6o0y
From Proteopedia
Conformational states of Cas9-sgRNA-DNA ternary complex in the presence of magnesium
Structural highlights
Function[CAS9_STRP1] 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). In type II CRISPR systems correct processing of pre-crRNA requires a trans-encoded small RNA (tracrRNA), endogenous ribonuclease 3 (rnc) and this protein. The tracrRNA serves as a guide for ribonuclease 3-aided processing of pre-crRNA. Subsequently Cas9/crRNA/tracrRNA endonucleolytically cleaves linear or circular dsDNA target complementary to the spacer. The target strand not complementary to crRNA is first cut endonucleolytically, then trimmed by 3'-5' exonucleolytically. DNA-binding requires protein and both RNA species. Cas9 probably recognizes a short motif in the CRISPR repeat sequences (the PAM or protospacer adjacent motif) to help distinguish self versus nonself.[1] [2] Publication Abstract from PubMedThe RNA-guided Cas9 endonuclease from Streptococcus pyogenes is a single-turnover enzyme that displays a stable product state after double-stranded-DNA cleavage. Here, we present cryo-EM structures of precatalytic, postcatalytic and product states of the active Cas9-sgRNA-DNA complex in the presence of Mg(2+). In the precatalytic state, Cas9 adopts the 'checkpoint' conformation with the HNH nuclease domain positioned far away from the DNA. Transition to the postcatalytic state involves a dramatic ~34-A swing of the HNH domain and disorder of the REC2 recognition domain. The postcatalytic state captures the cleaved substrate bound to the catalytically competent HNH active site. In the product state, the HNH domain is disordered, REC2 returns to the precatalytic conformation, and additional interactions of REC3 and RuvC with nucleic acids are formed. The coupled domain motions and interactions between the enzyme and the RNA-DNA hybrid provide new insights into the mechanism of genome editing by Cas9. Cryo-EM structures reveal coordinated domain motions that govern DNA cleavage by Cas9.,Zhu X, Clarke R, Puppala AK, Chittori S, Merk A, Merrill BJ, Simonovic M, Subramaniam S Nat Struct Mol Biol. 2019 Jul 8. pii: 10.1038/s41594-019-0258-2. doi:, 10.1038/s41594-019-0258-2. PMID:31285607[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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