Identification of an epitope on the recombinant bovine PrP that is able to elicit a prominent immune response in wild-type mice

Regional distribution of anchorless prion protein, PrP226*, in the human brain

It was shown previously that truncated molecules of prion protein can be found in brains of patients with some types of transmissible spongiform encephalopathy. One such molecule, PrP226*, is a fragment of prion protein, truncated at Tyr226. It was found to be present in aggregates, from which it can be released using chaotropic salts. In this study we investigated the distribution of PrP226* in Creutzfeldt–Jakob disease affected human brain, employing the mAb V5B2, specifically recognizing this fragment. The results show that PrP226* is not evenly distributed among different regions of human brain. Among brain regions analyzed, the fragment was found most likely to be accumulated in the cerebellum. Its distribution correlates with the distribution of PrP^Sc.

Establishment of bovine prion peptide-based monoclonal antibodies for identifying bovine prion

To obtain high titer monoclonal antibodies (McAbs) which can react with mammalian prion protein (PrP), Balb/C mice were immunized with bovine (Bo) PrP peptide (BoPrP 209-228 aa) coupled to keyhole limpet hemocyanin (KLH). The hybridoma cell lines secreting monoclonal antibodies against the peptide were established by cell fusion and cloning. The obtained McAbs were applied to detect recombinant human, bovine and hamster PrP, cellular prion protein (PrP(c)) in normal bovine brain and pathogenic scrapie prion protein (PrP(Sc)) accumulated in the medulla oblongata of bovine spongiform encephalopathy(BSE)specimen with Western blot and immunohistochemical detection, respectively. The current procedure might offer a simple, feasible method to raise high titer antibodies for studying biological features of PrP in mammals, as well as detection of transmissible spongiform encephalopathy (TSE) and diagnosis of BSE, in particular.

Anti-idiotypic antibodies: a new approach in prion research

Background

In certain cases, anti-idiotypic antibodies that recognize an antigen-combining site of an antibody can mimic the structure and/or function of certain nominal antigens. This feature makes them particularly useful if conventional experimental approaches fail to fulfil expectations, especially when the molecule of interest is infectious, toxic or difficult to isolate and purify. We suggest the application of an anti-idiotype concept to the field of prion biology, with the aim of evoking a humoral immune response against the pathological isoform of the prion protein (PrP^Sc). Different ways to induce anti-idiotypic responses were studied in mice and chickens using various forms of V5B2, a PrP^Sc-specific monoclonal antibody we have described previously.

Results

The preparation of anti-idiotypic monoclonal antibodies was achieved with well-defined strategies of immunization, selection and subsequent characterization. Our results demonstrate that it is possible to induce a strong anti-idiotypic immune response against the V5B2 monoclonal antibody in both xenogeneic and syngeneic experimental systems. From the competition seen between polyclonal and monoclonal anti-idiotypic antibodies and the original immunogen, the P1 peptide, and even more importantly, the ultimate target antigen, PrP^Sc, we conclude that selected antibodies bind to the antigen-combining site of the V5B2 monoclonal antibody and might even resemble the PrP^Sc-specific epitope. The involvement of both antigen-combining sites in the interaction between V5B2 and the most promising monoclonal anti-idiotypic antibody was further supported by molecular docking.

Conclusion

The results of the present study not only provide an example of the successful production of Ab2 monoclonal antibodies based on a well planned strategy for selection, but should also provide a new experimental approach that is applicable to the field of prion diseases.

The key-role of tyrosine 155 in the mechanism of prion transconformation as highlighted by a study of sheep mutant peptides

Prion protein is a strongly conserved and ubiquitous glycoprotein. The conformational conversion of the non-pathogenic cellular prion isoform (PrP(C)) into a pathogenic scrapie isoform (PrP(Sc)) is a fundamental event in the onset of transmissible spongiform encephalopathies (TSE). During this conversion, helix H1 and its two flanking loops are known to undergo a conformational transition into a beta-like structure. In order to understand mechanisms which trigger this transconformation, sheep prion protein synthetic peptides spanning helix 1 and beta-strand 2 (residues 142-166) were studied: (1) the N3 peptide, studied earlier, is known to fold into beta-hairpin-like conformation in phosphate buffer at neutral pH and to adopt a helix H1 conformation when dissolved in trifluoroethanol/phosphate buffer mixture, (2) The R156A mutant (peptide R15) and (3) the Y155A mutant (peptide Y14) of the N3 peptide are studied by circular dichroism and NMR spectroscopy in this article. Structural characterization of these peptides highlights the key role of tyrosine 155 in the stabilization of the beta-hairpin-like conformation of the sheep peptide in phosphate buffer. We propose a model where tyrosine 155 could stabilize the beta-hairpin structure by creating a hydrophobic core in phosphate buffer, necessary to initiate the beta-type structure formation. In the turn, the side chain ionic interaction, E152-R156 described before, seems to play a minor role relative to the hydrophobic packing, as observed with the R156A mutation (peptide R15). Interestingly, homology at amino acid residue 155 could be responsible for the species barrier in TSE.