Rapid measurement of long-range distances in proteins by multidimensional 13C–19F REDOR NMR under fast magic-angle spinning

Abstract

The ability to simultaneously measure many long-range distances is critical to efficient and accurate determination of protein structures by solid-state NMR (SSNMR). So far, the most common distance constraints for proteins are [subscript 13]C-[subscript 15]N distances, which are usually measured using the rotational-echo double-resonance (REDOR) technique. However, these measurements are restricted to distances of up to ~ 5 Å due to the low gyromagnetic ratios of [subscript 15]N and [subscript 13]C. Here we present a robust 2D [subscript 13]C–[subscript 19]F REDOR experiment to measure multiple distances to ~ 10 Å. The technique targets proteins that contain a small number of recombinantly or synthetically incorporated fluorines. The [subscript 13]C–19F REDOR sequence is combined with 2D [subscript 13]C–[subscript 13]C correlation to resolve multiple distances in highly [subscript 13]C-labeled proteins. We show that, at the high magnetic fields which are important for obtaining well resolved [subscript 13]C spectra, the deleterious effect of the large [subscript 19]F chemical shift anisotropy for REDOR is ameliorated by fast magic-angle spinning and is further taken into account in numerical simulations. We demonstrate this 2D [subscript 13]C–[subscript 13]C resolved [subscript 13]C–[subscript 19]F REDOR technique on [subscript 13]C, [subscript 15]N-labeled GB1. A 5[superscript -19]F-Trp tagged GB1 sample shows the extraction of distances to a single fluorine atom, while a [subscript 3-19]F-Tyr labeled GB1 sample allows us to evaluate the effects of multi-spin coupling and statistical [subscript 19]F labeling on distance measurement. Finally, we apply this 2D REDOR experiment to membrane-bound influenza BM2 transmembrane peptide, and show that the distance between the proton-selective histidine residue and the gating tryptophan residue differs from the distances in the solution NMR structure of detergent-bound BM2. This 2D [subscript 13]C–[subscript 19]F REDOR technique should facilitate SSNMR-based protein structure determination by increasing the measurable distances to the ~ 10 Å range.