Site-Specific Conversion of Cysteine Thiols into Thiocyanate Creates an IR Probe for Electric Fields in Proteins

J. Am. Chem. Soc., 128 (41), 13356 -13357, 2006. 10.1021/ja0650403 S0002-7863(06)05040-2
Web Release Date: September 27, 2006

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*

Department of Chemistry, Stanford University, Stanford, California 94305-5080

sboxer@stanford.edu

Received July 14, 2006

Abstract:

The nitrile stretching mode of the thiocyanate moiety is a nearly ideal probe for measuring the local electric field arising from the organized environment of the interior of a protein. Nitriles were introduced into three proteins: ribonuclease S (RNase S), human aldose reductase (hALR2), and the reaction center (RC) of Rhodobacter capsulatus, through a facile synthetic scheme for the transformation of cysteine residues into thiocyanatoalanine. Vibrational Stark effect spectroscopy and Fourier transform infrared spectroscopy on the modified proteins demonstrated that thiocyanate residues are a highly general tool for probing electrostatic fields in proteins.

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