Off-resonance 13C-2H REDOR NMR for site-resolved studies of molecular motion

Carbon-detected deuterium solid-state NMR rotating frame relaxation measurements for protein methyl groups under magic angle spinning

Deuterium rotating frame solid-state NMR relaxation measurements (2H R1ρ) are important tools in quantitative studies of molecular dynamics. We demonstrate how 2H to 13C cross-polarization (CP) approaches under 10-40 kHz magic angle spinning rates can be combined with the 2H R1ρ blocks to allow for extension of deuterium rotating frame relaxation studies to methyl groups in biomolecules. This extension permits detection on the 13C nuclei and, hence, for the achievement of site-specific resolution. The measurements are demonstrated using a nine-residue low complexity peptide with the sequence GGKGMGFGL, in which a single selective -13CD3 label is placed at the methionine residue. Carbon-detected measurements are compared with the deuterium direct-detection results, which allows for fine-tuning of experimental approaches. In particular, we show how the adiabatic respiration CP scheme and the double adiabatic sweep on the 2H and 13C channels can be combined with the 2H R1ρ relaxation rates measurement. Off-resonance 2H R1ρ measurements are investigated in addition to the on-resonance condition, as they extent the range of effective spin-locking field.

Three Decades of REDOR in Protein Science: A Solid-State NMR Technique for Distance Measurement and Spectral Editing

Solid-state NMR (ss-NMR) is a powerful tool to investigate noncrystallizable, poorly soluble molecular systems, such as membrane proteins, amyloids, and cell walls, in environments that closely resemble their physical sites of action. Rotational-echo double resonance (REDOR) is an ss-NMR methodology, which by reintroducing heteronuclear dipolar coupling under magic angle spinning conditions provides intramolecular and intermolecular distance restraints at the atomic level. In addition, REDOR can be exploited as a selection tool to filter spectra based on dipolar couplings. Used extensively as a spectroscopic ruler between isolated spins in site-specifically labeled systems and more recently as a building block in multidimensional ss-NMR pulse sequences allowing the simultaneous measurement of multiple distances, REDOR yields atomic-scale information on the structure and interaction of proteins. By extending REDOR to the determination of 1H-X dipolar couplings in recent years, the limit of measurable distances has reached ~15-20 Å, making it an attractive method of choice for the study of complex biomolecular assemblies. Following a methodological introduction including the most recent implementations, examples are discussed to illustrate the versatility of REDOR in the study of biological systems.

Deuteron off-resonance rotating frame relaxation for the characterization of slow motions in rotating and static solid-state proteins

We demonstrate the feasibility of deuterium solid-state NMR off-resonance rotating frame relaxation measurements for studies of slow motions in biomolecular solids. The pulse sequence, which includes adiabatic pulses for magnetization alignment, is illustrated for static and magic-angle spinning conditions away from rotary resonances. We apply the measurements for three systems with selective deuterium labels at methyl groups: a) a model compound, Fluorenylmethyloxycarbonyl methionine-D3 amino acid, for which the principles of the measurements and corresponding motional modeling based on rotameric interconversions are demonstrated; b) amyloid-β1-40 fibrils labeled at a single alanine methyl group located in the disordered N-terminal domain. This system has been extensively studied in prior work and here serves as a test of the method for complex biological systems. The essential features of the dynamics consist of large-scale rearrangements of the disordered N-terminal domain and the conformational exchange between the free and bound forms of the domain, the latter one due to transient interactions with the structured core of the fibrils. and c) a 15-residue helical peptide which belongs to the predicted α-helical domain near the N-terminus of apolipoprotein B. The peptide is solvated with triolein and incorporates a selectively labeled leucine methyl groups. The method permits model refinement, indicating rotameric interconversions with a distribution of rate constants.