Key Discovery
Researchers from the University of Surrey and the University of Oxford have identified that inducible nitric oxide synthase (iNOS), a protein known for producing nitric oxide during inflammation, also binds directly to the protein IRG1 inside mitochondria. This physical interaction prevents IRG1 from producing itaconate, a metabolite that suppresses inflammation.
Methodology
The interaction was confirmed using co-immunoprecipitation and mass spectrometry in living cells. Computational modeling and molecular dynamics simulations predicted the interaction structure, and surface plasmon resonance confirmed stable, high-affinity binding in both mouse and human models. The interaction was not observed with the related protein eNOS, indicating specificity.
Key Results
- Cells lacking iNOS produced over 15 times more itaconate after immune stimulation than normal cells.
- iNOS mutants that could not produce nitric oxide still suppressed IRG1; suppression depended on iNOS adopting a specific shape stabilized by its cofactor tetrahydrobiopterin (BH4). Disrupting BH4 binding abolished the effect.
- Without iNOS, IRG1 associated with different partner proteins involved in glycolysis and cell metabolism, suggesting iNOS sequesters IRG1 from other metabolic roles.
Implications
The study challenges the assumption that iNOS controls immune cell behavior only through nitric oxide production.
The physical interface between iNOS and IRG1 may be a potential target for drugs that disrupt the interaction, allowing natural anti-inflammatory mechanisms to function. This approach could offer more precise control over inflammation compared to current methods targeting iNOS's enzymatic products.
Funding
The research was funded by the British Heart Foundation. Results were published in Nature Metabolism.