5u33
From Proteopedia
Crystal structure of AacC2c1-sgRNA-extended non-target DNA ternary complex
Structural highlights
Function[C2C1_ALIAG] 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). In type II CRISPR systems correct processing of pre-crRNA requires a trans-encoded small RNA (tracrRNA), endogenous ribonuclease 3 (rnc) and this protein (By similarity). The tracrRNA serves as a guide for ribonuclease 3-aided processing of pre-crRNA (By similarity). C2c1-crRNA-tracrRNA endonucleolytically cleaves dsDNA target complementary to the spacer; C2c1 is inactive in the absence of crRNA homologous to the target and tracrRNA (PubMed:26593719). C2c1 recognizes a short motif in the CRISPR repeat sequences (the 5' PAM or protospacer adjacent motif) to help distinguish self versus nonself, as targets within the bacterial CRISPR locus do not have PAMs (PubMed:26593719). PAM recognition is also required for catalytic activity. Cuts target DNA when C2c1, crRNA and tracrRNA are mixed (PubMed:26593719).[UniProtKB:A0Q5Y3][1] Publication Abstract from PubMedC2c1 is a newly identified guide RNA-mediated type V-B CRISPR-Cas endonuclease that site-specifically targets and cleaves both strands of target DNA. We have determined crystal structures of Alicyclobacillus acidoterrestris C2c1 (AacC2c1) bound to sgRNA as a binary complex and to target DNAs as ternary complexes, thereby capturing catalytically competent conformations of AacC2c1 with both target and non-target DNA strands independently positioned within a single RuvC catalytic pocket. Moreover, C2c1-mediated cleavage results in a staggered seven-nucleotide break of target DNA. crRNA adopts a pre-ordered five-nucleotide A-form seed sequence in the binary complex, with release of an inserted tryptophan, facilitating zippering up of 20-bp guide RNA:target DNA heteroduplex on ternary complex formation. Notably, the PAM-interacting cleft adopts a "locked" conformation on ternary complex formation. Structural comparison of C2c1 ternary complexes with their Cas9 and Cpf1 counterparts highlights the diverse mechanisms adopted by these distinct CRISPR-Cas systems, thereby broadening and enhancing their applicability as genome editing tools. PAM-Dependent Target DNA Recognition and Cleavage by C2c1 CRISPR-Cas Endonuclease.,Yang H, Gao P, Rajashankar KR, Patel DJ Cell. 2016 Dec 15;167(7):1814-1828.e12. doi: 10.1016/j.cell.2016.11.053. PMID:27984729[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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