Proteins as Surfactant Enhancers for Environmental and Industrial Applications

Introduction:

Studies of protein-surfactant interactions go back about a century, being inspired by broad practical implications. There is extensive literature on this topic. However, most of the publications concentrateon the effect of surfactants on proteins, such as the unfolding and refolding of the protein coil, and the application of surfactants in isolation and purification of proteins, especially those incorporated into biological membranes. 

For water-soluble proteins, interactions with surfactants were broadly split up into two regions: below and above the surfactant’s critical micelle concentration (CMC). With anionic surfactants (such as sodium lauryl sulfate) the binding to a protein (such as lysozyme) starts before the surfactant’s CMC is achieved, leading to a plateau in the Gibbs isotherm at 15 to 20 surfactant molecules bound to each protein globule.

After the CMC has been surpassed, further steep growth of binding was found. Below the surfactant’s CMC,water-soluble protein may undergo a series of conformational changes as it is binding an increasing numbers of ionic surfactant molecules. The two major and discrete events in the perturbation of protein structure were briefly summed up as tertiary structure unfolding in the sub-micellar zone, and chain expansion in the micellar range of ionic surfactant concentrations. In contrast, only very weak interactions with non-ionic surfactants were noticed in this sub-micellar concentration range.