The measurement of small nuclear overhauser effects in the 1H spectra of proteins, and their application to lysozyme

Abstract

A simple differential technique for observing small Overhauser effects in 1H spectra detected in the Fourier transform mode is described, equivalent to the homonuclear INDOR experiment in the continuous-wave mode. When the ring-current-shifted apolar resonances in lysozyme were irradiated using this technique, selective negative Overhauser effects were produced in the rest of the spectrum. This enabled other proton resonances in the same amino acid residues to be assigned. It also caused aromatic and exchangeable NH resonances to appear in the difference spectra, arising from the proximity of the apolar groups to the aromatic rings which cause the ring current perturbations. It is shown how these effects aid assignment in a protein of known structure, and can in principle give structural information about a protein of unknown structure.