Abstract
In structural studies of immobilized, aggregated and self-assembled biomolecules, solid-state NMR (ssNMR) spectroscopy can provide valuable high-resolution structural information. Among the structural restraints provided by magic angle spinning (MAS) ssNMR the canonical focus is on inter-atomic distance measurements. In the current review, we examine the utility of ssNMR measurements of angular constraints, as a complement to distance-based structure determination. The focus is on direct measurements of angular restraints via the judicious recoupling of multiple anisotropic ssNMR parameters, such as dipolar couplings and chemical shift anisotropies. Recent applications are highlighted, with a focus on studies of nanocrystalline polypeptides, aggregated peptides and proteins, receptor-substrate interactions, and small molecule interactions with amyloid protein fibrils. The review also examines considerations of when and where ssNMR torsion angle experiments are (most) effective, and discusses challenges and opportunities for future applications.
Highlights
In modern integrative structural biology, complementary structure determination methods provide insights into different aspects of the structure, dynamics and co-assembly of biomolecules
Whilst the orientation dependence of a single 15N-13C REDOR recoupling experiment is masked in a typical magic angle spinning (MAS) solid-state NMR (ssNMR) study, these two 15N-13C recoupling curves display an interference effect that results in behavior that is sensitive to the N-Cα-C′-N dihedral angle (Figure 2B)
The NCCN experiment minima are close to both the X-ray structure angles and the results of NCCN-based chemical shift analysis. This is illustrated in the bar graphs of Figure 2F. These results show that the NCCN experiment gives results that match the structure as known from X-ray microcrystallography (Nelson et al, 2005; van der Wel et al, 2007, 2010), consistent with earlier studies (Ladizhansky et al, 2003)
Summary
In modern integrative structural biology, complementary structure determination methods provide insights into different aspects of the structure, dynamics and co-assembly of biomolecules. Whilst the orientation dependence of a single 15N-13C REDOR recoupling experiment is masked in a typical MAS ssNMR study, these two 15N-13C recoupling curves display an interference effect that results in behavior that is sensitive to the N-Cα-C′-N dihedral angle (Figure 2B). By combining NCCN measurements and TALOS-based chemical shift analysis, it was shown that these two conformers reflect two types of β-strand structures with distinct backbone conformations (Figures 3A–D) (Hoop et al, 2016).
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