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 c onformational substates of the protein. These conformational trajector ies may differ in the ground and excited states. The molecule constant structural changes exposes the fluorescent protein residues to contin uously mutating environments in a predetermined sequence given by the molecule conformational path. The absorption extinction coefficient an d the emission decay rate of a given fluorescent residue, dependent up on the instantaneous localized environment of the residue, are modulat ed by the conformational dynamics of the molecule. A simple harmonic c onformational trajectory describes the behavior of traditional, time i nvariant, fluorescence lifetime distributions with temperature. The li fetime distribution describes at any given time the distribution of ex cited residues in the protein conformational space. Consequently, dyna mic conformational trajectories require the use of time dependent life time distributions. The evolution of uniform lifetime distributions mo dulated by harmonic conformational trajectories are illustrated. The r esults presented here open the way to the description of complex confo rmational dynamics in terms of structural harmonic fluctuations.