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, [C8mim][C12OSO3], in aqueous medium at pH 4.8. Adsorption and binding isotherms determined from tensiometry and isothermal titration calorimetry indicated that [C8mim][C12OSO3] interacts with cellulase distinctly at the three critical concentrations, viz., aggregation, C1, saturation, C2, and vesicular, C3. Fluorescence (at λex = 280 nm), far UV-circular dichroism spectra, and dynamic light scattering results have shown that [C8mim][C12OSO3] alters the tertiary and secondary structure of cellulase with a slight initial unfolding in the monomeric regime (up to C1), refolding in the aggregation regime (up to C2), and unfolding in the shared aggregation regimes (below C3) 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 [C8mim][C12OSO3] as a potential alternative of mixed micelles or nonionic surfactants for cellulase stabilization in detergent industries.