Heparan Sulfate and Heparin Promote Faithful Prion Replication in Vitro by Binding to Normal and Abnormal Prion Proteins in Protein Misfolding Cyclic Amplification

The precise mechanism underlying the conversion of normal prion protein (PrP C ) into abnormal prion protein (PrP Sc ) remains unclear. Protein misfolding cyclic amplification (PMCA), an in vitro technique used for amplifying PrP Sc , results in PrP Sc replication that preserves the strain-specific characteristics of the input PrP Sc ; thus, PMCA mimics the process of in vivo PrP Sc replication. Previous work has demonstrated that in PMCA, nucleic acids are critical for PrP Sc amplification, but little information has been reported on glycosaminoglycan (GAG) participation in PrP Sc replication in vitro . Here, we investigated whether GAGs play a role in the faithful replication of PrP Sc by using a modified PMCA performed with baculovirus-derived recombinant PrP (Bac-PrP) as a substrate. The addition of heparan sulfate (HS) or its analog heparin (HP) restored the conversion efficiency in PMCA that was inhibited through nucleic acid depletion. Moreover, the PMCA products obtained under these conditions were infectious and preserved the properties of the input PrP Sc . These data suggest that HS and HP play the same role as nucleic acids in facilitating faithful replication of prions in PMCA. Furthermore, we showed that HP binds to both Bac-PrP and Bac-PrP Sc through the sulfated groups present on HP and that the N-terminal domain of Bac-PrP Sc might potentially not be involved in the binding to HP. These results suggest that the interaction of GAGs such as HS and HP with PrP C and/or PrP Sc through their sulfate groups is critical for the faithful replication of prions.