Inflammasome sensor NLRP1 disease variant M1184V promotes autoproteolysis and DPP9 complex formation by stabilizing the FIIND domain

The inflammasome sensor NLRP1 (nucleotide-binding olig-omerization domain-like receptor containing a pyrin domain 1) detects a variety of pathogen-derived molecular patterns to induce an inflammatory immune response by triggering pyroptosis and cytokine release. A number of mutations and polymorphisms of NLRP1 are known to cause autoinflammatory diseases, the functional characterization of which contributes to a better understanding of NLRP1 regulation. Here, we assessed the effect of the common NLRP1 variant M1184V, associated with asthma, inflammatory bowel disease, and diabetes, on the protein level. Our size-exclusion chromatography experiments show that M1184V stabilizes the function-to -find domain (FIIND) in a monomeric conformation. This effect is indepen-dent of autoproteolysis. In addition, molecular dynamics sim-ulations reveal that the methionine residue increases flexibility within the ZU5 domain, whereas valine decreases flexibility, potentially indirectly stabilizing the catalytic triad responsible for autocleavage. By keeping the FIIND domain monomeric, formation of a multimer of full-length NLRP1 is promoted. We found that the stabilizing effect of the valine further leads to improved dipeptidyl peptidase 9 (DPP9)-binding capacities for the FIIND domain as well as the full-length protein as deter-mined by surface plasmon resonance. Moreover, our immuno-precipitation experiments confirmed increased DPP9 binding for the M1184V protein in cells, consistent with improved for-mation of an autoinhibited complex with DPP9 in activity as-says. Collectively, our study establishes a molecular rationale for the dichotomous involvement of the NLRP1 variant M1184V in autoimmune syndromes.