Structural and Functional Stability of Cellulase in Aqueous-Biamphiphilic Ionic Liquid Surfactant Solution

In order to explore the potential of a biamphiphilic ionic liquid surfactant as an enzyme stabilizer in detergents, we have investigated the structural and functional stability of cellulase upon interaction with 3-methyl-1-octylimidazolium dodecylsulfate, [C(8)mim][C12OSO3], in aqueous medium at pH 4.8. Adsorption and binding isotherms determined from tensiometry and isothermal titration calorirnetry indicated that [C(8)mim][C12OSO3] interacts with cellulase distinctly at the three critical concentrations, viz., aggregation, C-1, saturation, C-2, and vesicular, C-3. Fluorescence (at lambda(ex) = 280 nm), far UV-circular dichroism spectra, and dynamic light scattering results have shown that [C(8)mim][C12OSO3] alters the tertiary and secondary structure of cellulase with a slight initial unfolding in the monomeric regime (up to C-1), refolding in the aggregation regime (up to C-2), and unfolding in the shared aggregation regimes (below C-3) and stabilizes the altered conformation in the post-vesicular regime with an overall variation of hydrodynamic diameter from 4.12 to 7.19 nm. A dinitrosalicylic acid sugar assay test showed excellent functional stability of cellulase with an activity of >= 1 unit/mg in all the concentration regimes. A very good surface activity (J. Phys. Chem. B 2012, 116, 14363) complied by the present results vindicates the candidature of [C(8)mim][C12OSO3] as a potential alternative of mixed micelles or nonionic surfactants for cellulase stabilization in detergent industries.