Cryo-EM structures of the active NLRP3 inflammasome disc

Inflammasomes are cytosolic innate immune complexes that activate caspase-1 following detection of pathogenic and endogenous dangers(1-5), and NACHT-, leucine-rich repeat (LRR)-and pyrin domain (PYD)-containing protein 3 (NLRP3) is an inflammasome sensor of membrane damage highly important in regard to the induction of inflammation(2,6,7). Here we report cryogenic electron microscopy structures of disc-shaped active NLRP3 oligomers in complex with adenosine 5 '-O-(3-thio)triphosphate, the centrosomal NIMA-related kinase 7 (NEK7) and the adaptor protein ASC, which recruits caspase-1. In these NLRP3-NEK7-ASC complexes, the central NACHT domain of NLRP3 assumes an ATP-bound conformation in which two of its subdomains rotate by about 85 degrees relative to the ADP-bound inactive conformation(8-12). The fish-specific NACHT-associated domain conserved in NLRP3 but absent in most NLRPs13 becomes ordered in its key regions to stabilize the active NACHT conformation and mediate most interactions in the disc. Mutations on these interactions compromise NLRP3-mediated caspase-1 activation. The N-terminal PYDs from all NLRP3 subunits combine to form a PYD filament that recruits ASC PYD to elicit downstream signalling. Surprisingly, the C-terminal LRR domain and the LRR-bound NEK7 do not participate in disc interfaces. Together with previous structures of an inactive NLRP3 cage in which LRR-LRR interactions play an important role8-11, we propose that the role of NEK7 is to break the inactive cage to transform NLRP3 into the active NLRP3 inflammasome disc.