Filament assembly confers the mechanical resilience of the IFI16 restrictosome

Interferon-inducible protein 16 (IFI16) is a mammalian innate immune sensor composed of a filament-forming pyrin domain (PYD) followed by tandem HIN200 domains that bind nucleic acids. First recognized as a major regulator of inflammatory responses against cytosolic double-stranded (ds)DNA, IFI16 filaments have been implicated in several key mechanical processes involving both host and pathogens, including viral replication restriction, latency regulation, replication-stress responses, and DNA-damage responses. Moreover, IFI16 filaments are ultra-stable, a key trait believed to drive its autoantigenicity. Although recent studies reported that IFI16 undergoes liquid-liquid phase separation (LLPS) via disordered linkers and multivalent protein-dsDNA interactions, whether such a metastable entity provides a framework for the mechanical activities of IFI16 remains unknown. Here, we show that PYD-driven filament assembly confers the mechanical stability of IFI16 condensates by compacting DNA into ultra-stable tangles capable of withstanding forces sufficient to induce duplex deformation. By contrast, HIN200-dsDNA complexes are much more sensitive to ionic perturbation, DNA pretension, and mechanical interference. Together, we demonstrate that filament assembly allows IFI16 to act as a mechano-sensitive restrictor.