Effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability and esterase activity of human serum albumin

The binding effect of gemini surfactant, hexanediyl-alpha,omega-bis-(N-(2-hydroxyethyl)-N-methylhexadecylammonium bromide) (16-6-16 MEA) and its monomeric counterpart N-(2-hyroxyethyl)-N,N-dimethylhexadecylammonium bromide (16-MEA) on the structure and esterase like activity of human serum albumin (HSA) was unravelled by using UV-visible, fluorescence, three dimensional fluorescence, time resolved fluorescence and circular dichroism techniques in combination with molecular docking and molecular dynamic simulation methods. Fluorescence quenching mechanism was employed to estimate the Stern-Volmer quenching constants, 4, and the corresponding thermodynamic parameters like Delta G, Delta S and Delta H for HSA-16 MEA/16-6-16 MEA systems. The results showed the static quenching mechanism and spontaneous binding of 16 MEA/16-6-16 MEA with HSA. In addition to other interactions, the hydrophobic interaction (which is more effective in case gemini surfactant) plays major role in the process of binding of both the surfactants with HSA. Synchronous fluorescence reveals that there is a slight effect of 16 MEA/16-6-16 MEA on the fluorescence intensity of tyrosine but a significant effect on tryptophan. UV-visible results obtained, suggest the complex formation between HSA and 16MEA/16-6-16 MEA through static quenching mechanism. Circular dichroism results confirmed that the decrease in the alpha-helical content of HSA is more on interaction with 16-6-16 MEA as compared to 16 MEA. In addition, the esterase activity of HSA was also done, which was found to decrease in presence of both 16 MEA and 16-6-16 MEA. Additionally, we also utilized computational approaches for deep insight into the binding of 16 MEA/16-6-16 MEA with HSA and the results well matched with our experimental results. (C) 2018 Elsevier B.V. All rights reserved.