altered chain architecture in different concentration regimes can facilitate the application of surfactant-protein systems in pharmaceutical, biotechnology and related fields. (C) 2016 Elsevier B.V. All rights reserved.