Significance The nucleotide-binding oligomerization domain (NOD)-like receptor pyrin domain containing 3 (NLRP3) is a pattern recognition receptor that forms an inflammasome. The cryo-electron microscopy structure of the dodecameric form of full-length NLRP3 bound to the clinically relevant NLRP3-specific inhibitor MCC950 has established the structural basis for the oligomerization-mediated regulation of NLRP3 inflammasome activation and the mechanism of action of the NLRP3 specific inhibitor. The inactive NLRP3 oligomer represents the NLRP3 resting state, capable of binding to membranes and is likely disrupted for its activation. Visualization of the inhibitor binding mode will enable optimization of the activity of NLRP3 inflammasome inhibitor drugs.

Nucleotide‐binding and oligomerisation domain‐like receptors (NLRs) can form inflammasomes that activate caspase‐1 and pro‐interleukin‐1β and induce pyroptosis. NLR family pyrin domain‐containing 9 (NLRP9) forms an inflammasome and activates innate immune responses during virus infection, but little is known about this process. Here, we report the crystal and cryo‐electron microscopy structures of NLRP9 in an ADP‐bound state, revealing inactive and closed conformations of NLRP9 and its similarities to other structurally characterised NLRs. Moreover, we found a C‐terminal region interacting with the concave surface of the leucine‐rich repeat domain of NLRP9. This region is unique among NLRs and might be involved in the specific function of NLRP9. These data provide the structural basis for understanding the mechanism of NLRP9 regulation and activation.