Structural basis of RIP2 activation and signaling

Area of Science:

• Immunology
• Structural Biology
• Molecular Biology

Background:

• Pathogen recognition receptors (PRRs) detect bacterial infections.
• Receptor-interacting-serine/threonine-protein kinase 2 (RIPK2) is crucial for Nucleotide-binding-oligomerization-domain-containing proteins 1/2 (NOD1/NOD2) signaling.
• Dysregulation of this pathway impacts bacterial detection and can lead to autoimmune diseases.

Purpose of the Study:

• To investigate the structural basis of RIPK2 activation.
• To elucidate the mechanism of RIPK2 oligomerization upon NOD1/NOD2 stimulation.
• To understand how RIPK2 propagates signals in response to bacterial infections.

Main Methods:

• In vitro reconstitution of the RIPK2-CARD complex (RIPosome).
• Cryo-electron microscopy (cryo-EM) to determine the filament structure at 4.1 Å resolution.
• Structure-guided mutagenesis experiments at CARD-CARD interfaces.

Main Results:

• The Caspase-activation-and-recruitment-domain (CARD) of RIPK2 (RIP2-CARD) forms oligomeric structures (RIPosome) upon stimulation by NOD1-CARD or NOD2-2CARD.
• The cryo-EM structure reveals the filament structure of the active RIP2-CARD complex.
• Mutagenesis studies identified key CARD-CARD interfaces involved in RIPK2 activation and self-propagation.

Conclusions:

• RIPK2 activation involves the formation of a self-propagating RIPosome filament.
• The structure provides insights into how NOD1/NOD2 CARD domains initiate RIPK2 oligomerization.
• Understanding RIPK2 activation mechanisms is critical for addressing defects in bacterial detection and autoimmune diseases.