Protein function is known to be greatly influenced by its conformation. However, in the past couple of decades supporting experimental and theoretical evidence presents a scenario in which protein dynamics are also correlated with protein function. As a result, correlation between conformation and dynamics may be significant in some protein systems and introducing a model to describe such correlations can be beneficial in modeling protein function. Thus, the first specific aim is to formulate a dynamical model which incorporates the complexity of protein structure. The second specific aim is to test the model by observing the time resolved fluorescence of the single tryptophan residue in human superoxide dismutase (HSOD). HSOD reduces radical oxygen and releases hydrogen peroxide in the process. The protein dynamics can be studied by performing temperature dependent time resolved fluorescence experiments. Dynamic correlations to protein conformation can be investigated by performing denaturant dependent time resolved fluorescence experiments. The third specific aim is to correlate the model with the function of HSOD. The theoretical proposal to model the protein dynamics of HSOD is a bifurcating ultrametric distributed system (BUDS). The complexity of protein structure is contained in BUDS through a hierarchy of conformational substates. Protein dynamics are reflected in BUDS by the interconversions of the protein system between conformational substates. Substate interconversion involves the thermal activation of the system over a hierarchy of free energy barriers. Experimental work on the time resolved fluorescence of HSOD will be done by multi-frequency phase fluorometry at the Laboratory for Fluorescence Dynamics at the University of Illinois, Urbana-Champaign. Fluorescence experiments of HSOD will be done over a wide temperature and denaturant range. In addition, circular dichroism (CD) experiments of HSOD will be done as a function of denaturant concentration and temperature to reveal any changes in the protein's secondary structure. Preliminary CD experiments of HSOD confirm that its secondary structure progressively unfolds as denaturant concentration increases. Preliminary fluorescence experiments of HSOD under various thermal and denaturant conditions reveal that 1) the time resolved fluorescence of native and denatured HSOD is best described by a distribution of fluorescence lifetimes, 2) the width of the fluorescence lifetime distribution of both native and denatured HSOD increases with decreasing temperature, 3) the width of the fluorescence lifetime distribution as a function of denaturant concentration displays a maximum which is not coincident with the fully denatured form of HSOD, 4)the width of the fluorescence lifetime distribution of denatured HSOD is greater than that of native HSOD.
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