Mass spectrometry assisted assignment of NMR resonances in 15N labeled proteins.

Application of nuclear magnetic resonance (NMR) methods for the structural characterization to larger and more complex protein systems can be facilitated through the development of new methods for resonance assignment. Here, a novel approach that relies on integration of NMR and mass spectrometry (MS) methods is explored. The approach relies on the fact that both NMR and MS are able to monitor rates of exchange of amide protons for water deuterons. Correlating the rates can connect cross-peak positions from NMR data with fragment masses from MS data to support sequential assignment. The example provided is for a small model protein, ubiquitin, but the potential for application to large, more difficult to express proteins is clear.