An N-terminal CDC42 T43I variant reveals the mechanism of pyrin inflammasome activation.

Heterozygous carboxyl-terminal variants in the RHO guanosine triphosphatase (GTPase) CDC42 are known to cause severe autoinflammatory syndromes. Here, we identified a heterozygous amino-terminal p.T43I (Thr43→Ile) CDC42 variant in patients with autoinflammation and uncovered a molecular link between CDC42 and the inflammasome sensor pyrin, mutated in the hereditary autoinflammatory syndrome familial Mediterranean fever. We demonstrate that the region surrounding residue T43 of CDC42 interacts with the carboxyl-terminal B30.2 domain of pyrin and regulates its localization and activation. The p.T43I substitution strengthens the CDC42-pyrin interaction through additional van der Waals interactions, leading to increased pyrin inflammasome activation, as evidenced by increased ASC (apoptosis-associated speck-like protein containing a caspase activating and recruitment domain) speck formation, enhanced pyroptosis, and excessive interleukin-1β (IL-1β) and IL-18 production. These findings identify CDC42 as a pyrin ligand and provide critical insights into the role of the pyrin B30.2 domain in inflammasome activation, suggesting dual regulation of pyrin by two RHO family GTPases, RHOA and CDC42.