RIP2 filament formation is required for NOD2 dependent NF-κB signalling

Area of Science:

• Immunology
• Structural Biology
• Molecular Biology

Background:

• NOD2 (Nucleotide-binding oligomerization domain-containing protein 2) is a key pattern recognition receptor in the innate immune system.
• Activation of NOD2 by bacterial muramyl-dipeptide leads to the recruitment of RIP2 (Receptor-interacting protein kinase 2) and subsequent inflammatory signaling.
• Dysregulated NOD2 signaling is implicated in various inflammatory diseases.

Purpose of the Study:

• To elucidate the structural basis of RIP2 filament formation mediated by its CARD domain.
• To investigate the mechanism of NOD2-mediated nucleation of RIP2 filaments.
• To determine the role of RIP2 polymerization in NOD2-induced NF-κB activation and inflammatory cytokine production.

Main Methods:

• X-ray crystallography
• Solid-state Nuclear Magnetic Resonance (NMR)
• Cryo-electron microscopy (cryo-EM)
• Structure-guided mutagenesis

Main Results:

• Full-length RIP2 forms long filaments through its CARD domain.
• NOD2's tandem CARDs bind to the end of RIP2 filaments, enabling polar nucleation.
• The atomic structure of the helical RIP2 CARD filament reveals stabilizing intermolecular interactions.
• RIP2 polymerization is essential for NOD2-mediated NF-κB signaling activation.

Conclusions:

• Activated NOD2 initiates RIP2 filament polymerization, a critical step in innate immune signaling.
• The structure of the RIP2 CARD filament provides insights into immune complex assembly.
• Targeting RIP2 polymerization may offer novel therapeutic strategies for inflammatory conditions driven by aberrant NOD2 signaling.