Solid-state NMR mobility studies of cellular prion protein and amyloid-β oligomers

There is increasing awareness that the phase state of proteins has important implications for biochemical function, whether in stress granules, membrane-less organelles or as components of hydrogels. As semi-solids or highly viscous liquids, such phase states pose new challenges for characterization, and for correlating structure with function. One such system is the hydrogel phase¹ that forms when amyloid-β (Aβ) oligomers bind to cellular prion protein (PrP^c)², and has been recently implicated in the molecular mechanism of the onset of Alzheimer`s Disease. Understanding the dynamics of the protein components has proven important for developing a structural and dynamic model for this phase. Two types of NMR methods have proven especially informative. Backbone mobility has been probed by comparison of the temperature dependence of the thermally polarized ¹³C magic angle spinning NMR signal to the cross polarization (CP) enhanced signal. Since the CP enhancement of the carbonyl carbon arises from non-bonded ¹³C-¹H dipolar couplings, this proves to be a sensitive reporter of the range of backbone fluctuations¹. This method allowed us to observe the backbone motion in different constructs of the hydrogel to understand segmental mobility of PrP. Direct detection ¹⁵N NMR with observation of transient nuclear Overhauser effects (NOE) is also very informative. This differentiates sidechain ¹⁵N signals for highly mobile and rigid residues based on the sign of the NOE. The combination of these methods gives us a clearer picture of how PrP is behaving in the hydrogel as well as how it is interacting with Aβo.

1. Kostylev, M., et. al. Molecular Cell. 2018, 72, 426-443.

2. Lauren, J., et. al. Nature. 2009, 457, 1128-1132.