Argonaute proteins use single-stranded RNA or DNA guides to target complementary nucleic acids. This allows eukaryotic Argonaute proteins to mediate RNA interference and long prokaryotic Argonaute proteins to interfere with invading nucleic acids. The function and mechanisms of the phylogenetically distinct short prokaryotic Argonaute proteins remain poorly understood. Short prokaryotic Argonaute and the associated TIR-APAZ (SPARTA) proteins form heterodimeric complexes. Upon guide RNA-mediated target DNA binding, four SPARTA heterodimers form oligomers in which TIR domain-mediated NAD(P)ase activity is unleashed. When expressed in Escherichia coli, SPARTA is activated in the presence of highly transcribed multicopy plasmid DNA, which causes cell death through NAD(P)+ depletion. SPARTA can be repurposed for the programmable detection of DNA sequences. SPARTA as a prokaryotic immune system that reduces cell viability upon RNA-guided detection of invading DNA. Here you can see a cryoEM structure of Monomeric MapSPARTA bound with guide RNA and target DNA hybrid from Maribacter polysiphoniae (PDB code: 8SQU)

#molecularart .. #immolecular .. #sparta ... #argonaute ... #nadp ... #celldeath ... #cryoem

Structure rendered with @proteinimaging and depicted with @corelphotopaint