Conservation of a Glycine-rich Region in the Prion Protein Is Required for Uptake of Prion Infectivity

Christopher F Harrison,Victoria A Lawson,Bradley M Coleman,Yong-Sun Kim,Colin L Masters,Roberto Cappai,Kevin J Barnham,Andrew F Hill

doi:10.1074/jbc.m109.093310

Christopher F Harrison, Victoria A Lawson + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m109.093310

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Abstract

Prion diseases are associated with the misfolding of the endogenously expressed prion protein (designated PrP(C)) into an abnormal isoform (PrP(Sc)) that has infectious properties. The hydrophobic domain of PrP(C) is highly conserved and contains a series of glycine residues that show perfect conservation among all species, strongly suggesting it has functional and evolutionary significance. These glycine residues appear to form repeats of the GXXXG protein-protein interaction motif (two glycines separated by any three residues); the retention of these residues is significant and presumably relates to the functionality of PrP(C). Mutagenesis studies demonstrate that minor alterations to this highly conserved region of PrP(C) drastically affect the ability of cells to uptake and replicate prion infection in both cell and animal bioassay. The localization and processing of mutant PrP(C) are not affected, although in vitro and in vivo studies demonstrate that this region is not essential for interaction with PrP(Sc), suggesting these residues provide conformational flexibility. These data suggest that this region of PrP(C) is critical in the misfolding process and could serve as a novel, species-independent target for prion disease therapeutics.

Highlights

IntroductionGXXXG motifs are found as protein-protein interaction sites in a wide variety of proteins, including the region of the amyloid precursor protein that contains the Alzheimer disease-associated A␤ peptide [8] where mutation of these glycine residues alters the toxic potential of A␤ [10]
As the glycine-rich region (GRR) contains a series of flexible residues within a region known to undergo a significant structural change in prion disease, from flexible disorder in PrPC to protease-resistant structure in PrPSc, we hypothesized that it may play a role in the process of prion infection
The hydrophobic region of PrP lies at the boundary of the structured region of PrPC [2], its presence in the protease-resistant core implies that it is structured in PrPSc (Fig. 1A) [3]

Summary

Introduction

GXXXG motifs are found as protein-protein interaction sites in a wide variety of proteins, including the region of the amyloid precursor protein that contains the Alzheimer disease-associated A␤ peptide [8] where mutation of these glycine residues alters the toxic potential of A␤ [10]. GRR Modulates Prion Infection certain artificial systems of unknown physiological relevance [11] This region contains more glycine residues than required in a classical GXXXG motif. As the GRR contains a series of flexible residues within a region known to undergo a significant structural change in prion disease, from flexible disorder in PrPC to protease-resistant structure in PrPSc, we hypothesized that it may play a role in the process of prion infection. We created single amino acid substitutions to alter the hydrophobicity and flexibility of GRR residues and to demonstrate that even relatively conservative mutations within the GRR have a drastic effect on the propagation of prion infectivity, providing evidence that this highly conserved region of PrP is a dominant modulating factor on prion infectivity

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