Identification of a homology-independent linchpin domain controlling mouse and bank vole prion protein conversion

Cassandra M Burke,Abigail B Diack,Alexander D Steele,Jean C Manson,Joel C Watts,Surachai Supattapone,Kenneth M K Mark,Geoffrey P Noble,Daniel J Walsh,Sabine Gilch

doi:10.1371/journal.ppat.1008875

Abstract

Prions are unorthodox pathogens that cause fatal neurodegenerative diseases in humans and other mammals. Prion propagation occurs through the self-templating of the pathogenic conformer PrPSc, onto the cell-expressed conformer, PrPC. Here we study the conversion of PrPC to PrPSc using a recombinant mouse PrPSc conformer (mouse protein-only recPrPSc) as a unique tool that can convert bank vole but not mouse PrPC substrates in vitro. Thus, its templating ability is not dependent on sequence homology with the substrate. In the present study, we used chimeric bank vole/mouse PrPC substrates to systematically determine the domain that allows for conversion by Mo protein-only recPrPSc. Our results show that that either the presence of the bank vole amino acid residues E227 and S230 or the absence of the second N-linked glycan are sufficient to allow PrPC substrates to be converted by Mo protein-only recPrPSc and several native infectious prion strains. We propose that residues 227 and 230 and the second glycan are part of a C-terminal domain that acts as a linchpin for bank vole and mouse prion conversion.

Highlights

Prions are unorthodox infectious agents of fatal neurological diseases that affect many mammalian species, including humans
The results show that bank vole (BV) brain homogenate (BH), but not Ha BH or Mo BH, is capable of propagating Mo protein-only recPrPSc (Fig 1B, third column)
Mo BH is capable of propagating only RML, and Ha BH is capable of propagating only 139H (Fig 1B). These results show that BV PrP is a uniquely susceptible substrate to Mo protein-only recPrPSc and native prion strains from other species

Summary

Introduction

Prions are unorthodox infectious agents of fatal neurological diseases that affect many mammalian species, including humans. The central pathogenic event underlying prion infection is the self-propagating conformational change of a host-encoded glycoprotein (PrPC) into a misfolded conformer (PrPSc)[1]. The protein-only hypothesis states that infectious prions are composed solely of PrPSc[2, 3]. Much evidence indicates that cofactor molecules are required for the formation of infectious prions[4,5,6,7]. In direct support of this concept, our laboratory generated two selfpropagating bacterially-expressed recombinant (rec) PrPSc conformers (cofactor recPrPSc and protein-only recPrPSc) by propagating the same original seed in the presence and absence of purified phospholipids, respectively[7, 8]. Whereas cofactor recPrPSc effectively seeds mouse (Mo) brain homogenate (BH) sPMCA reactions in vitro and potently infects wild-type mice in vivo, protein-only recPrPSc cannot seed Mo BH sPMCA reactions and fails to infect wild-type mice[7]

Methods

Results

Discussion

Conclusion