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The bank vole (BV) prion protein (PrP) can function as a universal acceptor of prions. However, the molecular details of BVPrP's promiscuity for replicating a diverse range of prion strains remain obscure. To develop a cultured cell paradigm capable of interrogating the unique properties of BVPrP, we generated monoclonal lines of CAD5 cells lacking endogenous PrP but stably expressing either hamster (Ha), mouse (Mo), or BVPrP (M109 or I109 polymorphic variants) and then challenged them with various strains of mouse or hamster prions. Cells expressing BVPrP were susceptible to both mouse and hamster prions, whereas cells expressing MoPrP or HaPrP could only be infected with species‐matched prions. Propagation of mouse and hamster prions in cells expressing BVPrP resulted in strain adaptation in several instances, as evidenced by alterations in conformational stability, glycosylation, susceptibility to anti‐prion small molecules, and the inability of BVPrP‐adapted mouse prion strains to infect cells expressing MoPrP. Interestingly, cells expressing BVPrP containing the G127V prion gene variant, identified in individuals resistant to kuru, were unable to become infected with prions. Moreover, the G127V polymorphic variant impeded the spontaneous aggregation of recombinant BVPrP. These results demonstrate that BVPrP can facilitate cross‐species prion replication in cultured cells and that a single amino acid change can override the prion‐permissive nature of BVPrP. This cellular paradigm will be useful for dissecting the molecular features of BVPrP that allow it to function as a universal prion acceptor. [ABSTRACT FROM AUTHOR]

The protein-only hypothesis predicts that infectious mammalian prions are composed solely of PrPSc, a misfolded conformer of the normal prion protein, PrPC. However, protein-only PrPSc preparations lack significant levels of prion infectivity, leading to the alternative hypothesis that cofactor molecules are required to form infectious prions. Here, we show that prions with parental strain properties and full specific infectivity can be restored from protein-only PrPSc in vitro. The restoration reaction is rapid, potent, and requires bank vole PrPC substrate, post-translational modifications, and cofactor molecules. To our knowledge, this represents the first report in which the essential properties of an infectious mammalian prion have been restored from pure PrP without adaptation. These findings provide evidence for a unified hypothesis of prion infectivity in which the global structure of protein-only PrPSc accurately stores latent infectious and strain information, but cofactor molecules control a reversible switch that unmasks biological infectivity. [ABSTRACT FROM AUTHOR]

Previous studies identified prion protein (PrP) mutants which act as dominant negative inhibitors of prion formation through a mechanism hypothesized to require an unidentified species-specific cofactor termed protein X. To study the mechanism of dominant negative inhibition in vitro, we used recombinant PrPC molecules expressed in Chinese hamster ovary cells as substrates in serial protein misfolding cyclic amplification (sPMCA) reactions. Bioassays confirmed that the products of these reactions are infectious. Using this system, we find that: (1) trans-dominant inhibition can be dissociated from conversion activity, (2) dominant-negative inhibition of prion formation can be reconstituted in vitro using only purified substrates, even when wild type (WT) PrPC is pre-incubated with poly(A) RNA and PrPSc template, and (3) Q172R is the only hamster PrP mutant tested that fails to convert into PrPSc and that can dominantly inhibit conversion of WT PrP at sub-stoichiometric levels. These results refute the hypothesis that protein X is required to mediate dominant inhibition of prion propagation, and suggest that PrP molecules compete for binding to a nascent seeding site on newly formed PrPSc molecules, most likely through an epitope containing residue 172. [ABSTRACT FROM AUTHOR]

The article focuses on the functions of prion proteins. Prions could have both beneficial and harmful effects on cells. There is a need to study mammalian model systems to study the pathogenesis of clinical prion disease. A method has been devised to identify new anti-prion drugs using a yeast-based screen.

The structural conversion of a host protein, PrPC, into a protease-resistant isoform, PrPres, is the central event in the pathogenesis of infectious prion diseases. Purification of native PrPC molecules from hamster brain by either cation exchange or immobilized chelator chromatographic resins yielded preparations that supported efficient amplification of scrapie-induced PrPres in vitro. Using these purified preparations, we determined that in vitro PrPres amplification was inhibited by CuCl2 and ZnCl2 at IC50 concentrations of ∼400 nm and 10 μm, respectively. In contrast, 100 μm MnCl2 did not directly inhibit PrPres amplification or block Cu2+-mediated inhibition. Additionally, the inhibition of PrPres amplification by Cu2+ ions could be reversed by addition of either neocuproine or imidazole. Cu2+ inhibited PrPres amplification in both the presence and absence of stimulatory polyanion molecules. These biochemical findings support the hypothesis that Cu2+ ions might regulate the pathogenesis of prion diseases in vivo. [ABSTRACT FROM AUTHOR]

The article provides information related to a study on restriction of strain properties in purified prions. According to the study, Cofactor molecules can help in maintaining infectious conformation and restricting strain properties in prions. It informs that prions are formed by the misfolding of a normal cellular prion protein. It concludes that cofactor molecules play an essential role in determining the characteristics of mammalian prions including their infectivity andc structure.

The cofactor preferences for in vitro propagation of the protease-resistant isoforms of the prion protein (PrPSc) from various rodent species were investigated using the serial protein misfolding cyclic amplification (sPMCA) technique. Whereas RNA molecules facilitate hamster PrP propagation. RNA and several other polyanions do not promote the propagation of mouse and vole PrPSc molecules. Pretreatment of crude Prnp0/0 (PrP knockout) brain homogenate with RNase A or micrococcal nuclease inhibited hamster but not mouse PrPSc propagation in a reconstituted system. Mouse PrPSc propagation could be reconstituted by mixing PrPC substrate with homogenates prepared from either brain or liver, but not from several other tissues that were tested. These results reveal species-specific differences in cofactor utilization for PrPSc propagation in vitro and also demonstrate the existence of an endogenous cofactor present in brain tissue not composed of nucleic acids. [ABSTRACT FROM AUTHOR]

Little is currently known about the biochemical mechanism by which induced prion protein (PrP) conformational change occurs during mammalian prion propagation. In this study, we describe the reconstitution of PrPres amplification in vitro using partially purified and synthetic components. Overnight incubation of purifled PrP27-30 and PrPC molecules at a molar ratio of 1:250 yielded ∼2-fold baseline PrPres amplification. Addition of various polyanionic molecules increased the level of PrPres amplification to ∼10-fold overall. Polyanionic compounds that stimulated purified PrPres amplification to varying degrees included synthetic, homopolymeric nucleic acids such as poly(A) and poly(dT), as well as non-nucleic acid polyanions, such as heparan sulfate proteoglycan. Size fractionation experiments showed that synthetic poly(A) polymers must be > 0.2 kb in length to stimulate purified PrPres amplification. Thus, one possible set of minimal components for efficient conversion of PrP molecules in vitro may be surprisingly simple, consisting of PrP27-30, PrPC, and a stimulatory polyanionic compound. [ABSTRACT FROM AUTHOR]

A fundamental event in the pathogenesis of prion disease is the conversion of PrPC, a normal glycophosphatidyl-anchored glycoprotein, into an infectious isoform designated PrPSc. In a modified version of the protein misfolding cyclic amplification (PMCA) technique [Saborio et al. (2001) Nature 411, 810- 813], protease-resistant PrPSc-like molecules (PrPres) can be amplified in vitro in a species- and strain-specific manner from crude brain homogenates, providing a biochemical model of the prion conversion reaction [Lucassen et al. (2003) Biochemistry 42, 4127-4135]. In this study, we investigated the ability of enriched membrane subsets and detergent-solubilized membrane preparations to support PrPres amplification. Membrane fractionation experiments showed that purified synaptic plasma membrane preparations enriched in PrPC but largely depleted of late endosomal and lysosomal markers were sufficient to support PrPres amplification. Detergent solubilization experiments showed that a small group of select detergents could be used to produce soluble preparations that contain PrPC and fully support PrPres amplification. The stability of PrPres amplification ability in detergent-solubilized supernatants was dependent on detergent concentration. These results lead to the surprising conclusion that membrane attachment is not required for PrPC to convert efficiently into PrPres in vitro and also indicate that biochemical purification of PrPres amplification factors from brain homogenates is a feasible approach. [ABSTRACT FROM AUTHOR]

Chronic wasting disease (CWD) of cervids is associated with conversion of the normal cervid prion protein, PrPC, to a protease-resistant conformer, PrPCWD. Here we report the use of both nondenaturing amplification and protein-misfolding cyclic amplification (PMCA) to amplify PrPCWDin vitro. Normal brains from deer, transgenic mice expressing cervid PrPC [Tg(cerPrP)1536 mice], and ferrets supported amplification. PMCA using normal Tg(cerPrP)1536 brains as the PrPC substrate produced >6.5 x 109-fold amplification after six rounds. Highly efficient in vitro amplification of PrPCWD is a significant step toward detection of PrPCWD in the body fluids or excreta of CWD-susceptible species. [ABSTRACT FROM AUTHOR]