Identification of a novel cell death-inducing domain reveals that fungal amyloid-controlled programmed cell death is related to necroptosis

Abstract

Recent findings have revealed the role of prion-like mechanisms in the control of host defense and programmed cell death cascades. In fungi, HET-S, a cell death-inducing protein containing a HeLo pore-forming domain, is activated through amyloid templating by a Nod-like receptor (NLR). Here we characterize the HELLP protein behaving analogously to HET-S and bearing a new type of N-terminal cell death-inducing domain termed HeLo-like (HELL) and a C-terminal regulatory amyloid motif known as PP. The gene encoding HELLP is part of a three-gene cluster also encoding a lipase (SBP) and a Nod-like receptor, both of which display the PP motif. The PP motif is similar to the RHIM amyloid motif directing formation of the RIP1/RIP3 necrosome in humans. The C-terminal region of HELLP, HELLP(215-278), encompassing the motif, allows prion propagation and assembles into amyloid fibrils, as demonstrated by X-ray diffraction and FTIR analyses. Solid-state NMR studies reveal a well-ordered local structure of the amyloid core residues and a primary sequence that is almost entirely arranged in a rigid conformation, and confirm a β-sheet structure in an assigned stretch of three amino acids. HELLP is activated by amyloid templating and displays membrane-targeting and cell death-inducing activity. HELLP targets the SBP lipase to the membrane, suggesting a synergy between HELLP and SBP in membrane dismantling. Remarkably, the HeLo-like domain of HELLP is homologous to the pore-forming domain of MLKL, the cell death-execution protein in necroptosis, revealing a transkingdom evolutionary relationship between amyloid-controlled fungal programmed cell death and mammalian necroptosis.amyloid | prion | programmed cell death | incompatibility | necroptosis

On the evolutionary trajectories of signal-transducing amyloids in fungi and beyond

“…26 The PP amyloid motif was identified in a previous in silico search for putative signal transducing amyloids.…”

“…11,26 Two relatively well-conserved asparagine residues extend this sequence homology further, each flanking the pseudo-palindrome. The reported similarities relate even more the metazoan and fungal amyloid transducing domains.…”

“…First, the PP motif seems to be controlling several different effector domains, a situation not described for the HET-s PFD. 12,26 Indeed, a protein called SBP (SESB-PP), bearing a putative lipase (SESB) as an effector domain at its N-terminus, contains a functional PP motif. 26 The SBP encoding gene is a part of a 3 genes cluster in the genome of Chaetomium globosum, a species in the same order as P. anserina.…”

“…12,26 Indeed, a protein called SBP (SESB-PP), bearing a putative lipase (SESB) as an effector domain at its N-terminus, contains a functional PP motif. 26 The SBP encoding gene is a part of a 3 genes cluster in the genome of Chaetomium globosum, a species in the same order as P. anserina. The two other genes of the cluster encode a protein with a HeLo-like membranetargeting, cytotoxic domain fused to a PP motif and a PP-containing NLR protein.…”

“…The two other genes of the cluster encode a protein with a HeLo-like membranetargeting, cytotoxic domain fused to a PP motif and a PP-containing NLR protein. 26 The exclusive association of some effector domains with the PP motif may suggest a functional difference between PP and HET-s PFD. Different properties of the amyloid structures formed by the PP motif and the HET-s PFD, combined with constraints of the activity of the effector itself, could explain the observed domain assortments.…”