Probing electric fields in proteins in solution by NMR spectroscopy.

Electric fields generated in native proteins affect almost every aspect of protein function. We present a method that probes changes in the electric field at specific locations within a protein. The method utilizes the dependence of the amide (1)H and (15)N NMR chemical shifts on electric charges in proteins. Charges were introduced at different positions in the blue copper protein plastocyanin, by protonation of side chains or by substitution of the metal ion. It is found that the associated chemical shift perturbations (CSPs) stem mainly from long-range electric field effects caused by the change in the electric charge. It is demonstrated that the CSPs can be used to estimate the dielectric constant at different locations in the protein, estimate the nuclear shielding polarizability, or position charges in proteins. 2008 Wiley-Liss, Inc.