(384d) Photo-Control of Protein Folding, Dynamics, and Association

Lee, Jr., C. T. - Presenter, University of Southern California
Hamill, A. C. - Presenter, University of Southern California
Wang, S. - Presenter, University of Southern California

Proteins are the workhorses of biology. Beginning as chains of specific combinations of amino acids, proteins fold due to these amino acids having differing degrees of affinity for or aversion to water. It is this seemingly simple folding event, and the resulting shape that the protein adopts in solution, often called the native state, which gives rise to a functional protein. However, proteins are not static entities and instead regularly undergo conformational changes to intermediately-folded or associated states during the course of activity, particularly upon interaction with other molecules. As such, information on the native state alone will not provide complete understanding of the form-dynamics-function relationship. Instead, precise knowledge of the structure and dynamics of the partially-folded or oligomeric states that form in response to various stimuli is required. Thus, to properly investigate this phenomenon necessitates two complementary approaches: (1) a means to induce changes in protein structure in a controlled and preferably reversible manner, and (2) a method to determine the conformation of non-native proteins at relatively high resolution. To achieve these tandem goals, we have developed two novel techniques, namely the interaction of proteins with photoresponsive surfactants to allow photoreversible control of protein structure, and the use of small-angle neutron scattering (SANS) to study non-native protein conformations in response to photosurfactant and light. We advance the argument that SANS has the potential to be the technique of choice to study in vitro protein conformations, including novel structural characterization of difficult-to-crystallize states such as partially-folded proteins in non-native conformations, supramolecular complexes undergoing self- or hetero-aggregation, proteins in action or systems that undergo domain motions upon activation, and membrane proteins dispersed in solution with surfactants or lipid bilayers. The specific case of photo-reversible control of amyloid protein association will be examined, beginning with the structure of the initial-formed protein oligomers all the way to complete fibril formation. In addition, we will describe novel neutron spin echo (NSE) measurements of protein internal dynamics on the nanosecond time scale and nanosecond length scale. A partially-unfolded form of lysozyme is found to exhibit a 10-fold increase in enzyme activity relative to the native state. While at first it may seem counterintuitive that an unfolded enzyme would be more active than the native state, the NSE measurements reveal a dramatic increase in domain motions that lead to this ?superactivity?. Thus, photo-control of the complete form-dynamics-function relationship in enzymes is demonstrated.