Abstract
Several solid-state NMR techniques have been introduced recently to measure nanometer distances involving (19)F, whose high gyromagnetic ratio makes it a potent nuclear spin for structural investigation. These solid-state NMR techniques either use (19)F correlation with (1)H or (13)C to obtain qualitative interatomic contacts or use the rotational-echo double-resonance (REDOR) pulse sequence to measure quantitative distances. However, no NMR technique is yet available for disambiguating (1)H-(19)F distances in multiply fluorinated proteins and protein-ligand complexes. Here, we introduce a three-dimensional (3D) (19)F-(15)N-(1)H correlation experiment that resolves the distances of multiple fluorines to their adjacent amide protons. We show that optimal polarization transfer between (1)H and (19)F spins is achieved using an out-and-back (1)H-(19)F REDOR sequence. We demonstrate this 3D correlation experiment on the model protein GB1 and apply it to the multidrug-resistance transporter, EmrE, complexed to a tetrafluorinated substrate. This technique should be useful for resolving and assigning distance constraints in multiply fluorinated proteins, leading to significant savings of time and precious samples compared to producing several singly fluorinated samples. Moreover, the method enables structural determination of protein-ligand complexes for ligands that contain multiple fluorines.