Ultrahigh-resolution solid-state NMR for high-molecular weight proteins on GHz-class spectrometers

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique with broad impact across the physical and life sciences, and ultrahigh field (UHF), gigahertz-class NMR spectrometers offer exceptional performance, including superior resolution and sensitivity. In solid-state NMR (SSNMR), resolution is primarily constrained by instrumentation rather than molecular tumbling, making it well suited for studying large and complex systems. To fully leverage UHF magnets for SSNMR, it is essential to eliminate line broadening arising from magnetic field drift and couplings among the nuclear spins. We address these challenges using external ²H lock to compensate for the field drift and long-observation-window band-selective homonuclear decoupling to suppress ¹³C homonuclear couplings. We achieve better than 0.2-parts per million resolution in proteins up to 144 kilodalton, enabling unique site resolution for more than 500 amide backbone pairs in two-dimensional experiments. This exceeds the resolution available from solution NMR for large biological molecules, greatly expanding the potential of gigahertz-class NMR for research in life sciences.