Abstract:
Conversion of the cellular isoform of prion
protein (PrPc) into the scrapie isoform (PrPSc) involves an
increase in the /3-sheet content, diminished solubility, and
resistance to proteolytic digestion. Transgenetic studies argue
that PrPc and PrPSc form a complex during PrPScformation;
thus, synthetic PrP peptides, which mimic the conformational
pluralism of PrP, were mixed with PrPc to determine whether
its properties were altered. Peptides encompassing two a-helical
domains of PrP when mixed with PrPc produced a
complex that displayed many properties of PrPSc. The PrPcpeptide
complex formed fibrous aggregates and up to 65% of
complexed PrPc sedimented at 100,000 x g for 1 h, whereas
PrPc alone did not. These complexes were resistant to pro
teolytic digestion and displayed a high /3-sheet content. Un
expectedly, the peptide in a /3-sheet conformation did not form
the complex, whereas the random coil did. Addition of 2%
Sarkosyl disrupted the complex and rendered PrPc sensitive
to protease digestion. While the pathogenic AllTV mutation
increased the efficacy of complex formation, anti-PrP mono
clonal antibody prevented interaction between PrPc and pep
tides. Our findings in concert with transgenetic investigations
argue that PrPc interacts with PrPSc through a domain that
contains the first two putative a-helices. Whether PrPc-peptide
complexes possess prion infectivity as determined by
bioassays remains to be established.