| Summary: | Mammalian prion protein is able to cause a multitude of neurological maladies, most notably the transmissible spongiform echephalopathies. All are characterised by the misfolding of a non-pathogenic form the cellular protein Prpc to a misfolded aggregated isoform Prpscwhich leads to neurotoxicity and apoptosis characterised by brain spongiosis and amyloid plaque deposits. The exact molecular mechanisms of pathogenicity remain unknown for both the transmissible and inherited forms of disease. An artificially generated deletion of residues 105-125 of Prpc, encoding largely hydrophobic amino acids, in the intrinsically disordered N-terminus of the protein is hig~ly neurotoxic and has been shown to mediate a TSE like phenotype when expressed in transgenic mice. A possible mechanism of action consistent with prion protein exhibiting varying isoforms is that the deletion mutant may fold to a structure comparative to that of a naturally occurring pathogenic form. Biochemical and biophysical characterisation of the deleted form of Prpc could support this possibility. To explore the role of residues 95-135 in protein folding an extended set of deletion mutants of the hydrophobic region were created and the encoded Prpc like proteins expressed and purified. Among the mutants made it was found that deletion of solely residues 105-125 within the hydrophobic region gave rise to subtle structural alterations when compared to parental Prpc. As Prpc is a GPI anchored protein normally associated with a membrane environment, membrane interaction assays were also performed with deletion mutants revealing that that a charge cluster and hydrophobic region acted synergistically to bind, insert into and disrupt anionic membranes. These findings did not support a mechanism of action for the deletion ~105-125 mediating toxicity through membrane pore formation but rather a subtle structural change that may be consistent with a receptor 4 mediated toxicity model. Possible further cellular and structural studies with defined deletions of Prpc with a view to deciphering the neurotoxic mode of action are discussed. 5
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