Functionally Relevant Domains of the Prion Protein Identified In Vivo

Frank Baumann,Thomas Rülicke,Jens Pahnke,Juliane Bremer,Markus Tolnay,Ivan Radovanovic,Adriano Aguzzi

doi:10.1371/journal.pone.0006707

Abstract

The prion consists essentially of PrPSc, a misfolded and aggregated conformer of the cellular protein PrPC. Whereas PrPC deficient mice are clinically healthy, expression of PrPC variants lacking its central domain (PrPΔCD), or of the PrP-related protein Dpl, induces lethal neurodegenerative syndromes which are repressed by full-length PrP. Here we tested the structural basis of these syndromes by grafting the amino terminus of PrPC (residues 1–134), or its central domain (residues 90–134), onto Dpl. Further, we constructed a soluble variant of the neurotoxic PrPΔCD mutant that lacks its glycosyl phosphatidyl inositol (GPI) membrane anchor. Each of these modifications abrogated the pathogenicity of Dpl and PrPΔCD in transgenic mice. The PrP-Dpl chimeric molecules, but not anchorless PrPΔCD, ameliorated the disease of mice expressing truncated PrP variants. We conclude that the amino proximal domain of PrP exerts a neurotrophic effect even when grafted onto a distantly related protein, and that GPI-linked membrane anchoring is necessary for both beneficial and deleterious effects of PrP and its variants.

Highlights

PrPSc is the main constituent of prions [1], the infectious agents causing transmissible spongiform encephalopathies (TSE)
Neuronal expression of Dpl leads to ataxia, neuronal loss and demyelinating neuropathy [17,18,19,22] while most of the toxicity of truncated preparations of wild-type and anchorless PrP (PrPs) can be assigned to the lack of the central domain CD [10]
If the absence of a CD-like domain were responsible for its toxicity, addition of domains containing the CD region of PrP might detoxify Dpl

Summary

Introduction

PrPSc is the main constituent of prions [1], the infectious agents causing transmissible spongiform encephalopathies (TSE). Toxicity appears to correlate with partial or complete deletions of the conserved PrP central domain (CD, residues 94–134) [9,10,11] which bridges the flexible amino proximal tail and the globular carboxy proximal domain [12] Another neurotoxic phenotype was detected in compoundheterozygous Prnpo/ZHII mice and in homozygous PrnpZHII/ZHII mice [13] whose PrnpZHII allele leads to ectopic expression of the PrPCrelated protein Dpl [14,15,16,17]. We reported previously that the removal of just the CD domain confers dramatic neurotoxicity to PrP This suggests that the toxicity of Dpl may result from the absence of a CD-like domain. Removal of the GPI addition signal from PrPDCD prevents its neurotoxic effects

Results

Discussion

Materials and Methods