Peptidoglycan-Sensing Receptors Trigger the Formation of Functional Amyloids of the Adaptor Protein Imd to Initiate Drosophila NF-κB Signaling

Abstract

SUMMARY In the Drosophila immune response, bacterial derived diaminopimelic acid-type peptidoglycan binds the receptors PGRP-LC and PGRP-LE, which through interaction with the adaptor protein Imd leads to activation of the NF-κB homolog Relish and robust antimicrobial peptide gene expression. PGRP-LC, PGRP-LE, and Imd each contain a motif with some resemblance to the RIP Homotypic Interaction Motif (RHIM), a domain found in mammalian RIPK proteins forming functional amyloids during necroptosis. Here we found that despite sequence divergence, these Drosophila cryptic RHIMs formed amyloid fibrils in vitro and in cells. Amyloid formation was required for signaling downstream of Imd, and in contrast to the mammalian RHIMs, was not associated with cell death. Furthermore, amyloid formation constituted a regulatable step and could be inhibited by Pirk, an endogenous feedback regulator of this pathway. Thus, diverse sequence motifs are capable of forming amyloidal signaling platforms, and the formation of these platforms may present a regulatory point in multiple biological processes.

Reversible, functional amyloids: towards an understanding of their regulation in yeast and humans

“…Gain of toxicity and/or loss of function can lead to: -Neurodegeneration (Ross et al, Aguzzi et al 2010) -Systemic amyloidosis ( Features characterizing protein aggregates. Physiological and pathological protein aggregates are very diverse and multifaceted, and may be categorized based on features like structure [5,8,9,13,15,21,22,38,44], function [1,2,5,8,9,12,13,[23][24][25][26][44][45][46], reversibility [5][6][7][8][9], infectivity [27][28][29][30][31], localization [5,8,15,[32][33][34]47] and composition [5,35,36].…”

The RHIM within the M45 protein from murine cytomegalovirus forms heteromeric amyloid fibrils with RIPK1 and RIPK3

“…In 2012 Wu and colleagues demonstrated that the RHIM-driven association between RIPK1 and RIPK3 results in the formation of an amyloid, fibrillar structure where the RHIM residues form the β-sheet core of RIPK1:RIPK3 fibrils 29 . This necrosome complex was the first functional amyloid structure described with an active signalling role 30 but with the report of similar amyloid-based signalling platform in Drosophila , where the PGRP-LC and PGRP-LE receptors and downstream Imd adapter protein interact through motifs bearing some similarity to RHIMs 31 , RHIM-based signalling may be widespread. The structure of the necrosome RIPK1:RIPK3 core has now been determined by solid state nuclear magnetic resonance spectroscopy (ssNMR), revealing a compact hydrophobic interface and highlighting the central role of the RHIM tetrad 32 .…”

“…This necrosome complex was the first functional amyloid structure described with an active signalling role 30 . The report of a similar amyloid-based signalling platform in Drosophila , where the PGRP-LC and PGRP-LE receptors and downstream Imd adapter protein interact through motifs bearing some similarity to RHIMs 31 , suggests that RHIM-based signalling may be widespread. The structure of the necrosome RIPK1:RIPK3 core has been determined by solid-state nuclear magnetic resonance spectroscopy (ssNMR), confirming the hetero-amyloid nature of the complex and revealing a compact hydrophobic interface involving the RHIM tetrad 32 .…”

Identification of NLR-associated amyloid signaling motifs in filamentous bacteria

“…Metazoan or Metazoan viruses (El-Gebali et al 2018;Kajava et al 2014;Kleino et al 2017;Li et al 110 2012;Pham et al 2019). A few hits (24/286) however occur in Bacteria.…”

“…Finally, the PP-motif (for pseudo-palindrome) was described in Chaetomium 64 globosum and displays a sequence similarity with the mammalian RHIM amyloid sequence 65 scaffolding the RIP1K/RIP3K necrosome Li et al 2012;Sun et al 2002). RHIM 66 and RHIM-related motifs were also identified in viruses and Drosophila (Kleino et al 2017;Pham et 67 al. 2019).…”