4D solid-state NMR for protein structure determination.

Solid-state NMR offers the chance to extend structural studies to proteins that are otherwise difficult to study at atomic resolution, such as protein fibrils, membrane proteins or poorly diffracting crystals. As two-dimensional spatial correlation NMR spectra of proteins suffer from severe resonance overlap, we analyze in this perspective article the potential of higher-dimensional (3D and 4D) proton-detected experiments, which have an increased number of identifiable and assignable distance restraints for solid-state structural studies. We discuss practical considerations for the NMR measurements and the preparation of suitable protein samples and show results of structure calculations from 4D solid-state NMR spectra.