Protein misfolding cyclic amplification (PMCA) is an in vitro simulation of
prion replication, which relies on the use of normal brain homogenate derived from host species as substrate for the specific amplification of abnormal
prion protein, PrP(Sc). Studies showed that recombinant cellular PrP, PrP(C), expressed in Escherichia coli lacks N-glycosylation and an glycophosphatidyl
inositol anchor (GPI) and therefore may not be the most suitable substrate in seeded PMCA reactions to recapitulate
prion conversion in vitro. In this study, we expressed 2 PRNP genotypes of sheep, V136L141R154Q171 and A136F141R154Q171, and one genotype of white-tailed deer (Q95G96, X132,Y216) using the baculovirus expression system and evaluated their suitability as substrates in seeded-PMCA. It has been reported that host-encoded mammalian
RNA molecules and
divalent cations play a role in the pathogenesis of
prion diseases, and
RNA molecules have also been shown to improve the sensitivity of PMCA assays. Therefore, we also assessed the effect of co-factors, such as
prion-specific
mRNA molecules and a divalent
cation,
manganese, on
protein conversion. Here, we report that baculovirus-expressed recombinant PrP(C) shows a glycoform and GPI-anchor profile similar to mammalian brain-derived PrP(C) and supports amplification of PrP(Sc) and PrP(CWD) derived from
prion-affected animals in a single round of seeded PMCA in the absence of exogenous co-factors. Addition of species-specific in vitro transcribed PrP
mRNA molecules stimulated the conversion efficiency resulting in increased PrP(Sc) or PrP(CWD) production. Addition of 2 to 20 μM of
manganese chloride (MnCl2) to unseeded PMCA resulted in conversion of recombinant PrP(C) to
protease-resistant PrP. Collectively, we demonstrate, for the first time, that baculovirus expressed sheep and deer PrP can serve as a substrate in
protein misfolding cyclic amplification for sheep and deer
prions in the absence of additional exogenous co-factors.