SPECIFIC-INHIBITION OF IN-VITRO FORMATION OF PROTEASE-RESISTANT PRIONPROTEIN BY SYNTHETIC PEPTIDES

The transmissible spongiform encephalopathies are characterized by the conversion of the protease-sensitive prion protein (PrPsen) into a pr otease-resistant isoform (PrPres) associated with the neuropathogenic process in vivo. Recently, PrPres has been shown to be capable of dire ctly inducing the conversion of PrPsen to PrPres in a cell-free in vit ro system. In the present experiments, various PrP peptides were studi ed for their ability to enhance or inhibit this cell-free conversion r eaction. None of the synthetic peptides was able to confer protease-re sistance to the labeled PrPsen molecules on their own. On the contrary , peptides from the central part of the hamster PrP sequence from 106 to 141 could completely inhibit the conversion induced by preformed Pr Pres. The presence of residues 119 and 120 from the highly hydrophobic sequence AGAAAAGA (position 113 to 120) was crucial for an efficient inhibitory effect. Fourier transform infrared spectroscopy analysis in dicated that inhibitory peptides formed high P-sheet aggregates under the conditions of the conversion reaction, but this was also true of c ertain peptides that were not inhibitory. Thus, the potential to form P-sheeted aggregates may be necessary, but not sufficient, for peptide s to act as inhibitors of PrPres formation, Clearly, the amino acid se quence of the peptide is also important for inhibition. The sequence s pecificity of the inhibition is consistent with the idea that residues in the vicinity of positions 106-141 of PrPres and/or PrPsen are crit ically involved in the intermolecular interactions that lead to PrPres formation.