Fungal gasdermin-like proteins are controlled by proteolytic cleavage

Abstract

Gasdermins are a family of pore-forming proteins controlling an inflammatory cell death reaction in the mammalian immune system. The pore-forming ability of the gasdermin proteins is released by proteolytic cleavage with the removal of their inhibitory C-terminal domain. Recently, gasdermin-like proteins have been discovered in fungi and characterized as cell death-inducing toxins in the context of conspecific non-self-discrimination (allorecognition). Although functional analogies have been established between mammalian and fungal gasdermins, the molecular pathways regulating gasdermin activity in fungi remain largely unknown. Here, we characterize a gasdermin-based cell death reaction controlled by the het-Q allorecognition genes in the filamentous fungus Podospora anserina We show that the cytotoxic activity of the HET-Q1 gasdermin is controlled by proteolysis. HET-Q1 loses a ∼5-kDa C-terminal fragment during the cell death reaction in the presence of a subtilisin-like serine protease termed HET-Q2. Mutational analyses and successful reconstitution of the cell death reaction in heterologous hosts (Saccharomyces cerevisiae and human 293T cells) suggest that HET-Q2 directly cleaves HET-Q1 to induce cell death. By analyzing the genomic landscape of het-Q1 homologs in fungi, we uncovered that the vast majority of the gasdermin genes are clustered with protease-encoding genes. These HET-Q2-like proteins carry either subtilisin-like or caspase-related proteases, which, in some cases, correspond to the N-terminal effector domain of nucleotide-binding and oligomerization-like receptor proteins. This study thus reveals the proteolytic regulation of gasdermins in fungi and establishes evolutionary parallels between fungal and mammalian gasdermin-dependent cell death pathways.

Keywords: fungi; gasdermin; innate immunity; proteolysis; regulated cell death.