Determination of Peptide Backbone Torsion Angles Using Double-Quantum Dipolar Recoupling Solid-State NMR Spectroscopy

Abstract

Several approaches for utilizing dipolar recoupling solid-state NMR (ssNMR) techniques to determine local structure at high resolution in peptides and proteins have been developed. However, many of these techniques measure only one torsion angle or are accurate for only certain classes of secondary structure. Additionally, the efficiency with which these dipolar recoupling experiments suppress the deleterious effects of chemical shift anisotropy (CSA) at high magnetic field strengths varies. Dipolar recoupling with a windowless sequence (DRAWS) has proven to be an effective pulse sequence for exciting double-quantum (DQ) coherences between adjacent carbonyl carbons along the peptide backbone. By allowing this DQ coherence to evolve, it is possible to measure the relative orientations of the CSA tensors and subsequently use this information to determine the Ramachandran torsion angles phi and psi. Here, we explore the accuracies of the assumptions made in interpreting DQ-DRAWS data and demonstrate their fidelity in measuring torsion angles corresponding to a variety of secondary structures irrespective of hydrogen-bonding patterns. It is shown how a simple choice of isotopic labels and experimental conditions allows accurate measurement of backbone secondary structures without any prior knowledge. This approach is considerably more sensitive for determining structure in helices and has comparable accuracy for beta-sheet and extended conformations relative to other methods. We also illustrate the ability of DQ-DRAWS to distinguish between structures in heterogeneous samples.

Proton micro-magic-angle-spinning NMR spectroscopy of nanoliter samples

“…7b for the different 13 C sites. We confirmed our assignment by density functional theory (DFT) calculations using QUANTUM ESPRESSO [42] explicitly taking the periodicity in the crystal structure of AGG [43] into account. Our assignment of the 13 C resonances is in agreement with the one of Luca et al [44] and corrects the one presented recently in Ref.…”

The Helical Structure of Surfactant Peptide KL4 When Bound to POPC: POPG Lipid Vesicles

“…Thus, double-quantum buildup experiments were used to measure the distances between adjacent 13 C’ positions in KL 4 , stemming from the 1/r 3 dependence of the dipolar coupling. Previously we have demonstrated this technique can successfully measure internuclear distances in order to determine the torsion angle Φ over a range of secondary structures with an rmsd of 0.03 Å for distance or 4° for Φ relative to X-ray structures (49). The dipolar recoupling data collected on all four pairs of 13 C’ labels are shown in Figure 3 along with simulations that best fit the data.…”

A low-E magic angle spinning probe for biological solid state NMR at 750MHz

“…These experiments are useful at intermediate rotation rates (5-8 kHz) for determining torsion angles in peptides [27], yet, like many recoupling sequences, their performance is dependent on the availability of strong, homogeneous B 1 fields [28]. For these experiments, the CP contact time was 2.2 ms, cw decoupling was applied during the mixing period and SPINAL64 decoupling [16] was applied during acquisition.…”