Structural Evolution of TIR-Domain Signalosomes

Area of Science:

• Molecular Biology
• Immunology
• Biochemistry

Background:

• Toll/interleukin-1 receptor/resistance (TIR) domains are vital components of innate immunity in eukaryotes.
• TIR domains mediate signaling through transient self-association and interactions with other TIR domains.
• Recent findings reveal TIR domains also function as catalytic enzymes, particularly in NAD+-nucleosidase activity within cell-death pathways.

Purpose of the Study:

• To review and compare the structures, interactions, and functional roles of TIR domain-containing proteins in eukaryotic immunity.
• To elucidate the distinct mechanisms of TIR domain assembly and signaling in scaffolding versus enzymatic functions.
• To highlight how these distinct roles lead to varied innate immunity and cell-death outcomes.

Main Methods:

• Review of existing literature on TIR domain-containing proteins.
• Structural analysis of TIR domain assemblies.
• Comparison of interaction interfaces and signaling mechanisms.

Main Results:

• TIR domain signalosomes form two distinct structural groups: scaffold and enzyme assemblies.
• Both assemblies feature open-ended, two-stranded complexes but differ in strand orientation.
• Functional specificity arises from the nature of TIR:TIR interactions within these distinct assemblies.

Conclusions:

• TIR domain interactions dictate distinct signaling pathways, leading to specific innate immunity and cell-death responses.
• Understanding these structural and functional differences is key to comprehending innate immune regulation and cell fate.
• The dual role of TIR domains as scaffolds and enzymes offers insights into complex cellular processes.