Comparative effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability and activity of lysozyme

Protein interactions with surfactants are dependent on their physiochemical properties. The effect of cationic gemini surfactant hexanediyl-a,u-bis-(N-(2-hydroxyethyl)-N-methylhexadecylammonium dibromide) on the stability and activity of hen egg white lysozyme was compared with its monomeric counterpart N-(2-hyroxyethyl)-N,N-dimethylhexadecylammonium bromide at pre and post micellar concentrations. This study utilizes circular dichroism (CD), steady-state fluorescence spectroscopy, extrinsic fluorescence spectroscopy, time-resolved fluorescence spectroscopy, UV-visible spectroscopy, molecular docking and turbidity assays to resolve the conformational stability and antibacterial activity of lysozyme in the presence of surfactants. Micelles of both cationic surfactants were observed to stabilize the conformation of the protein, however, gemini was found to stabilize it in a much higher micellar concentration range. Detailed analysis of the time-resolved fluorescence spectroscopy results suggests contribution of the lifetime values of Trp62 and Trp108 to the overall conformation change of lysozyme with the increase in concentration of the respective surfactants, which is further correlated with the steady-state fluorescence and CD spectroscopy results. Furthermore, from the CD analysis it was found that the cationic single chain surfactant strongly perturbs the secondary and tertiary structure of the protein as compared to the gemini surfactant. Through docking results, it was found that the gemini surfactant binds weakly with lysozyme as compared to the single chain surfactant. Specifically, the antibacterial activity of lysozyme was found to be increased in the presence of cationic gemini surfactant, which extrapolates the use of these surfactants in pharmaceutics and industries.