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 between adjacent peptide bonds. 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 coordinate that connects secondary structure conformations. The psi angle coordinate is the most important reaction coordinate necessary to understand mechanism(s) of protein folding. We have also discovered an analogous correlation for the primary amide sidechain of Gln. This allows us to monitor the hydrogen bonding and structure of this sidechain.
We examine the details of peptide folding conformation dynamics with laser T-jumps where the water temperature is elevated by an 1.9 mM IR nsec laser pulse and we monitor the ~200 nm UV Raman spectrum as a function of time. These spectra show the time evolution of conformation. We will discuss the role of salts on stabilizing conformations in solution
Sanford A. Asher, David Punihaole, Elizabeth M. Dahlburg, Ryan S. Jakubek, and Zhenmin Hong, "UV resonance Raman spectroscopic studies of protein structure and dynamics
(Conference Presentation)," Proc. SPIE 9926, UV and Higher Energy Photonics: From Materials to Applications, 992602 (Presented at SPIE Nanoscience + Engineering: August 28, 2016; Published: 11 November 2016); https://doi.org/10.1117/12.2237046.5161498110001.
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