Site-specific conversion of cysteine thiols into thiocyanate creates an IR probe for electric fields in proteins.
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.
Fafarman
Aaron T
AT
Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA.
Webb
Lauren J
LJ
Chuang
Jessica I
JI
Boxer
Steven G
SG
D003545:Cysteine / Q000737:chemistry*; D004574:Electromagnetic Fields; D015202:Protein Engineering / Q000379:methods*; D011506:Proteins / Q000032:analysis* / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods*; D055672:Static Electricity; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013696:Temperature; D013861:Thiocyanates / Q000138:chemical synthesis*
D011506:Proteins; D013438:Sulfhydryl Compounds; D013861:Thiocyanates; D003545:Cysteine; C031760:thiocyanate