We use tools including semi-synthesis and post-translational modification of cysteines to incorporate unique infra-red chromophores for use as probes of the organized interior of proteins. We calibrate the sensitivity of these vibrations to electric fields using vibrational Stark effect spectroscopy and use this calibration to quantitatively interpret the electric field environment experienced by the probe. We are currently employing this method to quantify the contribution of these electric fields to catalytic rate enhancement by the enzyme Ketosteroid Isomerase [247] and to uni-directional charge transfer in the photosynthetic reaction center [243]. Additionally we are pursuing a project to evaluate the accuracy of widely used molecular dynamics force fields in recapitulating experimentally observed spectra.

"Do Ligand Binding and Solvent Exclusion Alter the Electrostatic Character within the Oxyanion Hole of an Enzymatic Active Site", Paul Sigala, Aaron T. Fafarman, Patrick E. Bogard, Steven G. Boxer, and Daniel Herschlag, JACS, 129, 12104-12105 (2007). [pdf]

"Site-Specific Conversion of Cysteine Thiols into Thiocyanate Creates an IR Probe for Electric Fields in Proteins ", Aaron T. Fafarman, Lauren J. Webb, Jessica I. Chuang, and Steven G. Boxer, J. Am. Chem. Soc., 128, 13356-13357 (2006). [pdf] [Supplement]