Prion protein conversions

Caughey, B. Prion protein conversions insight into mechanisms, TSE transmission barriers and strains. Br. Med. Bull. 66 109-120,2003. 

Prion Protein Conversion and the Biophysical Properties of PrPSc. 145... 

Fig. 5 Models of prion replication, (a) The template assistance model predicts that a PrPSo monomer is more stable than PrPc, but is kinetically inaccessible. In the rare event that a PrPSo monomer is created spontaneously (or provided exogenously), it can template the misfolding of another PrPc molecule by direct interaction. The dashed line shows that the newly created PrPSc monomer can act as another seed to formation of PrPSc. (b) The nucleation polymerization model predicts that barrier to prion protein conversion is the formation of a nucleus in which the protein adopts a PrPSo-like structure. The formation of such a low order aggregate is not favored however, once it has formed, polymerization from a pool of PrPc molecules can take place efficiently. Fragmentation of the polymer increases the number of ends for the recruitment of PrPc monomers...

There has been great interest in recent years in understanding the biophysical and structural aspects of prion protein conversion using bacterially-expressed rPrP. Depending on experimental conditions, rPrP has been shown to form a variety of oligomeric structures [75, 76, 127-131], However, of particular interest in the... 

Herrmann LM, Caughey B (1998) The importance of the disulfide bond in prion protein conversion. Neuroreport 9 2457... 

Supattapone S (2004) Prion protein conversion in vitro. J Mol Med 82 348-356 Tanimukai S, Hasegawa H, Nakai M, Yagi K, Hirai M, Saito N, Taniguchi T, Terashima A, Yasuda M, Kawamata T, Tanaka C (2002) Nanomolar amyloid beta protein activates a specific PKC isoform mediating phosphorylation of MARCKS in Neuio2A cells. Neuroreport 13 549-553... 

Kocisko DA, Priola SA, Raymond GJ, Chesebro B, Lansbury PT Jr, Caughey B. Species specificity in the cell-free conversion of prion protein to protease-resistant forms a model for the scrapie species barrier. Proc Natl Acad USA 1995 92 3923-3927. 

Saborio GP, Soto C, Kascsak RJ, Levy E, Kascsak R, Harris DA, Frangione B. Cell-lysate conversion of prion protein into its protease-resistant isoform suggests the participation of a cellular chaperone. Biochem Biophys Res Commun 1999 258 470-475. 

Jackson, G. S. et al. Reversible conversion of monomeric human prion protein between native and fibrilogenic conformations. Science 283 1935-1937,1999. 

Baskakov, I. V., and Bocharova, O. V. (2005). In vitro conversion of mammalian prion protein into amyloid fibrils displays unusual features. Biochemistry 44, 2339-2348. 

DeMarco, M. L., and Daggett, V. (2004). From conversion to aggregation Protofibril formation of the prion protein. Proc. Natl. Acad. Sci. USA 101, 2293-2298. Diaz-Avalos, R., Long, C., Fontano, E., Balbirnie, M., Grothe, R., Eisenberg, D., and Caspar, D. L. D. (2003). Cross-beta structure of an amyloid-forming peptide studied by electron nano-crystallography. Fibre Diffract. Rev. 11, 79-86. 

Pan, K. M., Baldwin, M., Nguyen, J., Gasset, M., Serban, A., Groth, D., Mehlhorn, I., Huang, Z., Fletterick, R. J., Cohen, F. E., and Prusiner, S. B. (1993). Conversion of alpha-helices into beta-sheets features in the formation of the scrapie prion proteins. Proc. Natl. Acad. Sci. USA 90, 10962-10966. 

Several NMR studies were carried out to gain insight into the molecular basis for the conversion of the PrP " into the pathogenic conformer, PrP . They mainly involve the study of prion-derived peptides believed to be essential for prion propagation, although other studies also include the investigation of the whole prion protein ° and prion mutants. 

Recently, high-pressure NMR measurements have enabled us to identify an intermediate conformer of the hamster prion protein, which has been suggested to be the PrP factor responsible for the PrP /PrP ° conversion or a closely related precursor. ... 

In inherited forms of prion diseases, a mutation in the gene encoding PrP produces a change in one amino acid residue that is believed to make the conversion of PrPG to PrPSc more likely. A complete understanding of prion diseases awaits new information about how prion protein affects brain function. Structural information about PrP is beginning to provide insights into the molecular process that allows the prion proteins to interact so as to alter their conformation (Fig. 2). 

A hard-to-understand aspect of the "protein-only" theory of prion diseases is the existence of various "strains" of prion proteins. These do not involve differences in amino acid sequence but differences in the conformations of the PrPSc forms and in the glycosylation patterns. dmw How can there be several different conformations of the same protein, all of which seed the conversion of normal PrP into differing insoluble forms In spite of this puzzle, support for the explanation of strain differences comes from a yeast prion system, which involves transcription termination factor eRF3.x z In this system, which involves a prion whose insoluble form can be redissolved by guanidine hydrochloride,aa differing strains have also been described.ybb cc Nevertheless, the presence of the various strains of animal prions, as well as observed vaccination of inbred mice against specific strains,dd may be more readily understood if the disease is transmitted by an unidentified virus rather than by a pure protein.1/U ee/ff In fact, the diseases have not been successfully transmitted by truly virus-free proteins synthesized from recombinant DNA.ee... 

What is the nature of the insoluble forms of the prion protein They are hard to study because of the extreme insolubility, but the conversion of a helix to (3 sheet seems to be fundamental to the process and has been confirmed for the yeast prion by X-ray diffraction.11 It has been known since the 1950s that many soluble a-helix-rich proteins can be transformed easily into a fibrillar form in which the polypeptide chains are thought to form a P sheet. The chains are probably folded into hairpin loops that form an antiparallel P sheet (see Fig. 2-ll).ii-11 For example, by heating at pH 2 insulin can be converted to fibrils, whose polarized infrared spectrum (Fig. 23-3A) indicates a cross-P structure with strands lying perpendicular to the fibril axis >mm Many other proteins are also able to undergo similar transformation. Most biophysical evidence is consistent with the cross-P structure for the fibrils, which typically have diameters of 7-12 rnn."-11 These may be formed by association of thinner 2 to 5 nm fibrils.00 However, P-helical structures have been proposed for some amyloid fibrils 3 and polyproline II helices for others. 1 11... 

Other IRRAS applications to peptides and proteins. In addition to the pulmonary surfactant system, a variety of other applications employing IRRAS to study peptide and protein conformation and orientation have appeared. The secondary structure conversion of the amyloid (prion)-protein in the normal form into the abnormal form is the main cause of several human and animal diseases, such as Alzheimer s disease [68]. The secondary structure of the first 40 residues of the amyloid protein was detected by circular dichroism (CD) in aqueous solution and with IRRAS at the interface. A stable /1-sheet-enriched state of the amyloid is formed at the air-water interface, in contrast to the initial bulk solution containing high a-helix/random coil and low /l-sheet parts. The change in the pH going from bulk (alkaline pH) to the interface (neutral or slightly acidic pH) can have effects on the conformation at the interface. Another alternative might be the intrinsic hydrophobicity of the air-water interface, which is a hydrophobic-hydrophilic system with air as the hydrophobic part. 

In 2001, the antimalarial drug quinacrine and the antipsychotic drug chlorpro-mazine (Fig. 1.14) were shown to inhibit prion infection in cells. Pmsiner and coworkers [24] identified the drugs independently, and found that they inhibited the conversion of normal prion protein into infectious prions, and also cleared prions from infected cells. Both drugs can cross over from the bloodstream to the brain, where the prion diseases are localized. 

M. Horiuchi, S. A. Priola, J. Chabry, et al. Interactions between heterologous fortms of prion protein binding, inhibition of conversion, and species barriers. Proceedings of the Society of National Academy of Sciences (USA) 97,5836 (2000). 

Prion Protein and Its Conformational Conversion A Structural Perspective... 

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