Dynamic Nuclear Polarization Magic Angle Spinning NMR Combined with MD Simulations Permits Detection of Order and Disorder in Viral Assemblies.

We report dynamic nuclear polarization (DNP)-enhanced magic-angle spinning (MAS) NMR spectroscopy in viral capsids from HIV-1 and bacteriophage AP205. Viruses regulate their life cycles and infectivity through modulation of their structures and dynamics. While static structures of capsids from several viruses are now accessible with near-atomic-level resolution, atomic-level understanding of functionally important motions in assembled capsids is lacking. We observed up to 64-fold signal enhancements by DNP, which permitted in-depth analysis of these assemblies. For the HIV-1 CA assemblies, a remarkably high spectral resolution in the 3D and 2D heteronuclear data sets permitted the assignment of a significant fraction of backbone and side-chain resonances. Using an integrated DNP MAS NMR and molecular dynamics (MD) simulation approach, the conformational space sampled by the assembled capsid at cryogenic temperatures was mapped. Qualitatively, a remarkable agreement was observed for the experimental C-13/N-15 chemical shift distributions and those calculated from substructures along the MD trajectory. Residues that are mobile at physiological temperatures are frozen out in multiple conformers at cryogenic conditions, resulting in broad experimental and calculated chemical shift distributions. Overall, our results suggest that DNP MAS NMR measurements in combination with MD simulations facilitate a thorough understanding of the dynamic signatures of viral capsids.