Conformational stability of Syrian hamster prion protein PrP(90-231)

Abstract

Many transmissible spongiform encephalopathies (TSEs) are believed to be caused by a misfolded form of the normal cellular prion protein (PrP(C)) known as PrP(Sc). While PrP(Sc) is known to be exceptionally stable and resistant to protease degradation, PrP(C) has not shown these same unusual characteristics. However, using ion mobility spectrometry mass spectrometry (IMS-MS), we found evidence for at least one very stable conformation of a truncated form of recombinant PrP(C) consisting of residues 90-231, which resists unfolding in the absence of solvent at high injection energies and at temperatures in excess of 600 K. We also report the first absolute collision cross sections measured for recombinant Syrian hamster prion protein PrP(90-231).

Figure 1

Mass spectrum of α-PrP at pH 7.5. The numbers above the peaks correspond to z/n, where z is the charge and n is the oligomer order.

Figure 2

Representative ATDs for each charge state of α-PrP taken at an injection voltage of 50 V. The specific ATDs shown are (a) +13, (b) +10, and (c) +7. The labels are C = compact, I = intermediate, and E = extended.

Figure 3

Plot of cross section vs charge state for α-PrP data taken at pH 7.5. The measurements were reproducible to within 2%.

Figure 4

Injection energy dependence of α-PrP conformational stability. The +7 charge state (left) undergoes significant conversion to a more extended structure with increasing injection voltage, as do the +8 and +11 charge states (not shown). The +9 (right) and +10 (not shown) charge states retain their more compact structures up through 100 V.

Figure 5

Temperature dependence of α-PrP conformational stability. For every charge state with multiple conformations except +9 and +10, the protein isomerizes to its more extended structure between 425 and 475 K. The +10 charge state isomerizes to its more extended structure between 550 and 575 K, and remarkably, the +9 charge state resists conversion up through 600 K.