Two-Field Transverse Relaxation-Optimized Spectroscopy for the Study of Large Biomolecules – an in Silico Investigation

Biomolecular NMR spectroscopy has greatly benefited from the development of TROSY-type pulse sequences, in pair with specific labeling. The selection of spin operators with favorable relaxation properties has led to an increase in the resolution and sensitivity of spectra of large biomolecules. However, nuclei with a large chemical shift anisotropy (CSA) contribution to relaxation can still suffer from large linewidths at conventional magnetic fields (higher than 9 T). Here, we introduce the concept of two-field TROSY (2F-TROSY) where the chemical shifts of nuclei with large CSA is labeled at low fields (ca. 2 T) dramatically reducing the contribution of CSA to relaxation. Signal detection is performed at high field (> 9 T) on a nucleus with efficient TROSY interference to yield high-resolution and sensitivity. We use comprehensive numerical simulations to demonstrate the power of this approach on aromatic 13C-19F spin pairs for which a TROSY pulse sequence has recently been published. We predict that the 2F- TROSY experiment shall yield good quality spectra for large proteins (global tumbling correlation times as high as 100 ns) with one order of magnitude higher sensitivity than the single-field experiment.