Activation of Thoeris antiviral system via SIR2 effector filament assembly.
Giedrė TamulaitienėDziugas SabonisGiedrius SasnauskasAudrone RuksenaiteArunas SilanskasCarmel AvrahamGal OfirRotem SorekMindaugas ZarembaVirginijus SiksnysPublished in: Nature (2024)
To survive bacteriophage (phage) infections, bacteria developed numerous anti-phage defence systems 1-7 . Some of them (for example, type III CRISPR-Cas, CBASS, Pycsar and Thoeris) consist of two modules: a sensor responsible for infection recognition and an effector that stops viral replication by destroying key cellular components 8-12 . In the Thoeris system, a Toll/interleukin-1 receptor (TIR)-domain protein, ThsB, acts as a sensor that synthesizes an isomer of cyclic ADP ribose, 1''-3' glycocyclic ADP ribose (gcADPR), which is bound in the Smf/DprA-LOG (SLOG) domain of the ThsA effector and activates the silent information regulator 2 (SIR2)-domain-mediated hydrolysis of a key cell metabolite, NAD + (refs. 12-14 ). Although the structure of ThsA has been solved 15 , the ThsA activation mechanism remained incompletely understood. Here we show that 1''-3' gcADPR, synthesized in vitro by the dimeric ThsB' protein, binds to the ThsA SLOG domain, thereby activating ThsA by triggering helical filament assembly of ThsA tetramers. The cryogenic electron microscopy (cryo-EM) structure of activated ThsA revealed that filament assembly stabilizes the active conformation of the ThsA SIR2 domain, enabling rapid NAD + depletion. Furthermore, we demonstrate that filament formation enables a switch-like response of ThsA to the 1''-3' gcADPR signal.