Identification of a short sequence motif in the influenza A virus pathogenicity factor PB1-F2 required for inhibition of human NLRP3


Influenza A virus infection activates the NLRP3 inflammasome, a multiprotein signalling complex responsible for the proteolytic activation and release of the proinflammatory cytokine IL-1β from monocytes and macrophages. Some influenza A virus (IAV) strains encode a short 90-amino acid peptide (PB1-F2) on an alternative open reading frame of segment 2, with immunomodulatory activity. The authors of this article, led by GCIR Professor Mirco Schmolke, recently demonstrated that contemporary IAV PB1-F2 inhibits the activation of NLRP3, potentially by NEK7-dependent activation. PB1-F2 binds to NLRP3 with its C-terminal 50 amino acids, but the exact binding motif was unknown. On the NLRP3 side, the interface is formed through the leucine-rich-repeat (LRR) domain, potentially in conjunction with the pyrin domain. Here, they took advantage of PB1-F2 sequences from IAV strains with either weak or strong NLRP3 interaction. Sequence comparison and structure prediction using Alphafold2 identified a short four amino acid sequence motif (TQGS) in PB1-F2 that defines NLRP3-LRR binding. Conversion of this motif to that of the non-binding PB1-F2 suffices to lose inhibition of NLRP3 dependent IL-1β release. The TQGS motif further alters the subcellular localization of PB1-F2 and its colocalization with NLRP3 LRR and pyrin domain. Structural predictions suggest the establishment of additional hydrogen bonds between the C-terminus of PB1-F2 and the LRR domain of NLRP3, with two hydrogen bonds connecting to threonine and glutamine of the TQGS motif. Phylogenetic data show that the identified NLRP3 interaction motif in PB1-F2 is widely conserved among recent IAV-infecting humans. These data explain at a molecular level the specificity of NLRP3 inhibition by influenza A virus.

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Why is it important?

Influenza A virus infection triggers a robust inflammatory response and high fever. This response is crucial for the efficient elimination of the virus by the human immune system. One key player in this inflammatory response is the signal protein IL-1b, which is released from inflammatory macrophages. Its production and release rely on the proper functioning of multiprotein signalling complex, the NLRP3 inflammasome. Previous research from this lab revealed that influenza A virus hampers NLRP3 activation through a viral inhibitor called PB1-F2. In this study, the authors delve deeper into how this short peptide interacts with NLRP3. They identified a specific molecular interaction involving four amino acids in PB1-F2 that is essential for inhibiting the human immune response mediated by NLRP3. This insight could lead to the development of targeted therapies aimed at disrupting this interaction and enhancing the immune response against influenza A virus infections.

5 Apr 2024