HET-S (97% identical to HET-s) has an N-terminal globular domain that exerts a prion-inhibitory effect in cis on its own prion-forming domain (PFD) and in trans on HET-s prion propagation. We show that HET-S fails to form fibrils in vitro and that it inhibits HET-s PFD fibrillization in trans. In vivo analyses indicate that β-structuring of the HET-S PFD is required for HET-S activity. The crystal structures of the globular domains of HET-s and HET-S are highly similar, comprising a helical fold, while NMR-based characterizations revealed no differences in the conformations of the PFDs. We conclude that prion inhibition is not encoded by structure but rather in stability and oligomerization properties: when HET-S forms a prion seed or is incorporated into a HET-s fibril via its PFD, the β-structuring in this domain induces a change in its globular domain, generating a molecular species that is incompetent for fibril growth.
Highlights
► HET-S inhibits its own fibril formation as well as that of HET-s ► The structures of the N-terminal domains of HET-S and HET-s are very similar ► The prion inhibition mechanism relies on the stability of the N-terminal domain
