Relative and Regional Stabilities of the Hamster, Mouse, Rabbit, and Bovine Prion Proteins toward Urea Unfolding Assessed by Nuclear Magnetic Resonance and Circular Dichroism Spectroscopies

The residue-specific urea-induced unfolding patterns of recombinant prion proteins from different species (bovine, rabbit, mouse, and Syrian hamster) were monitored using high-resolution 1H nuclear magnetic resonance (NMR) spectroscopy. Protein constructs of different lengths, and with and without a His tag attached at the N-terminus, were studied. The various species showed different overall sensitivities toward urea denaturation with stabilities in the following order: hamster ≤ mouse < rabbit < bovine protein. This order is in agreement with recent circular dichroism (CD) spectroscopic measurements for several species [Khan, M. Q. (2010) Proc. Natl. Acad. Sci. U.S.A. 107, 19808–19813] and for the bovine protein presented herein. The [urea]1/2 values determined by CD spectroscopy parallel those of the most stable residues observed by NMR spectroscopy. Neither the longer constructs containing an additional hydrophobic region nor the His tag influenced the stability of the structured domain of the constructs studied. The effect of the S174N mutation in rabbit PrPC was also investigated. The rank order of the regional stabilities within each protein remained the same for all species. In particular, the residues in the β-sheet region in all four species were more sensitive to urea-induced unfolding than residues in the α2 and α3 helical regions. These observations indicate that the regional specific unfolding pattern is the same for the four mammalian prion proteins studied but militate against the idea that PrPSc formation is linked with the global stability of PrPC.