Protein dynamics studied by room temperature phosphorescence spectroscopy

Proteins are fundamentally dynamic entities, undergoing conformational changes in response to interaction with ligands during the performance of their biological function, or during the process of folding into their final, biologically active, structures. Advanced transient laser spectroscopy techniques based on intrinsic chromophores provides a powerful means to study these changes. Specifically, time-resolved phosphorescence of tryptophan (Trp) provides a means to observe the dynamics associated with different regions of the protein surrounding the emitting Trp residue. Using these methodologies, we have been able to demonstrate intrinsic equilibrium conformational heterogeneity in proteins, and have been able to study, in real time, slow events in the unfolding and refolding of these macromolecules. In addition, we have used circularly polarized phosphorescence to report on the chirality of the excited triplet state of Trp, which enables us to resolve two or more phosphorescing Trps with similar lifetimes. We briefly summarize some of these results, and present new room temperature phosphorescence (RTP) data characterizing the trifluoroethanol (TFE) induced (beta) -sheet to (alpha) -helix transition in the bovine milk protein, (beta) -lactoglobulin A