A unique and simple approach to improve sensitivity in 15N-NMR relaxation measurements for NH3+ groups: Application to a protein-DNA complex

NMR spectroscopy is a powerful tool for research on protein dynamics. In the past decade, there has been significant progress in the development of NMR methods for studying charged side chains. In particular, NMR methods for lysine side-chain NH3+ groups have been proven to be powerful for investigating the dynamics of hydrogen bonds or ion pairs that play important roles in biological processes. However, relatively low sensitivity has been a major practical issue in NMR experiments on NH3+ groups. In this paper, we present a unique and simple approach to improve sensitivity in 15N relaxation measurements for NH3+ groups. In this approach, the efficiency of coherence transfers for the desired components are maximized, whereas undesired anti-phase or multi-spin order components are purged through pulse schemes and rapid relaxation. For lysine side-chain NH3+ groups of a protein-DNA complex, we compared the data obtained with the previous and new pulse sequences under the same conditions and confirmed that the 15N relaxation parameters were consistent for these datasets. While retaining accuracy in measuring 15N relaxation, our new pulse sequences for NH3+ groups allowed an 82% increase in detection sensitivity of 15N longitudinal and transverse relaxation measurements.