Protein apparent dielectric constant and its temperature dependence from remote chemical shift effects.

A NMR protocol is introduced that permits accurate measurement of minute, remote chemical shift perturbations (CSPs), caused by a mutation-induced change in the electric field. Using protein GB3 as a model system, (1)H(N) CSPs in K19A and K19E mutants can be fitted to small changes in the electric field at distal sites in the protein using the Buckingham equation, yielding an apparent dielectric constant εa of 8.6 ± 0.8 at 298 K. These CSPs, and their derived εa value, scale strongly with temperature. For example, CSPs at 313 K are about ∼30% smaller than those at 278 K, corresponding to an effective εa value of about 7.3 at 278 K and 10.5 at 313 K. Molecular dynamics simulations in explicit solvent indicate that solvent water makes a significant contribution to εa.