Integrating F Distance Restraints for Accurate Protein Structure Determination by Magic Angle Spinning NMR Spectroscopy.

Traditional protein structure determination by magic angle spinning (MAS) solid-state NMR spectroscopy primarily relies on interatomic distances up to 8 Å, extracted from C-, N-, and H-based dipolar-based correlation experiments. Here, we show that F fast (60 kHz) MAS NMR spectroscopy can supply additional, longer distances. Using 4F-Trp,U-C,N crystalline agglutinin (OAA), we demonstrate that judiciously designed 2D and 3D F-based dipolar correlation experiments such as (H)CF, (H)CHF, and FF can yield interatomic distances in the 8-16 Å range. Incorporation of fluorine-based restraints into structure calculation improved the precision of Trp side chain conformations as well as regions in the protein around the fluorine containing residues, with notable improvements observed for residues in proximity to the Trp pairs (W10/W17 and W77/W84) in the carbohydrate-binding loops, which lacked sufficient long-range C-C distance restraints. Our work highlights the use of fluorine and F fast MAS NMR spectroscopy as a powerful structural biology tool.