7yhl
Crystal Structure of the ring nuclease Sso2081 from Saccharolobus solfataricus in complex with free phosphate
Structural highlights
FunctionRN081_SACS2 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). A nuclease that degrades cyclic oligoadenylates (cOA), second messengers that induce an antiviral state important for defense against invading nucleic acids. Destruction of cOA deactivates the Csx1 ribonuclease, preventing uncontrolled degradation of cellular RNA. Degrades cA4 (a tetraadenylate ring) into a linear diadenylate product with 5'-OH and 2',3'-cyclic phosphate termini. Is 10-fold more active than SSO1393, suggesting this is the major cA4 degradation enzyme. Is highly specific for cA4; it has very poor activity on cA6 and no discernible activity against a number of cyclic dinucletides. There may be 2 active sites per homodimer (PubMed:30232454).[1] Publication Abstract from PubMedThe cyclic oligoadenylates (cOAs) act as second messengers of the type III CRISPR immunity system through activating the auxiliary nucleases for indiscriminate RNA degradation. The cOA-degrading nucleases (ring nucleases) provide an 'off-switch' regulation of the signaling, thereby preventing cell dormancy or cell death. Here, we describe the crystal structures of the founding member of CRISPR-associated ring nuclease 1 (Crn1) Sso2081 from Saccharolobus solfataricus, alone, bound to phosphate ions or cA4 in both pre-cleavage and cleavage intermediate states. These structures together with biochemical characterizations establish the molecular basis of cA4 recognition and catalysis by Sso2081. The conformational changes in the C-terminal helical insert upon the binding of phosphate ions or cA4 reveal a gate-locking mechanism for ligand binding. The critical residues and motifs identified in this study provide a new insight to distinguish between cOA-degrading and -nondegrading CARF domain-containing proteins. Molecular basis of stepwise cyclic tetra-adenylate cleavage by the type III CRISPR ring nuclease Crn1/Sso2081.,Du L, Zhang D, Luo Z, Lin Z Nucleic Acids Res. 2023 Mar 21;51(5):2485-2495. doi: 10.1093/nar/gkad101. PMID:36807980[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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