Nutation frequency modulation on NMR signal of nuclear spins in chemical exchange with solvent water under the BEST conditions

Solvent exchange properties of protein backbone amide protons provide valuable residue‐specific information on protein solvent accessibility, structure stability and flexibility and hence are of significant interest in structural biology. NMR has served as a unique means for the characterization of chemical exchange including proton amide exchange with solvent water at residue‐specific levels across a broad range of exchange rates. One of the methods used for the characterization of protein backbone amide exchange by NMR involves the use of progressive selective irradiation of the water resonance. Here, we report the experimental observation of the nutation frequency (strength of RF field used for the irradiation of water resonance) modulation on amide proton signals for those in exchange with the solvent water under the band‐selective excitation short transient (BEST) conditions. Compared with conventional saturation transfer of water magnetization experiments, this nutation frequency modulation observed on signal of nuclear spins under the BEST conditions potentially offers a quick identification of protein backbone amides in rapid exchange with solvent water. Copyright © 2014 John Wiley & Sons, Ltd.