(52g) Reversible Changes in Protein Secondary Structure with Light Using Photoresponsive Surfactants

The ability to use simple light illumination to reversibly control protein folding will be discussed, with particular emphasis on light-induced changes in protein secondary structure (a-helices, b-sheet, etc.). This novel method utilizes photoresponsive azobenzene surfactants as a means to induce reversible conformation changes in proteins. The surfactant undergoes a photoisomerization upon exposure to the appropriate wavelength of light; with the visible-light (trans) form of the surfactant being more hydrophobic than the UV-light (cis) form. As a consequence, the surfactant can reversibly bind to the hydrophobic domains of proteins, leading to photocontrol of protein folding, demonstrated in this work using a range of proteins (e.g., BSA, lysozyme, bacteriorhodopsin, etc.). Several experimental techniques will be employed to study these photosurfactant-protein systems, with particular emphasis on Fourier transform infrared spectroscopy (FTIR) as a means of quantifying the reversible changes in secondary structure elements, providing protein conformational information and insight into the folding and unfolding mechanisms of proteins. Light-induced changes of protein secondary structure will be compared to similar changes in protein tertiary structure obtained from relatively high-resolution in vitro conformations determined with small-angle neutron scattering data. The process is shown to be remarkably reversible. Throughout several unfolded-refolded cycles induced by light, both the secondary and tertiary structures of the light-denatured and light-refolded states are independent of cycle number.