Assembly mechanism of the AIM2 inflammasome sensorrevealed by single-molecule analysis

Abstract

Pathogenic dsDNA prompts AIM2 (Absent In Melanoma 2) assembly leading to the formation of the inflammasome, a multimeric complex that triggers the inflammatory response. The recognition of foreign dsDNA involves AIM2 self-assembly concomitant with dsDNA binding. However, we lack mechanistic and kinetic information on the formation and propagation of the assembly, which can shed light on innate immunitys time response and specificity. Using correlative optical traps and fluorescence microscopy, we determine here the association and dissociation rates of the AIM2-DNA complex at the single-molecule level. We identify distinct mechanisms for oligomer growth via the binding of incoming AIM2 molecules to adjacent dsDNA or direct interaction with bound AIM2 assemblies, thus resembling primary and secondary nucleation processes. Through these mechanisms, AIM2 oligomers increase at least fourfold their size in seconds. Finally, our data indicate that single AIM2 molecules do not diffuse/scan along the DNA, suggesting that oligomerization depends on stochastic encounters with DNA and/or DNA-bound AIM2 molecules.