GO:0070976 TIR domain binding: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0070976 (TIR domain binding) is a molecular function describing binding to the Toll/Interleukin-1 receptor (TIR) domain, a conserved protein-protein interaction module.
• TIR domains are found in Toll-like receptors (TLRs), interleukin-1 receptors (IL-1Rs), and the adaptor MyD88, and they mediate innate immune signal transduction.
• Beyond immune signaling, TIR domains can act as enzymes: plant TIR proteins synthesize 2',3'-cAMP/cGMP to trigger cell death, and bacterial TIR proteins produce histidine-ADPR as an immune signal.
• SARM1, a TIR-domain protein, senses dsDNA and promotes NAD+ degradation and cell death, linking TIR domain binding to neurodegeneration and axon degeneration.
• TIR domain binding is central to plant immunity, where helper NLRs are activated by TIR immune signaling, and substrate-induced condensation regulates plant TIR activity.
• Studying TIR domain binding requires integrated structural, biochemical, and CRISPR-based approaches to dissect interactions and disease relevance.
Description
TIR domain binding (GO:0070976) is a molecular function that refers to the binding of a protein to a Toll/Interleukin-1 receptor (TIR) domain. The TIR domain is an intracellular protein-protein interaction module of approximately 200 residues found in Toll-like receptors (TLRs), interleukin-1 receptors (IL-1Rs), and the adaptor protein MyD88. This domain contains three highly conserved regions and is essential for transmitting signals from activated receptors to downstream effectors in innate immunity. Researchers study TIR domain binding to understand how immune signaling is initiated and regulated, and how mutations or dysregulation contribute to disease. The importance of TIR domain binding extends beyond classical immunity. Recent studies have revealed that TIR domains can also possess enzymatic activities, such as synthesizing cyclic nucleotides or producing novel immune signals, thereby expanding their functional repertoire [5,7]. For example, plant TIR domain proteins act as 2',3'-cAMP/cGMP synthetases to mediate cell death, and bacterial TIR domains produce histidine-ADPR as an immune signal. These discoveries highlight the dual role of TIR domains in both binding and catalysis. In this article, we provide a comprehensive overview of TIR domain binding, covering its definition, biological significance, key genes, regulatory mechanisms, disease associations, and research methodologies. We emphasize how CRISPR-based models can be used to dissect the causal roles of TIR domain-containing proteins in health and disease.
TIR domain binding At A Glance
| GO ID | GO:0070976 |
|---|---|
| GO term | TIR domain binding |
| Ontology | molecular_function |
| Synonym | Toll-Interleukin receptor domain binding |
| Major function | Binding to a TIR domain to mediate protein-protein interactions in immune signaling and related processes |
| Domain structure | TIR domain is ~200 residues with three highly conserved regions |
| Found in | Toll protein, IL-1R, MyD88, and other TIR-containing proteins |
| Related activity | Some TIR domains exhibit enzymatic activities such as cyclic nucleotide synthesis or ADPR transfer [5,7] |
What Is GO:0070976?
TIR domain binding is the molecular function of selectively interacting with a TIR domain in a target protein. The TIR domain itself is a conserved 200-amino-acid domain present in Toll-like receptors, interleukin-1 receptors, and the adaptor MyD88. It contains three highly conserved regions that facilitate protein-protein interactions between TLRs and signal-transduction components. Thus, GO:0070976 describes the binding event that enables assembly of signaling complexes and, in some cases, enzymatic activation.
Why Is TIR domain binding Important in Cell Biology?
TIR domain binding is a cornerstone of innate immune signaling and is increasingly implicated in diverse biological processes, including cell death, neurodegeneration, and plant immunity. Understanding this function at the molecular level can reveal how pathogens evade immunity, how chronic inflammation arises, and how to design targeted therapeutics. Moreover, the discovery of enzymatic activities within TIR domains has opened new avenues for research into small-molecule modulators [4,5,7].
• Mediates signal transduction from TLRs and IL-1Rs to downstream adaptors, initiating inflammatory and antimicrobial responses.
• Mutations in TIR domain-containing proteins are linked to immune disorders and cancer.
• SARM1 TIR domain activity drives NAD+ depletion and axon degeneration, a hallmark of neurodegenerative diseases.
• Plant TIR domain proteins produce cyclic nucleotides to trigger hypersensitive cell death, a model for immunity.
• Bacterial TIR domains generate histidine-ADPR, revealing a novel immune signaling molecule.
• TIR domain binding is a target for small-molecule inhibitors, as shown for SARM1.
• Helper NLR activation by TIR signaling in plants provides insights into conserved immune mechanisms.
• Substrate-induced condensation regulates plant TIR activity, linking phase separation to immune function.
• Interleukin-36, which signals through TIR-domain-containing receptors, is important in inflammatory diseases.
• CRISPR screens can identify novel regulators of TIR domain binding and downstream pathways.
Molecular Mechanism of TIR domain binding
TIR Domain Structure and Interaction Interfaces
In simple terms: The TIR domain is a protein module that acts like a plug, allowing proteins to connect and pass signals.
The TIR domain is an intracellular domain of approximately 200 residues with three highly conserved regions (box 1, box 2, and box 3) that form the interaction surface. It is found in Toll-like receptors, interleukin-1 receptors, and the adaptor MyD88, and it mediates protein-protein interactions between TLRs and signal-transduction components. Structural studies of SARM1, a TIR-domain protein, have revealed the architecture of the TIR domain and its role in substrate recognition and activation.
Binding-Induced Assembly of Signaling Complexes
In simple terms: When TIR domains bind to each other, they form a platform that recruits downstream proteins to start a signal.
TIR domain binding facilitates the assembly of signaling complexes, such as the myddosome, where multiple TIR domains interact to recruit kinases and initiate downstream cascades. In plants, TIR domain proteins can form oligomers or condensates upon substrate binding, which activates their enzymatic function. Similarly, bacterial TIR domains assemble to produce histidine-ADPR as an immune signal.
Enzymatic Activities of TIR Domains
In simple terms: Some TIR domains are not just connectors; they can also act as enzymes that make signaling molecules.
Beyond binding, certain TIR domains possess enzymatic activities. Plant TIR domains function as 2',3'-cAMP/cGMP synthetases, generating cyclic nucleotides that mediate cell death. Bacterial TIR domains produce histidine-ADPR, a novel immune signal. SARM1 TIR domain catalyzes NAD+ degradation, leading to axonal degeneration. These activities are often triggered by binding events, such as substrate-induced condensation.
Regulation by Substrate and Condensation
In simple terms: The activity of TIR domains can be switched on when they bind to specific molecules and clump together.
Substrate-induced condensation has been shown to activate plant TIR domain proteins, linking phase separation to immune signaling. In SARM1, activation involves structural changes and substrate recognition, which can be inhibited by small molecules. Helper NLR activation by plant and bacterial TIR immune signaling further illustrates the regulatory complexity.
TIR Domain Binding in Disease and Immunity
In simple terms: When TIR domain binding goes wrong, it can lead to diseases like neurodegeneration or autoimmunity.
Dysregulation of TIR domain binding is implicated in neurodegenerative diseases through SARM1-mediated NAD+ depletion. In plants, TIR domain signaling is critical for immunity against pathogens. Interleukin-36, which signals via TIR-domain-containing receptors, plays a role in inflammatory diseases. These examples underscore the broad pathophysiological relevance of TIR domain binding.
Key Genes Involved in GO:0070976 TIR domain binding
The following genes encode proteins that contain TIR domains or interact with them, and are central to research on GO:0070976.
| Gene | Major Role | Research Relevance |
|---|---|---|
| MYD88 | Adaptor protein with a TIR domain that mediates TLR/IL-1R signaling | Central to innate immunity; knockout models reveal signaling defects |
| TIRAP | TIR domain-containing adaptor protein involved in TLR2 and TLR4 signaling | Links TLRs to MyD88; studied in inflammation |
| TRIF | TIR domain-containing adaptor inducing IFN-beta | Mediates MyD88-independent TLR signaling |
| TRAM | TIR domain-containing adaptor related to TRIF | Specific to TLR4 signaling |
| SARM1 | TIR domain protein that senses dsDNA and promotes NAD+ degradation | Implicated in axon degeneration and neurodegeneration |
| IL1R1 | Interleukin-1 receptor with a TIR domain | Key in inflammatory signaling |
| IL1RAP | IL-1 receptor accessory protein with TIR domain | Required for IL-1 signaling |
| TLR4 | Toll-like receptor 4 with a TIR domain | Recognizes LPS; model for innate immunity |
| TLR2 | Toll-like receptor 2 with a TIR domain | Recognizes bacterial lipoproteins |
| IL36R | Interleukin-36 receptor with TIR domain | Involved in skin inflammation |
| TIR1 | Plant TIR domain protein (not the auxin receptor) | Model for TIR enzymatic activity |
| RPS4 | Plant TIR-NB-LRR immune receptor | Studied in plant immunity |
| RRS1 | Plant TIR-NB-LRR immune receptor | Pairs with RPS4 for resistance |
| EDS1 | Plant helper NLR activated by TIR signaling | Central to plant immunity |
| NRG1 | Plant helper NLR | Activated by TIR signaling |
| ADPRC | Bacterial TIR domain protein producing histidine-ADPR | Novel immune signal discovery |
| SARM1 (human) | TIR domain enzyme | Target for small-molecule inhibitors |
How Is TIR domain binding Regulated?
TIR domain binding and downstream signaling are tightly regulated. In TLR/IL-1R pathways, negative regulators such as IRAK-M and SOCS proteins modulate signal strength. SARM1 activity is regulated by its autoinhibitory N-terminal domain and by substrate availability. In plants, TIR domain activity is controlled by substrate-induced condensation and by helper NLRs. Bacterial TIR signaling is regulated by the availability of substrates and interacting partners.
TIR domain binding and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SARM1 | Neurodegeneration, axon degeneration | Knockout and point-mutation models in neurons |
| MYD88 | Inflammatory diseases, cancer | Knockout mice and cell lines |
| IL36R | Psoriasis, inflammatory skin diseases | Knock-in and knockout models |
| TIR1 (plant) | Plant immunity | Plant knockout and overexpression lines |
| EDS1 (plant) | Plant immunity | Plant knockout and complementation |
Neurodegeneration and Axon Degeneration
SARM1, a TIR domain-containing protein, senses dsDNA and promotes NAD+ degradation, leading to cell death. Its TIR domain enzymatic activity is a key driver of axon degeneration in neurodegenerative diseases, making it a therapeutic target.
Inflammatory and Autoimmune Diseases
TIR domain binding is essential for IL-1 and IL-36 signaling, which are implicated in inflammatory disorders such as psoriasis and arthritis. Dysregulation of TLR signaling through TIR domain interactions can lead to chronic inflammation.
Plant Immunity and Crop Protection
Plant TIR domain proteins mediate immune responses against pathogens by producing cyclic nucleotides and activating helper NLRs [5,6]. Understanding TIR domain binding in plants can inform strategies for disease-resistant crops.
Bacterial Immune Signaling
Bacterial TIR domains produce histidine-ADPR as an immune signal, revealing a novel mechanism of bacterial defense. This may inspire new antimicrobial strategies.
From TIR domain binding-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of TIR domain binding abolish immune signaling? | Knockout of MYD88 or TIRAP in cell lines |
| Does a point mutation in the TIR domain affect binding affinity? | Point-mutation knock-in of SARM1 or TLR4 |
| Can a tagged TIR domain protein be used to pull down interactors? | Knock-in of FLAG- or HA-tagged TIR domain |
| Does overexpression of a TIR domain protein activate downstream pathways? | Overexpression of SARM1 or plant TIR proteins |
| What genes regulate TIR domain binding? | CRISPR library screening |
| How does substrate-induced condensation affect TIR activity? | Live-cell imaging of fluorescently tagged TIR proteins |
How to Study the TIR domain binding Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Cryo-EM | 3D structure of TIR domain complexes | Visualizing binding interfaces |
| Pull-down assay | Protein-protein interactions | Identifying TIR domain binding partners |
| Surface plasmon resonance (SPR) | Binding affinity and kinetics | Quantifying TIR domain interactions |
| NF-kB reporter assay | Downstream signaling activation | Functional validation of TIR domain binding |
| CRISPR knockout screening | Gene essentiality for TIR signaling | Discovering novel regulators |
| Live-cell imaging | Condensation and localization | Studying substrate-induced condensation |
| Enzymatic assays | Cyclic nucleotide or ADPR production | Measuring TIR enzymatic activity [5,7] |
Structural Biology (Cryo-EM, X-ray Crystallography)
Structural studies have elucidated the architecture of TIR domains and their interaction interfaces, as shown for SARM1. These methods reveal how binding occurs at the atomic level.
Biochemical Binding Assays (Pull-down, SPR, ITC)
In vitro binding assays can measure affinity and specificity of TIR domain interactions. For example, SARM1 TIR domain binding to substrates has been characterized biochemically.
Cell-Based Signaling Assays (Reporter Assays, NF-kB Activation)
Reporter assays are used to monitor downstream signaling upon TIR domain binding, such as NF-kB activation in TLR/IL-1R pathways.
CRISPR Screens and Functional Genomics
Genome-wide CRISPR screens can identify novel regulators of TIR domain binding and signaling. This approach is powerful for discovering genes that modulate immune responses.
How CRISPR Can Be Used to Study GO:0070976 TIR domain binding
Knockout
CRISPR knockout of TIR domain-containing genes (e.g., MYD88, SARM1) can abolish binding and downstream signaling, providing causal evidence for their role in immune responses and disease [1,2].
Point Mutation
Introducing point mutations in the TIR domain (e.g., in SARM1 or TLR4) can disrupt specific binding interfaces, allowing researchers to dissect the contribution of individual residues to TIR domain binding and signaling.
Knock-in
Knock-in of tagged TIR domain proteins (e.g., FLAG-SARM1) enables affinity purification and proteomic identification of binding partners, as well as live-cell imaging of localization.
Overexpression
Overexpression of TIR domain proteins can constitutively activate or inhibit signaling pathways, useful for gain-of-function studies and for testing small-molecule inhibitors [4,5].
How EDITGENE Supports TIR domain binding Research
Researchers studying TIR domain binding-related genes often need to determine whether a candidate gene is causally involved in a specific signaling pathway or disease phenotype. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models, enabling rigorous functional validation.
Contact EDITGENE today to design your custom CRISPR model for TIR domain binding research.
Frequently Asked Questions About TIR domain binding
What is TIR domain binding?
TIR domain binding (GO:0070976) is the molecular function of binding to a Toll/Interleukin-1 receptor (TIR) domain, a conserved protein module that mediates interactions in immune signaling.
What genes are involved in TIR domain binding?
Key genes include MYD88, TIRAP, TRIF, TRAM, SARM1, IL1R1, TLR4, and plant TIR genes like RPS4 and EDS1 [1,2,5,6].
What is the function of the TIR domain?
The TIR domain mediates protein-protein interactions between TLRs and signal-transduction components, and in some cases acts as an enzyme to produce signaling molecules [1,5,7].
Which diseases are associated with TIR domain binding?
Dysregulation is linked to neurodegeneration (SARM1), inflammatory diseases (IL-36), and plant immunity [2,6,8].
How can I study TIR domain binding?
Methods include structural biology, binding assays, cell-based signaling assays, and CRISPR screens [1,4].
What is the role of SARM1 in TIR domain binding?
SARM1 is a TIR domain protein that senses dsDNA and promotes NAD+ degradation, leading to cell death and neurodegeneration.
Can TIR domains act as enzymes?
Yes, plant TIR domains synthesize 2',3'-cAMP/cGMP, and bacterial TIR domains produce histidine-ADPR [5,7].
What is substrate-induced condensation in TIR signaling?
It is a process where substrate binding causes TIR proteins to condense, activating their enzymatic function.
How are TIR domain interactions regulated?
They are regulated by negative regulators, autoinhibitory domains, and substrate availability [1,4].
What CRISPR models are available for TIR domain research?
EDITGENE offers knockout, point mutation, knock-in, overexpression, and library screening services for TIR domain genes.
Conclusion
TIR domain binding (GO:0070976) is a fundamental molecular function that underpins innate immune signaling and extends to enzymatic activities with broad biological impact. From TLR/IL-1R pathways to plant immunity and neurodegeneration, TIR domain interactions are central to health and disease. Leveraging CRISPR-based models and advanced screening technologies will continue to unravel the complexities of TIR domain binding and facilitate therapeutic development.
References
- 1. Takeda K et al.. 2004. TLR signaling pathways.. Semin Immunol 16(1):3-9 PMID: 14751757
- 2. Wang L et al.. 2025. SARM1 senses dsDNA to promote NAD(+) degradation and cell death.. Cell 188(25):7137-7154.e21 PMID: 41138726
- 3. Song W et al.. 2024. Substrate-induced condensation activates plant TIR domain proteins.. Nature 627(8005):847-853 PMID: 38480885
- 4. Shi Y et al.. 2022. Structural basis of SARM1 activation, substrate recognition, and inhibition by small molecules.. Mol Cell 82(9):1643-1659.e10 PMID: 35334231
- 5. Yu D et al.. 2022. TIR domains of plant immune receptors are 2',3'-cAMP/cGMP synthetases mediating cell death.. Cell 185(13):2370-2386.e18 PMID: 35597242
- 6. Yu H et al.. 2024. Activation of a helper NLR by plant and bacterial TIR immune signaling.. Science 386(6728):1413-1420 PMID: 39509471
- 7. Sabonis D et al.. 2025. TIR domains produce histidine-ADPR as an immune signal in bacteria.. Nature 642(8067):467-473 PMID: 40307559
- 8. Zhou L et al.. 2021. Interleukin-36: Structure, Signaling and Function.. Adv Exp Med Biol 21:191-210 PMID: 32026417
