Signal transduction by a fungal NOD-like receptor based on propagation of a prion amyloid fold.

Asen Daskalov,Denis Martinez,Sven J Saupe,Raimon Sabaté,Alfons J M Debets,Birgit Habenstein,Antoine Loquet,Susan Lindquist

doi:10.1371/journal.pbio.1002059

Abstract

In the fungus Podospora anserina, the [Het-s] prion induces programmed cell death by activating the HET-S pore-forming protein. The HET-s β-solenoid prion fold serves as a template for converting the HET-S prion-forming domain into the same fold. This conversion, in turn, activates the HET-S pore-forming domain. The gene immediately adjacent to het-S encodes NWD2, a Nod-like receptor (NLR) with an N-terminal motif similar to the elementary repeat unit of the β-solenoid fold. NLRs are immune receptors controlling cell death and host defense processes in animals, plants and fungi. We have proposed that, analogously to [Het-s], NWD2 can activate the HET-S pore-forming protein by converting its prion-forming region into the β-solenoid fold. Here, we analyze the ability of NWD2 to induce formation of the β-solenoid prion fold. We show that artificial NWD2 variants induce formation of the [Het-s] prion, specifically in presence of their cognate ligands. The N-terminal motif is responsible for this prion induction, and mutations predicted to affect the β-solenoid fold abolish templating activity. In vitro, the N-terminal motif assembles into infectious prion amyloids that display a structure resembling the β-solenoid fold. In vivo, the assembled form of the NWD2 N-terminal region activates the HET-S pore-forming protein. This study documenting the role of the β-solenoid fold in fungal NLR function further highlights the general importance of amyloid and prion-like signaling in immunity-related cell fate pathways.

Highlights

Proteins that assemble into amyloids are responsible for a variety of human neurodegenerative pathologies [1,2]
The protein encoded by the gene adjacent to het-S is a Nod-like receptor (NLR) called NWD2
We show that NWD2 can template the formation of the [Het-s] prion fold in a ligand-controlled manner

Summary

Author Summary

Amyloids are best known as protein aggregates that are responsible for fatal neurodegenerative diseases, amyloid structures can fulfill functional roles in cells. The controlled formation of amyloid structures appears to be involved in different signaling processes in the context of programmed cell death and host defense. HET-S is a pore-forming protein that is activated when the [Het-s] prion causes its C-terminal domain to adopt an amyloid-like fold. NWD2 has an N-terminal motif homologous to the HET-S/s prion-forming region; we find that this region is both necessary and sufficient for its prion-inducing activity, and our functional and structural approaches reveal that the N-terminal region of NWD2 adopts a fold closely related to that of the HET-S/s prion. This study illustrates how the controlled formation of a prion amyloid fold can be used in a signaling process whereby a Nod-like receptor protein activates a downstream cell death execution domain

Introduction

Results

Discussion

Materials and Methods