Directionality of PYD filament growth determined by the transition of NLRP3 nucleation seeds to ASC elongation

• Published in: Science advances 2022-05, Vol.8 (19), p.eabn7583
• Main Authors: Hochheiser, Inga V, Behrmann, Heide, Hagelueken, Gregor, Rodríguez-Alcázar, Juan F, Kopp, Anja, Latz, Eicke, Behrmann, Elmar, Geyer, Matthias
• Format: Article
• Language: English
• Subjects: Biomedicine and Life Sciences; Immunology; SciAdv r-articles; Structural Biology
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.abn7583

Inflammasomes sense intrinsic and extrinsic danger signals to trigger inflammatory responses and pyroptotic cell death. Homotypic pyrin domain (PYD) interactions of inflammasome forming nucleotide-binding oligomerization domain (NOD)-like receptors with the adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD) mediate oligomerization into filamentous assemblies. We describe the cryo-electron microscopy (cryo-EM) structure of the human NLRP3 filament and identify a pattern of highly polar interface residues that form the homomeric interactions leading to characteristic filament ends designated as A- and B-ends. Coupling a titration polymerization assay to cryo-EM, we demonstrate that ASC adaptor protein elongation on NLRP3 nucleation seeds is unidirectional, associating exclusively to the B-end of the filament. Notably, NLRP3 and ASC PYD filaments exhibit the same symmetry in rotation and axial rise per subunit, allowing a continuous transition between NLRP3 and ASC. Integrating the directionality of filament growth, we present a molecular model of the ASC speck consisting of active NLRP3, ASC, and Caspase-1 proteins.