Embedding a Reporter

Abstract

CHEMISTRY The nitrile (CN) group can be a useful infrared reporter in proteins because it has a strong stretching vibration near ∼2200 cm−1, a spectral region usually free from interfering absorptions in a biochemical environment. Schultz et al. have devised a protocol to introduce the non-naturally occurring amino acid para- cyano-l-phenylalanine (pCNPhe) into proteins during bacterial synthesis, using an orthogonal nonsense suppressor transfer RNA (tRNA) paired with an aminoacyl tRNA synthetase derived from Methanococcus janannaschi. They apply this system to incorporate the pCNPhe reporter in place of a histidine residue (His64) near the ligand-binding site of the heme group in myoglobin. When water was bound in the active site, they observed an 11-cm−1 shift in frequency relative to pCNPhe absorption in pure water or buffer solution, a change consistent with increased water polarity in the binding pocket. Changes in the observed CN stretching frequency were also consistent with the bent conformations of Fe(II)-bound NO and O2, as well as the linear CO-Fe(II) complex. — PDS J. Am. Chem. Soc. 128 , 10.1021/ja0636690 (2006).