Theme and variations: evolutionary diversification of the HET-s functional amyloid motif

Asen Daskalov 1 Witold Dyrka 2, 1, 3 Sven J Saupe 1
2 MAGNOME - Models and Algorithms for the Genome
Inria Bordeaux - Sud-Ouest, UB - Université de Bordeaux, CNRS - Centre National de la Recherche Scientifique : UMR5800
Abstract : In mammals and fungi, Nod-like receptors (NLR) activate downstream cell death execution proteins by a prion-like mechanism. In Podospora anserina, the NWD2 NLR activates the HET-S Helo-domain pore-forming protein by converting its prion-forming domain into a characteristic β-solenoid amyloid fold. The amyloid forming region of HET-S/s comprises two repetitions of a 21 amino acid motif. Herein, we systematically analyze the sequences of C-terminal regions of fungal HeLo and HeLo-like domain proteins to identify HET-s-related amyloid motifs (HRAM). We now identify four novel HRAM subfamilies in addition to the canonical HET-S/s subfamily. These novel motifs share the pseudo-repeat structure of HET-S/s and a specific pattern of distribution of hydrophobic and polar residues. Sequence co-variance analyses predict parallel in-register β-stacking of the two repeats and residue-residue interactions compatible with the β-solenoid fold. As described for HET-S, most genes encoding the HeLo proteins are adjacent to genes encoding NLRs also displaying HRAMs. The motifs of the NLRs are similar to those of their cognate HeLo-domain protein, indicating concerted evolution between repeats. This study shows that HET-s-related amyloid motifs are more common than anticipated and that they have diversified into discrete subfamilies that apparently share a common overall fold. Amyloids are self-templating protein polymers assembled by stacking of β-strands 1. Amyloid formation is often associated with disease, in particular neurodegenerative age-related pathologies such as Alzheimer's or Parkinson's diseases or other conditions like type 2 diabetes 2,3. Amyloid formation has also been linked to cancer with a proposed role of p53 amyloids in tumorogenesis 4. Yet, amyloids also fulfill a range of different functions inside and outside cells 5–7. Such so-called functional amyloids are involved in hormone and toxin storage and release, formation of cell surface structures in microorganisms and scaffolding of pigment synthesis. A role in the regulation of cell states is also described in yeast, where prion amyloids behave as epigenetic regulatory switches 8. Recently, it has also been reported that functional amyloids play a role in cell fate controlling sig-naling cascades both in mammals and fungi. In mammals, the RIP1 and RIP3 kinases which control the necroptosis cell death pathway form an amyloid-like complex assembled via short conserved motifs termed RHIM (for RIP homotypic interaction motifs) 9
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Scientific Reports, Nature Publishing Group, 2015, 5, pp.12494. 〈http://www.nature.com/articles/srep12494〉. 〈10.1038/srep12494〉
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Asen Daskalov, Witold Dyrka, Sven J Saupe. Theme and variations: evolutionary diversification of the HET-s functional amyloid motif. Scientific Reports, Nature Publishing Group, 2015, 5, pp.12494. 〈http://www.nature.com/articles/srep12494〉. 〈10.1038/srep12494〉. 〈hal-01202835〉

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