Dynamics of a truncated prion protein, PrP(113–231), from 15N NMR relaxation: Order parameters calculated and slow conformational fluctuations localized to a distinct region
Open Access
- 29 December 2008
- journal article
- research article
- Published by Wiley in Protein Science
- Vol. 18 (2), 410-423
- https://doi.org/10.1002/pro.44
Abstract
Prion diseases are associated with the misfolding of the prion protein (PrPC) from a largely α‐helical isoform to a β‐sheet rich oligomer (PrPSc). Flexibility of the polypeptide could contribute to the ability of PrPC to undergo the conformational rearrangement during PrPC–PrPSc interactions, which then leads to the misfolded isoform. We have therefore examined the molecular motions of mouse PrPC, residues 113–231, in solution, using 15N NMR relaxation measurements. A truncated fragment has been used to eliminate the effect of the 90‐residue unstructured tail of PrPC so the dynamics of the structured domain can be studied in isolation. 15N longitudinal (T1) and transverse relaxation (T2) times as well as the proton‐nitrogen nuclear Overhauser effects have been used to calculate the spectral density at three frequencies, 0, ωN, and 0.87ωH. Spectral densities at each residue indicate various time‐scale motions of the main‐chain. Even within the structured domain of PrPC, a diverse range of motions are observed. We find that removal of the tail increases T2 relaxation times significantly indicating that the tail is responsible for shortening of T2 times in full‐length PrPC. The truncated fragment of PrP has facilitated the determination of meaningful order parameters (S2) from the relaxation data and shows for the first time that all three helices in PrPC have similar rigidity. Slow conformational fluctuations of mouse PrPC are localized to a distinct region that involves residues 171 and 172. Interestingly, residues 170–175 have been identified as a segment within PrP that will form a steric zipper, believed to be the fundamental amyloid unit. The flexibility within these residues could facilitate the PrPC–PrPSc recognition process during fibril elongation.Keywords
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