Effective strategy to assign 1H-15N heteronuclear correlation NMR signals from lysine side-chain NH3+ groups of proteins at low temperature

Recent studies have shown that lysine side-chain NH3 (+) groups are excellent probes for NMR investigations of dynamics involving hydrogen bonds and ion pairs relevant to protein function. However, due to rapid hydrogen exchange, observation of H-1-N-15 NMR cross peaks from lysine NH3 (+) groups often requires use of a relatively low temperature, which renders difficulty in resonance assignment. Here we present an effective strategy to assign H-1 and N-15 resonances of NH3 (+) groups at low temperatures. This strategy involves two new H-1/C-13/N-15 triple-resonance experiments for lysine side chains. Application to a protein-DNA complex is demonstrated.