15N-Detected TROSY NMR experiments to study large disordered proteins in high-field magnets.

Intrinsically disordered regions (IDRs) of proteins are critical in the regulation of biological processes but difficult to study structurally. Nuclear magnetic resonance (NMR) is uniquely equipped to provide structural information on IDRs at atomic resolution; however, existing NMR methods often pose a challenge for large molecular weight IDRs. Resonance assignment of IDRs using 15ND-detection was previously demonstrated and shown to overcome some of these limitations. Here, we improve the methodology by overcoming the need for deuterated buffers and provide better sensitivity and resolution at higher magnetic fields and physiological salt concentrations using transverse relaxation optimized spectroscopy (TROSY). Finally, large disordered regions with low sequence complexity can be assigned efficiently using these new methods as demonstrated by achieving near complete assignment of the 398-residue N-terminal IDR of the transcription factor NFAT1 harboring 18% prolines.