3D atomic structure reveals evolution of prions in templated amplification in vitro

Introduction

Prions are proteinaceous infectious particles, which replicate by incorporating cellular prion protein into an amyloid structure. Biological and pathological properties of the prion, which define its strain characteristics, are determined by the specific amyloid fold in the prion fibril.

Objectives

The study aims to replicate authentic prions in vitro and to probe whether fibril structure and prion strain characteristics are altered or conserved in this environment.

Methods

We replicated murine RML, ME7 and 22L prions through multiple rounds of protein misfolding cyclic amplification (PMCA) using recombinant PrP substrate and analysed their structures and strain characteristics though multiparametric analysis including cell culture infectivity assays, mouse bioassays, spectral fingerprinting and, ultimately, 3D structural analysis by cryo-electron microscopy.

Results / conclusion

While amplified prions retained high infectivity titers in cell culture assays, we found that prion structures and biological strain properties mutated in the course of in vitro amplification, leading to a novel prion strain. Both structure and strain characteristics evolved to a prion, which is related to but distinct from RML. Interestingly, spectral fingerprinting suggested a convergence on similar prion structures independently of the initial prion seed. These findings suggest that replication environment is a major factor driving prion evolution.