Nitrogen-detected TROSY yields comparable sensitivity to proton-detected TROSY for non-deuterated, large proteins under physiological salt conditions

Direct detection of the TROSY component of proton-attached ¹⁵N nuclei (¹⁵N-detected TROSY) yields high quality spectra with high field magnets, by taking advantage of the slow ¹⁵N transverse relaxation. The slow transverse relaxation and narrow line width of the ¹⁵N-detected TROSY resonances are expected to compensate for the inherently low ¹⁵N sensitivity. However, the sensitivity of ¹⁵N-detected TROSY in a previous report was one-order of magnitude lower than in the conventional ¹H-detected version. This could be due to the fact that the previous experiments were performed at low salt (0–50 mM), which is advantageous for ¹H-detected experiments. Here, we show that the sensitivity gap between ¹⁵N and ¹H becomes marginal for a non-deuterated, large protein (τ_c = 35 ns) at a physiological salt concentration (200 mM). This effect is due to the high salt tolerance of the ¹⁵N-detected TROSY. Together with the previously reported benefits of the ¹⁵N-detected TROSY, our results provide further support for the significance of this experiment for structural studies of macromolecules when using high field magnets near and above 1 GHz