Copper induces increased beta-sheet content in the scrapie-susceptible ovine prion protein Prp(VRQ) compared with the resistant allelic variant Prp(ARR)

摘要

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 (Val(136)/Arg(154)/Gln(171))]or PrPARQ [PrP(Ala(136)/Arg(154)/Gln(171))] animals show susceptibility to scrapie, whereas those that express Ala(136)/Arg(154)/Arg(171) (PrPARR) show resistance. Results are presented here that show PrPVRQ and PrPARR display different conformational responses to metal-ion interaction. At 37 degreesC copper induced different levels of beta-sheet content in the allelic variants of ovine full-length prion protein (amino acid 25-232). PrPVRQ showed a significant increase in beta-sheet content when exposed to copper at 37 degreesC, whereas Prp(ARR) remained relatively unchanged. The conversion of a-helical PrPVRQ to beta-sheet form was shown by CD spectroscopy and the decreased binding of C-terminal specific monoclonal anti-PrP antibodies. This conversion to an increased beta-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 beta-sheet content, both the scrapic-susceptible and -resistant allelic forms of ovine PrP acquired resistance to protemase K digestion following exposure to copper at 37 degreesC, 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.