| The interaction of a light-responsive azobenzene-based surfactant ("azoTAB") with proteins has been investigated as a means to photoreversibly control protein structure, dynamics, and function. AzoTAB undergoes a reversible photoisomeriztion upon exposure to appropriate wavelength of light, with the visible-light, trans isomer being more hydrophobic and, thus, inducing a greater degree of protein unfolding than the UV-light, cis form. AzoTAB is found to induce triggered and localized protein unfolding, measured directly in solution with small-angle neutron scattering (SANS) experiments, and to further influence the biological function and dynamics of proteins. For example, the relationship between photoreversible changes in secondary and tertiary structure of BSA, found to exist as one of three discrete forms depending on the azoTAB concentration, has been examined. Similarly, photo-control of the form-function relationship of lysozyme has been studied. With azoTAB in the trans form under visible light a partially-unfolded intermediate conformation of lysozyme with an exposed active site was found, while lysozyme was observed to refolded to a native-like structure upon UV illumination. In addition, enhanced dynamics within the partially-unfolded form of lysozyme were observed with neutron spin echo (NSE) measurements and thought to contribute to a nearly 8-fold enhancement in the enzyme activity compared to the native state. Combined, these results provide insight into a unique light-based method of controlling the complete structure-dynamics-function relationship of proteins. |
