Quantitation of rapid proton-deuteron amide exchange using hadamard spectroscopy

The rates of amide proton exchange in protein backbones are very useful reporters of accessibility and structural stability of specific residues and secondary structure elements. Measurement by monitoring changes in intensity of cross-peaks in standard N-15-H-1 HSQC spectra as protons are replaced by solvent deuterons has become widely accepted. However, these methods are limited to relatively slow rates due to time limitations of the conventional 2D HSQC experiment. Here we show that a Hadamard encoded version of the HSQC, which relies on a multiplexed, frequency selective, excitation in the N-15 dimension, extends application to rates that are as much as an order of magnitude faster than those previously accessible.