5wqe
From Proteopedia
Crystal structure of Alicyclobacillus acidoterrestris C2c1 in complex with single-guide RNA at 3.1 Angstrom resolution
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 type V-B CRISPR-Cas system dual-RNA-guided DNA endonuclease. Here, we report the crystal structure of Alicyclobacillus acidoterrestris C2c1 in complex with a chimeric single-molecule guide RNA (sgRNA). AacC2c1 exhibits a bi-lobed architecture consisting of a REC and NUC lobe. The sgRNA scaffold forms a tetra-helical structure, distinct from previous predictions. The crRNA is located in the central channel of C2c1, and the tracrRNA resides in an external surface groove. Although AacC2c1 lacks a PAM-interacting domain, our analysis revealed that the PAM duplex has a similar binding position found in Cpf1. Importantly, C2c1-sgRNA system is highly sensitive to single-nucleotide mismatches between guide RNA and target DNA. The resulting reduction in off-target cleavage renders C2c1 a valuable addition to the current arsenal of genome-editing tools. Together, our findings indicate that sgRNA assembly is achieved through a mechanism distinct from that reported previously for Cas9 or Cpf1 endonucleases. C2c1-sgRNA Complex Structure Reveals RNA-Guided DNA Cleavage Mechanism.,Liu L, Chen P, Wang M, Li X, Wang J, Yin M, Wang Y Mol Cell. 2017 Jan 19;65(2):310-322. doi: 10.1016/j.molcel.2016.11.040. Epub 2016, Dec 15. PMID:27989439[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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