Fluorescence spectra, quantum yields and lifetimes have often been used as predictors of the location of a fluorophore in the protein matrix. The implicit assumption in the use of fluorescence data in this manner has been that water is the major determinant of fluorescence emission properties especially of spectral position. Molecular graphics data coupled with fluorescence data show that there is no simple way to correlate fluorescence properties with either location of the fluorophore in the protein matrix or accessibility of water to the fluorophore. We propose now to extend the studies on protein structure-fluorescence correlations by performing extensive measurements of fluorescence properties and calculations of molecular electrostatic potentials of the tryptophan environs and using molecular graphics techniques to depict environs and electrostatic potential profiles. We will study proteins containing single tryptophan residues primarily, but will in some instances also study proteins with multiple fluorophores where the fluorescence of each emitter can be resolved. An especial effort will be made to determine if radiative lifetimes provide the most meaningful decay parameter for evaluating environmental effects on protein fluorescence. Environmental effects will, in turn, be assessed by measurements of apparent dipolar relaxation rates and time resolved emission spectra at room temperature and in the ultracold. Most proteins to be studied will be of known crystal structure. We hope, thereby, to verify the roles of amino acid sidechains, of other groups in the protein matrix capable of forming exciplexes or of quenching and of water accessibility in determining the fluorescence properties evinced. The molecular graphics data will also allow depictions of the intraprotein volume available to a fluorophore for movement. Time resolved fluorescence anisotropy measurements will be used to verify the rate and extent of motion of the fluorophores independent of whole protein rotation in the picosecond to nanosecond time domain. We will try to correlate oxygen quenching of protein fluorescence with the packing density around tryptophan moieties. An attempt will be made to correlate the experimental data and the molecular graphics depictions with results from molecular dynamics calculations as the latter become available.
Showing the most recent 10 out of 67 publications
