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Copper induces increased beta-sheet content in the scrapie-susceptible ovine prion protein PrPVRQ compared with the resistant allelic variant PrPARR.

ABSTRACT: 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. Results are presented here that show PrPVRQ and PrPARR display different conformational responses to metal-ion interaction. At 37 degrees C copper induced different levels of b-sheet content in the allelic variants of ovine full-length prion protein (amino acid 25-232). PrPVRQ showed a significant increase in b-sheet content when exposed to copper at 37 degrees C, whereas PrPARR remained relatively unchanged. The conversion of a-helical PrPVRQ to b-sheet form was shown by CD spectroscopy and the decreased binding of C-terminal specific monoclonal anti-PrP antibodies. This conversion to an increased b-sheet form did not occur with truncated PrPVRQ (amino acids 89-233), which demonstrates that additional metal-binding sites outside of the N-terminus may not overtly influence the overall structure of ovine PrP. Despite the difference in b-sheet content, both the scrapie-susceptible and -resistant allelic forms of ovine PrP acquired resistance to proteinase K digestion following exposure to copper at 37 degrees C, suggesting the potential for disease-associated PrPARR to accumulate in vivo. Our present study demonstrates that allelic variants of ovine PrP differ in their structure and response to the interaction with copper. These observations will contribute to a better understanding of the mechanism of susceptibility and resistance to prion disease.

SUBMITTER: Wong E

PROVIDER: S-EPMC1224157 | biostudies-other | 2004 May

REPOSITORIES: biostudies-other

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Project description:BackgroundA study to investigate transmission of classical scrapie via goat milk was carried out in sheep: firstly, lambs were challenged orally with goat scrapie brain homogenate to confirm transmission of scrapie from goats to sheep. In the second study phase, milk from scrapie-infected goats was fed to lambs. Lambs were selected according to their prion protein gene (PRNP) genotype, which was either VRQ/VRQ or ARQ/ARQ, with or without additional polymorphisms at codon 141 (FF141, LF141 or LL141) of the ovine PRNP. This report describes the clinical, pathological and molecular phenotype of goat scrapie in those sheep that progressed to clinical end-stage.ResultsTen sheep (six VRQ/VRQ and four ARQ/ARQ, of which three FF141 and one LL141) challenged with one of two scrapie brain homogenates, and six pairs of sheep (ARQ, of which five LL141 and seven LF141) fed milk from six different goats, developed clinical disease, which was characterised by a pruritic (all VRQ/VRQ and LL141 sheep) or a non-pruritic form (all LF141 and FF141 sheep). Immunohistochemical (IHC) examination revealed that the pattern of intra- and extracellular accumulation of disease-associated prion protein in the brain was also dependent on PRNP polymorphisms at codon 141, which was similar in VRQ and LL141 sheep but different from LF141 and FF141 sheep. The influence of codon 141 was also seen in discriminatory Western blot (WB), with LF141 and FF141 sheep showing a bovine spongiform encephalopathy-like profile (diminished reactivity with P4 antibody) on brain tissue. However, discriminatory WB in lymphoid tissues, and IHC pattern and profile both in lymphoid and brain tissue was consistent with classical scrapie in all sheep.ConclusionsThis study provided further evidence that the clinical presentation and the pathological and molecular phenotypes of scrapie in sheep are influenced by PRNP polymorphisms, particularly at codon 141. Differences in the truncation of disease-associated prion protein between LL141 sheep and those carrying the F141 allele may be responsible for these observations.

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Copper induces increased beta-sheet content in the scrapie-susceptible ovine prion protein PrPVRQ compared with the resistant allelic variant PrPARR.

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