THE EFFECT OF HARMONIC CONFORMATIONAL TRAJECTORIES ON PROTEIN FLUORESCENCE AND LIFETIME DISTRIBUTIONS

Proteins change their structure constantly due to their conformational flexibility and dynamic nature. The structure of the molecule follows a trajectory in conformational space determined by the hierarchy of conformational substates of the protein. These conformational trajectories may differ in the ground and excited states. The molecule constant structural changes exposes the fluorescent protein residues to continuously mutating environments in a predetermined sequence given by the molecule conformational path. The absorption extinction coefficient and the emission decay rate of a given fluorescent residue, dependent upon the instantaneous localized environment of the residue, are modulated by the conformational dynamics of the molecule. A simple harmonic conformational trajectory describes the behavior of traditional, time invariant, fluorescence lifetime distributions with temperature. The lifetime distribution describes at any given time the distribution of excited residues in the protein conformational space. Consequently, dynamic conformational trajectories require the use of time dependent lifetime distributions. The evolution of uniform lifetime distributions modulated by harmonic conformational trajectories are illustrated. The results presented here open the way to the description of complex conformational dynamics in terms of structural harmonic fluctuations.