Argonaute proteins recruit small (∼15–30 nucleotide [nt]) single-stranded guide oligonucleotides to bind complementary single-stranded target sequences. Eukaryotic Argonaute proteins (eAgos) use guide RNAs to bind and/or cleave target RNA, a process that underlies RNA interference (RNAi) . Prokaryotes encode homologs of eAgos (pAgos) but lack other proteins required for RNAi. Most characterized pAgos share a fixed four-domain composition (N-PAZ-MID-PIWI) with eAgos. These “long” pAgos interfere with the invading nucleic acids (NAs), such as plasmids, and bacteriophages. Long pAgos have also been implicated in genome decatenation and stimulation of homologous recombination. In contrast to eAgos, certain long pAgos utilize single-stranded (ss)DNA guides to target invading DNA sequences. Short prokaryotic Ago accounts for most prokaryotic Argonaute proteins (pAgos) and is involved in defending bacteria against invading nucleic acids. Short pAgo associated with TIR-APAZ (SPARTA) has been shown to oligomerize and deplete NAD+ upon guide-mediated target DNA recognition. However, the molecular basis of SPARTA inhibition and activation remains unknown. Here you can see a cryoEM structure reported by Guo et al (doi.org/10.1038/s41589-023-01478-0) of CrtSPARTA Octamer bound with guide-target (PDB code: 8JAY)

#molecularart ... #cryoem ... #crtSPARTA ... #argonaute

Structure rendered with @proteinimaging, post-processed with @stylar.ai_official and depicted with @corelphotopaint