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Conformational Dynamics in the Core of Human Y145Stop Prion Protein Amyloid Probed by Relaxation Dispersion NMR.

ABSTRACT: Microsecond to millisecond timescale backbone dynamics of the amyloid core residues in Y145Stop human prion protein (PrP) fibrils were investigated by using 15 N rotating frame (R1? ) relaxation dispersion solid-state nuclear magnetic resonance spectroscopy over a wide range of spin-lock fields. Numerical simulations enabled the experimental relaxation dispersion profiles for most of the fibril core residues to be modelled by using a two-state exchange process with a common exchange rate of 1000?s-1 , corresponding to protein backbone motion on the timescale of 1?ms, and an excited-state population of 2?%. We also found that the relaxation dispersion profiles for several amino acids positioned near the edges of the most structured regions of the amyloid core were better modelled by assuming somewhat higher excited-state populations (?5-15?%) and faster exchange rate constants, corresponding to protein backbone motions on the timescale of ?100-300??s. The slow backbone dynamics of the core residues were evaluated in the context of the structural model of human Y145Stop PrP amyloid.

SUBMITTER: Shannon MD

PROVIDER: S-EPMC6342661 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Project description:Amyloid aggregates of a C-truncated Y145Stop mutant of human prion protein, huPrP23-144, associated with a heritable amyloid angiopathy, have previously been shown to contain a compact, relatively rigid, and beta-sheet-rich approximately 30-residue amyloid core near the C-terminus under physiologically relevant conditions. In contrast, the remaining huPrP23-144 residues display considerable conformational dynamics, as evidenced by the absence of corresponding signals in cross-polarization (CP)-based solid-state NMR (SSNMR) spectra under ambient conditions and their emergence in analogous spectra recorded at low temperature on frozen fibril samples. Here, we present the direct observation of residues comprising the flexible N-terminal domain of huPrP23-144 amyloid by using 2D J-coupling-based magic-angle spinning (MAS) SSNMR techniques. Chemical shifts for these residues indicate that the N-terminal domain is effectively an ensemble of protein chains with random-coil-like conformations. Interestingly, a detailed analysis of signal intensities in CP-based 3D SSNMR spectra suggests that non-negligible molecular motions may also be occurring on the NMR time scale within the relatively rigid core of huPrP23-144 amyloid. To further investigate this hypothesis, quantitative measurements of backbone dipolar order parameters and transverse spin relaxation rates were performed for the core residues. The observed order parameters indicate that, on the submicrosecond time scale, these residues are effectively rigid and experience only highly restricted and relatively uniform motions similar to those characteristic for well-structured regions of microcrystalline proteins. On the other hand, significant variations in magnitude of transverse spin relaxation rates were noted for residues present at different locations within the core region and correlated with observed differences in spectral intensities. While interpreted only qualitatively at the present time, the extent of the observed variations in transverse relaxation rates is consistent with the presence of relatively slow, microsecond-millisecond time scale chemical exchange type phenomena within the huPrP23-144 amyloid core.

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Conformational Dynamics in the Core of Human Y145Stop Prion Protein Amyloid Probed by Relaxation Dispersion NMR.

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