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[https://www.uniprot.org/uniprot/A0A316E3U6_9FLAO A0A316E3U6_9FLAO]  

While eukaryotic Argonautes and long prokaryotic Argonautes (pAgos) cleave nucleic acids, some short pAgos lack nuclease activity and hydrolyze NAD(P)(+) to induce bacterial cell death(1). We present a hierarchical activation pathway for SPARTA, a short pAgo consisting of an Ago protein and an associated protein TIR-APAZ(2). SPARTA progresses through distinct oligomeric forms, including a monomeric apo state, a monomeric RNA/DNA-bound state, two dimeric RNA/DNA-bound states, and a tetrameric RNA/DNA-bound active state. These snapshots together identify oligomerization as a mechanistic principle of SPARTA activation. Apo SPARTA is inactive, its RNA/DNA-binding channel occupied an auto-inhibitory motif in TIR-APAZ. Upon RNA/DNA binding, SPARTA transitions from a monomer to a symmetric and then an asymmetric dimer, in which two TIR domains interact via charge and shape complementarity. Next, two dimers assemble into a tetramer with a central TIR cluster responsible for hydrolyzing NAD(P)(+). Additionally, we observed unique features of SPARTA-RNA/DNA interactions, including competition between the DNA 3' end and the auto-inhibitory motif, interactions between the RNA G2 nucleotide and Ago, and splaying of the RNA-DNA duplex by two loops exclusive to short pAgos. Together, our findings contribute a mechanistic basis for the activation of short pAgos, a large section of the Ago superfamily.

Oligomerization-mediated activation of a short prokaryotic Argonaute.,Shen Z, Yang XY, Xia S, Huang W, Taylor DJ, Nakanishi K, Fu TM Nature. 2023 Jul 26. doi: 10.1038/s41586-023-06456-z. PMID:37494956<ref>PMID:37494956</ref>