Photocontrol of protein conformation and enzyme activity in the presence of light-responsive surfactants

Photo-responsive surfactants along with light illumination have been utilized to approach a novel light-based technique to reversibly control dynamic-form-function relationship of enzymes. The photosurfactant, namely azoTAB, undergoes a reversible photoisomerization from the relatively-hydrophobic trans isomer under visible light to the relatively-hydrophilic cis isomer upon UV illumination. The more hydrophobic trans form of the surfactant has a higher binding affinity for proteins and, hence, induces a greater degree of protein unfolding compared to the cis isomer. Therefore, the photoreversibility of the surfactant provide the ability to reversibly control enzyme-surfactant interactions. Photocontrol of the structure and function of carbonic anhydrase has been investigated. Carbonic anhydrase dramatically unfolds in the presence of the trans-surfactant while only a small degree of unfolding is observed upon UV illumination. Consequently, the enzyme is completely inactivated in the presence of the trans-surfactant, but performs some of its original function under UV light, providing a photoreversible on/off switch of enzyme activity. Photocontrol of the dynamic-form-function relationship of RNase A and lysozyme has also been studied, indicating that both enzymes undergo partial unfolding and exhibit superactivity in the presence of the trans-surfactant. However both protein unfolding and superactivity is reversed back to a native-like condition with UV illumination. One of the advanced applications of the photosurfactant is to dissociate enzyme/inhibitor complexes in order to reactivate enzymes. The effect of azoTAB on RNase A/RI complex has been examined. RI is a strong inhibitor of RNase A and RNase/RI is known as one of the tightest enzyme/inhibitor complexes. In the presence of the trans-surfactant, RNase/RI complex dissociates, leading to RNase A reactivity. The complex dissociation occurs through protein unfolding, mainly RI unfolding. Therefore, RNase inhibition can be reversed to native-like activity upon addition of the trans-surfactant. Altogether, photo-responsive surfactants combined with light illumination can be used as a mean to reversibly photocontrol the structure, dynamic, and function of enzymes, as well as to photocontrol of enzyme/inhibitor complexes.