NACHT, LRR and PYD domains-containing protein 3
NLRP3 inflammasome complex assembly
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<sup>1-5</sup>, 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<sup>2,6,7</sup>. 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° relative to the ADP-bound inactive conformation<sup>8-12</sup>. The fish-specific NACHT-associated domain conserved in NLRP3 but absent in most NLRPs<sup>13</sup> 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 role<sup>8-11</sup>, we propose that the role of NEK7 is to break the inactive cage to transform NLRP3 into the active NLRP3 inflammasome disc.