Csx15 is a broad specificity ring nuclease bridging CRISPR-Cas and CBASS cyclic nucleotide signaling systems

Csx15, a CRISPR-associated protein family, is a broad specificity ring nuclease that degrades cyclic nucleotide signals from both CRISPR-Cas and CBASS pathways.

• Why it matters: CRISPR-Cas type III and CBASS both use cyclic nucleotides as second messengers, but their signaling is regulated differently, leaving the shared molecular control unclear.
• What they did: The study used structural and biochemical analyses to show Csx15 forms diverse oligomeric states, undergoes ligand-induced conformational transitions, and assembles filaments for catalytic activity.
• The result: Csx15 is linked to SAVED-domain effectors and is a close relative, suggesting Csx15-like proteins may have contributed to the evolution of CBASS cyclic nucleotide signaling.