CEST and DEST Experiments

Introduction

Many important biological processes, such as protein folding, misfolding, ligand binding, enzyme catalysis, and molecular recognition, are often better explained, not only by assuming the single highly populated conformation (major state) but also by assuming conformers populated at very low levels (minor states). Some of such minor states are not detected in traditional NMR spectra because of their low populations but are detectable through the exchange process with the major state by NMR. Compared to other spectroscopic techniques, such as circular dichroism and fluorescence spectroscopy that provide only population weighted-average signals, the detection of minor species through observation of a signal from the major species is a unique advantage of NMR. Recent developments in NMR methodology have provided extensive information about such “invisible” minor conformers that exchange with major species over a wide range of timescale. These experiment include measurement of...