Influence of amino acid substitutions related to inherited human prion diseases on the thermodynamic stability of the cellular prion protein

Transmissible spongiform encephalopathies (TSEs) are caused by a unique inf ectious agent which appears to be identical with PrPSc, an oligomeric, misf olded isoform of the cellular prion protein, PrPC. All inherited forms of h uman TSEs, i.e., familial Creutzfeldt-Jakob disease, Gerstmann-Straussler-S cheinker syndrome, and fatal familial insomnia, segregate with specific poi nt mutations or insertions in the gene coding for human PrP. Here we have t ested the hypothesis that these mutations destabilize PrPC and thus facilit ate its conversion into PrPSc. Eight of the disease-specific amino acid rep lacements are located in the C-terminal domain of PrPC, PrP(121-231), which constitutes the only part of PrPC with a defined tertiary structure. Intro duction of all these replacements into PrP(121-231) yielded variants with t he same spectroscopic characteristics as wild-type PrP(121-231) and similar to full-length PrP(23-231), which excludes the possibility that the exchan ges a priori induce a PrPSc-like conformation. The thermodynamic stabilitie s of the variants do not correlate with specific disease phenotypes. Five o f the amino acid replacements destabilize PrP(121-231), but the other varia nts have the same stability as the wild-type protein. These data suggest th at destabilization of PrPC is neither a general mechanism underlying the fo rmation of PrPSc nor the basis of disease phenotypes in inherited human TSE s.