6tug
From Proteopedia
Enterococcus italicus Csm6 bound to cyclic hexa-2'-fluoro-hexa-dAMP
Structural highlights
Function[CSM6_ENTI1] CRISPR (clustered regularly interspaced short palindromic repeat) is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain spacers, sequences complementary to antecedent mobile elements, and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA) (Probable). The type III-A Csm effector complex binds crRNA and acts as a crRNA-guided RNase, DNase and cyclic oligoadenylate synthase; binding of target RNA cognate to the crRNA is required for all activities. In a heterologous host the appropriately targeted Csm effector complex prevents growth of dsDNA phage phiNM1-gamma6. This protein is not part of the Csm effector complex (PubMed:28722012).[1] A single-strand-specific endoribonuclease (ssRNase) (PubMed:28722012). Activity is stimulated by cyclic oligoadenylates (cOA); maximal stimulation is seen with cyclic hexaadenylate (cA6) (PubMed:28722012).[2] Publication Abstract from PubMedBacterial and archaeal CRISPR-Cas systems provide RNA-guided immunity against genetic invaders such as bacteriophages and plasmids. Upon target RNA recognition, type III CRISPR-Cas systems produce cyclic-oligoadenylate second messengers that activate downstream effectors, including Csm6 ribonucleases, via their CARF domains. Here, we show that Enteroccocus italicus Csm6 (EiCsm6) degrades its cognate cyclic hexa-AMP (cA6) activator, and report the crystal structure of EiCsm6 bound to a cA6 mimic. Our structural, biochemical, and in vivo functional assays reveal how cA6 recognition by the CARF domain activates the Csm6 HEPN domains for collateral RNA degradation, and how CARF domain-mediated cA6 cleavage provides an intrinsic off-switch to limit Csm6 activity in the absence of ring nucleases. These mechanisms facilitate rapid invader clearance and ensure termination of CRISPR interference to limit self-toxicity. Activation and self-inactivation mechanisms of the cyclic oligoadenylate-dependent CRISPR ribonuclease Csm6.,Garcia-Doval C, Schwede F, Berk C, Rostol JT, Niewoehner O, Tejero O, Hall J, Marraffini LA, Jinek M Nat Commun. 2020 Mar 27;11(1):1596. doi: 10.1038/s41467-020-15334-5. PMID:32221291[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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