LPS binding caspase activation and recruitment domains (CARDs) are bipartite lipid binding modules

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Caspase-11 acts as a pattern recognition receptor (PRR) detecting cytosolic bacterial lipopolysaccharides (LPS).
• It recognizes both non-self (bacterial LPS) and self-lipids, raising questions about shared recognition mechanisms.
• Caspase-11 triggers pyroptosis, a form of inflammatory cell death.

Purpose of the Study:

• To investigate the molecular mechanisms by which caspase-11's caspase activation and recruitment domain (CARD) interacts with self and non-self lipids.
• To determine if common or distinct regions within the CARD are responsible for binding different lipid types.
• To explore the potential for engineering novel lipid-binding domains based on conserved structural features.

Main Methods:

• Biochemical assays to analyze lipid-protein interactions.
• Computational modeling to understand binding interfaces.
• Cell-based assays to assess functional consequences of lipid binding.
• Protein engineering approaches using ancestral domains.

Main Results:

• The caspase-11 CARD functions as a bipartite lipid-binding module, with distinct regions interacting with phosphate groups and acyl chains.
• Both self and non-self lipids bind to specific sites within the CARD.
• Self-lipid binding is evolutionarily conserved across caspase-11 homologs and orthologs.
• An LPS-binding domain was successfully engineered *de novo* from an ancestral fish CARD-like domain.

Conclusions:

• The findings reveal a conserved molecular basis for lipid recognition by caspase-11, involving a bipartite binding module.
• The study highlights the intricate relationship between self and non-self lipid discrimination in innate immunity.
• Engineering of a novel LPS-binding domain demonstrates the potential for manipulating PRR function based on evolutionary insights.