Structural mechanisms for ATP-mediated inhibition of human NLRP6 inflammasome.

Abstract

Inflammasomes ignite innate immune defense in response to infectious pathogens and noninfectious dangers, primarily through sensors composed of nucleotide-binding domain (NBD), leucine-rich repeat (LRR)-containing (NLR) family proteins. NLRP6 is an inflammasome sensor that plays critical roles in regulating intestinal inflammation, and its overactivation is linked to autoinflammatory diseases such as inflammatory bowel disease. However, how NLRP6 is maintained in an inhibited structure is unknown. Here we report two cryogenic-electron microscopy structures of human NLRP6 monomer in the adenosine-5'-triphosphate (ATP)/NBD-bound (twisted conformation) and unbound (extended conformation) states. The ATP-binding event connects and compacts the NACHT subdomains and the LRR domain, thus maintaining NLRP6 in an inhibitory conformation. NBD interacts directly with helical domain 1, winged-helix domain and helical domain 2, further contributing to the autoinhibition. Disruption of ATP binding and NBD interactions unleashes the NLRP6 inflammasome activation in the cellular study. The structural comparison between twisted and extended conformations reveals that the rearrangement of an NLRP6-specific acidic loop modulates NLRP6 activity. Although ATP-binding of NLRP6 and MCC950 (a potent NLRP3 inhibitor)-binding of NLRP3 share a similar interaction location in the structures, MCC950 does not inhibit NLRP6 in cells. Together, our data reveal the ATP-mediated cooperative inhibition mechanism of NLRP6 and provide insight into the therapeutic intervention of NLRP6-related autoinflammatory disorders.