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Vibrational Stark Effect (VSE) in Proteins
Stark Spectroscopy
  About the Figure: Top: Scheme for post translational modification of cysteines. Bottom left: IR absorption (top, left axis) and VSE (red, bottom, right axis) spectra for 11 mM ribonuclease S with homocysteine introduced at position 13 and labeled with CN. The VSE spectrum is the field-on minus field-off difference spectrum obtained at 77 K in a 50/50 (v/v) glycerol/water glass. Bottom right: zoomed in view of ribonuclease structure with thiocyanate in stick representation, the helix it resides on in blue cartoon representation and the nearby residues in semi-transparent space-filing representation with carbon in grey, nitrogen in blue and oxygen in red.  

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.

  Recent Publications      

"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]

The Boxer LaboratoryStanford UniversityDepartment of Chemistry • 380 Roth Way, Stanford, California, 94305-5012 • (650) 723-4482
Questions about this website may be directed to Debra Frank. • Website updated March 2012.