The polymorphisms at amino acid residues 136, 154, and 171 in ovine prion protein (PrP) have been associated with different susceptibility to scrapie: animals expressing PrP(ARQ) [PrP(Ala136/Arg154/Gln171)] show vulnerability, whereas those that express PrP(ARR) [PrP(Ala136/Arg154/Arg171)] are resistant to scrapie. The aim of this study was to evaluate the in vitro toxic effects of PrP(ARR) and PrP(ARQ) variants in relation with their structural characteristics. We show that both peptides cause cell death inducing apoptosis but, unexpectedly, the scrapie resistant PrP(ARR) form was more toxic than the scrapie susceptible PrP(ARQ) variant. Moreover, the alpha-helical conformation of PrP(ARR) was less stable than that of PrP(ARQ) and the structural determinants responsible of these different conformational stabilities were characterized by spectroscopic analysis. We observed that PrP toxicity was inversely related to protein structural stability, being the unfolded conformation more toxic than the native one. However, the PrP(ARQ) variant displays a higher propensity to form large aggregates than PrP(ARR). Interestingly, in the presence of small amounts of PrP(ARR), PrP(ARQ) aggregability was reduced to levels similar to that of PrP(ARR). Thus, in contrast to PrP(ARR) toxicity, scrapie transmissibility seems to reside in the more stable conformation of PrP(ARQ) that allows the formation of large amyloid fibrils.
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Different structural stability and toxicity of PrP(ARR) and PrP(ARQ) sheep prion protein variants.
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Department of Scienze degli Alimenti, Veterinary School, University of Teramo, Teramo, Italy.
The polymorphisms at amino acid residues 136, 154, and 171 in ovine prion protein (PrP) have been associated with different susceptibility to scrapie: animals expressing PrP(ARQ) [PrP(Ala136/Arg154/Gln171)] show vulnerability, whereas those that express PrP(ARR) [PrP(Ala136/Arg154/Arg171)] are resistant to scrapie. The aim of this study was to evaluate the in vitro toxic effects of PrP(ARR) and PrP(ARQ) variants in relation with their structural characteristics. We show that both peptides cause cell death inducing apoptosis but, unexpectedly, the scrapie resistant PrP(ARR) form was more toxic than the scrapie susceptible PrP(ARQ) variant.
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Biochem J
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Department of Clinical Veterinary Medicine, Centre for Veterinary Science, University of Cambridge, Madingley Road, Cambridge CB3 OES, UK.
The distribution of prion infectivity and PrPSc between peripheral lymphoid tissues suggests their possible haematogenic spread during the progression of natural scrapie in susceptible sheep. Since ovine PBMCs (peripheral blood mononuclear cells) express PrPC, they have the potential to carry or harbour disease-associated forms of PrP. To detect the possible presence of disease-associated PrP on the surface of blood cells, an understanding is required of the conformations that normal ovine cell-surface PrPC may adopt.
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Biochem J
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Centre for Veterinary Science, Department of Clinical Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 OES, UK.
Prion diseases are characterized by conformational change in the copper-binding protein PrP (prion protein). Polymorphisms in ovine PrP at amino acid residues 136, 154 and 171 are associated with variation in susceptibility to scrapie. PrPVRQ [PrP(Val136/Arg154/Gln171)] or PrPARQ [PrP(Ala136/Arg154/Gln171)] animals show susceptibility to scrapie, whereas those that express Ala136/Arg154/Arg171 (PrPARR) show resistance.
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Vet Rec
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Institute of Animal Breeding and Genetics, School of Veterinary Medicine Hannover, Germany.
Genetic susceptibility to scrapie is associated with polymorphisms in three different codons of the ovine prion protein (PrP) gene (136, 154, 171). Studies of PrP genotypes linked to scrapie have revealed the resistance of homozygous PrPARR/PrPARR animals and the high risk of PrPVRQ/PrPVRQ and PrPvRQ/PrPARQ animals in scrapie-affected flocks. The selection of PrPARR/PrPARR genotypes may therefore provide a strategy for controlling clinical scrapie.
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J Gen Virol
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Department of Molecular Biology, DLO-Institute for Animal Science and Health (ID-DLO), Lelystad, The Netherlands.
Scrapie is a fatal neurodegenerative disease of sheep that belongs to the group of prion diseases found in humans and animals. The host encoded prion protein (PrP) plays a central role in the disease process. In the PrP genes of man, mice and sheep, polymorphisms have been found that are associated with disease susceptibility and pathogenesis.
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