We developed a powerful method to follow the evolution of secondary structure in peptides and proteins.  UV Raman excitation into the ~200 nm peptide bond electronic transitions enhance peptide bond amide vibrations of the backbone. A particular band (the amide III3) reports on the Ramachandran psi angle and peptide bond hydrogen bonding.  This band is Raman scattered independently by each peptide bond with insignificant coupling.  Isotope editing of a peptide bond (by replacing the Calpha- H with Calpha- D) allows us to determine the frequency of individual peptide bonds within a peptide or protein to yield their psi angles.  Consideration of the Boltzmann equilibria allows us to determine the psi angle Gibbs free energy landscape along the psi (un)folding that connects secondary structure conformations.  The psi angle coordinate is the most important reaction coordinate necessary to understand mechanism(s) of protein folding.

UV resonance Raman measurement of the energy landscape for  protein and peptide folding

243rd National Meeting (2012)

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