Mouse Prion Protein (PrP) Segment 100 to 104 Regulates Conversion of PrP C to PrP Sc in Prion-Infected Neuroblastoma Cells

Prion diseases are characterized by the replicative propagation of disease-associated forms of prion protein (PrPSc ; PrP refers to prion protein). The propagation is believed to proceed via two steps; the initial binding of the normal form of PrP (PrPC ) to PrPSc and the subsequent conversion of PrPC to PrPSc . We have explored the two-step model in prion-infected mouse neuroblastoma (ScN2a) cells by focusing on the mouse PrP (MoPrP) segment 92-GGTHNQWNKPSKPKTN-107, which is within a region previously suggested to be part of the binding interface or shown to differ in its accessibility to anti-PrP antibodies between PrPC and PrPSc . Exchanging the MoPrP segment with the corresponding chicken PrP segment (106-GGSYHNQKPWKPPKTN-121) revealed the necessity of MoPrP residues 99 to 104 for the chimeras to achieve the PrPSc state, while segment 95 to 98 was replaceable with the chicken sequence. An alanine substitution at position 100, 102, 103, or 104 of MoPrP gave rise to nonconvertible mutants that associated with MoPrPSc and interfered with the conversion of endogenous MoPrPC . The interference was not evoked by a chimera (designated MCM2) in which MoPrP segment 95 to 104 was changed to the chicken sequence, though MCM2 associated with MoPrPSc . Incubation of the cells with a synthetic peptide composed of MoPrP residues 93 to 107 or alanine-substituted cognates did not inhibit the conversion, whereas an anti-P8 antibody recognizing the above sequence in PrPC reduced the accumulation of PrPSc after 10 days of incubation of the cells. These results suggest the segment 100 to 104 of MoPrPC plays a key role in conversion after binding to MoPrPSc .