Prion Proteins with Pathogenic and Protective Mutations Show Similar Structure and Dynamics

摘要

Conformational change in the prion protein (PrP) is thought to be responsible for a group of rarenbut fatal neurodegenerative diseases of humans and other animals, including Creutzfeldt-Jakob disease andnbovine spongiform encephalopathy. However, little is known about the mechanism by which normal cellularnPrPs initiate and propagate the conformational change. Here, we studied backbone dynamics of the inheritednpathogenic mutants (P101L and H186R), protective mutants (Q167R and Q218K), and wild-type mousenPrP(89-230) at pH 5.5 and 3.5. Mutations result in minor chemical shift changes around the mutationnsites except that H186R induces large chemical shift changes at distal regions. At lower pH values, thenC-terminal half of the second helix is significantly disordered for the wild-type and all mutant proteins, whilenother parts of the protein are essentially unaffected. This destabilization is accompanied by protonation of thenpartially exposed histidine H186 in the second helix of the wild-type protein. This region in the mutant proteinnH186R is disordered even at pH 5.5. The wild-type and mutant proteins have similar microsecondnconformational exchange near the two β-strands and have similar nanosecond internal motions in severalnregions including the C-terminal half of the second helix, but only wild type and P101L have extensivennanosecond internal motions throughout the helices. These motions mostly disappear at lower pH. Ournfindings raise the possibility that the pathogenic or dominant negative mutations exert their effects on somennon-native intermediate form such as PrP* after conversion of cellular PrP (PrPC) into the pathogenic isoformnPrPSc has been initiated; additionally, formation of PrPSc might begin within the C-terminal folded regionnrather than in the disordered N-terminal region.