Effective strategy to assign ¹H- ¹⁵N heteronuclear correlation NMR signals from lysine side-chain NH3₃⁺ 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 (1)H-(15)N 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 (1)H and (15)N resonances of NH3(+) groups at low temperatures. This strategy involves two new (1)H/(13)C/(15)N triple-resonance experiments for lysine side chains. Application to a protein-DNA complex is demonstrated.