Cryo-EM structure of the activated NAIP2-NLRC4 inflammasome reveals nucleated polymerization

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Science  08 Oct 2015:
DOI: 10.1126/science.aac5789

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The NLR family apoptosis inhibitory proteins (NAIPs) bind conserved bacterial ligands, like the bacterial rod protein PrgJ, and recruit the NLR family CARD-containing protein 4 (NLRC4) as the inflammasome adapter to activate innate immunity. Here we show that the PrgJ-NAIP2-NLRC4 inflammasome is assembled into multisubunit disk-like structures through a unidirectional ATPase polymerization, primed with a single PrgJ-activated NAIP2 per disk. Cryo-electron microscopy (cryo-EM) reconstruction at a subnanometer resolution revealed a ~90° hinge rotation accompanying NLRC4 activation. Unlike in the related, heptameric Apaf-1 apoptosome in which each subunit needs to be conformationally activated by its ligand before assembly, a single PrgJ-activated NAIP2 initiates NLRC4 polymerization in a domino-like reaction to promote the disk assembly. These insights reveal the mechanism of signal amplification in NAIP/NLRC4 inflammasomes.

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