4wnz
From Proteopedia
Crystal structure of Pyrococcus furiosus Cmr4 (Cas7)
Structural highlights
Function[CMR4_PYRFU] 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 sequences complementary to antecedent mobile elements and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA), formerly called psiRNA (prokaryotic silencing) in this organism. Part of the Cmr ribonucleoprotein complex which has divalent cation-dependent endoribonuclease activity specific for ssRNA complementary to the crRNA, generating 5' hydroxy- and 3' phosphate or 2'-3' cyclic phosphate termini. It is not known which subunit has endoribonuclease activity. Cmr complex does not cleave ssDNA complementary to the crRNA. Cleavage of invading RNA is guided by the crRNA; substrate cleavage occurs a fixed distance (14 nt) from the 3' end of the crRNA. In vitro reconstitution shows Cmr1-2 and Cmr5 are not necessary for cleavage.[1] Publication Abstract from PubMedClustered regularly interspaced short palindromic repeat (CRISPR) loci and CRISPR-associated (Cas) proteins form an adaptive immune system that protects prokaryotes against plasmids and viruses. The Cmr complex, a type III-B effector complex, uses the CRISPR RNA (crRNA) as a guide to target RNA. Here, we show that the Cmr complex of Pyrococcus furiosus cleaves RNA at multiple sites that are 6 nt apart and are positioned relative to the 5'-end of the crRNA. We identified Cmr4 as the slicer and determined its crystal structure at 2.8 A resolution. In the crystal, Cmr4 forms a helical filament that most likely reflects its structural organization in the Cmr complex. The putative active site is located at the inner surface of the filament where the guide and substrate RNA are thought to bind. The filament structure of Cmr4 accounts for multiple periodic cleavage sites on the substrate. Our study provides new insights into the structure and mechanism of the RNA-targeting Cmr complex. Cmr4 is the slicer in the RNA-targeting Cmr CRISPR complex.,Zhu X, Ye K Nucleic Acids Res. 2014 Dec 24. pii: gku1355. PMID:25541196[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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Categories: Large Structures | Pyrfu | Ye, K | Zhu, X | Cmr cmplex | Crispr-cas system | Hydrolase | Nuclease | Ramp domain
