Deciphering active site strain

Strain at the active site of proteins has been invoked to understand processes ranging from enzyme catalysis to energy storage in transient intermediate states during the first steps of vision. We are developing Raman Optical Activity (ROA), based on differences between Raman scatter using left- versus right-circularly polarized light, as an approach to quantitatively determine dihedral angle distortions at the active site of chromophoric proteins. Previously, we showed that pre-resonance conditions offer a unique spectral window to obtain structurally informative spectroscopic data, and reported that the ROA amplitude of selected vibrational modes can function as spectroscopic rulers for specific active site dihedral angles. In this work, quantum chemical calculations form an essential bridge connecting available crystallographic data with vibrational spectra. Currently, we are developing tools that can determine if high-resolution features of chromophoric active sites reported in crystal structures are viable structural models based on their ability to reproduce observed Raman data.