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.