Summary L eucine R ich R epeat K inase 2 ( LRRK2 ) is the most commonly mutated gene in familial Parkinson’s disease (PD) 1 and is also linked to its idiopathic form 2 . LRRK2 is proposed to function in membrane trafficking 3 and co-localizes with microtubules 4 . Despite LRRK2’s fundamental importance for understanding and treating PD, there is limited structural information on it. Here we report the 3.5Å structure of the catalytic half of LRRK2, and an atomic model of microtubule-associated LRRK2 built using a reported 14Å cryo-electron tomography in situ structure 5 . We propose that the conformation of LRRK2’s kinase domain regulates its microtubule interaction, with a closed conformation favoring oligomerization on microtubules. We show that the catalytic half of LRRK2 is sufficient for filament formation and blocks the motility of the microtubule-based motors kinesin-1 and cytoplasmic dynein-1 in vitro . Kinase inhibitors that stabilize an open conformation relieve this interference and reduce LRRK2 filament formation in cells, while those that stabilize a closed conformation do not. Our findings suggest that LRRK2 can act as a roadblock for microtubule-based motors and have implications for the design of therapeutic LRRK2 kinase inhibitors.

AIM2 recognizes foreign dsDNA and assembles into the inflammasome, a filamentous supramolecular signalling platform required to launch innate immune responses. We show here that the pyrin domain of AIM2 (AIM2PYD) drives both filament formation and dsDNA binding. In addition, the dsDNA-binding domain of AIM2 also oligomerizes and assists in filament formation. The ability to oligomerize is critical for binding dsDNA, and in turn permits the size of dsDNA to regulate the assembly of the AIM2 polymers. The AIM2PYD oligomers define the filamentous structure, and the helical symmetry of the AIM2PYD filament is consistent with the filament assembled by the PYD of the downstream adaptor ASC. Our results suggest that the role of AIM2PYD is not autoinhibitory, but generating a structural template by coupling ligand binding and oligomerization is a key signal transduction mechanism in the AIM2 inflammasome.

The AIM2-ASC inflammasome is a filamentous signaling platform essential for mounting host defense against cytoplasmic dsDNA arising not only from invading pathogens but also from damaged organelles. Currently, the design principles of its underlying signaling network remain poorly understood at the molecular level. We show here that longer dsDNA is more effective in inducing AIM2 assembly, its self-propagation, and downstream ASC polymerization. This observation is related to the increased probability of forming the base of AIM2 filaments, and indicates that the assembly discerns small dsDNA as noise at each signaling step. Filaments assembled by receptor AIM2, downstream ASC, and their joint complex all persist regardless of dsDNA, consequently generating sustained signal amplification and hysteresis. Furthermore, multiple positive feedback loops reinforce the assembly, as AIM2 and ASC filaments accelerate the assembly of nascent AIM2 with or without dsDNA. Together with a quantitative model of the assembly, our results indicate that an ultrasensitive digital circuit drives the assembly of the AIM2-ASC inflammasome.