5mga
Structure of the Cpf1 endonuclease R-loop complex after DNA cleavage
Structural highlights
FunctionCS12A_FRATN 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). Has endonuclease activity on pre-crRNA and dsDNA, using different active sites. A single-RNA guided endonuclease that is also capable of guiding crRNA processing; correct processing of pre-crRNA requires only this protein and the CRISPR locus (PubMed:26422227, PubMed:27096362). pre-crRNA processing proceeds by an intramolecular nucleophilic attack on the scissile phosphate by the 2'-OH of the upstream ribonucleotide, the divalent cation (which is bound by the crRNA) is probably required for ordering the crRNA pseudoknot and/or increasing RNA binding (PubMed:28431230). RNA mutagenesis studies show pre-crRNA cleavage is highly sequence- and structure-specific (PubMed:27096362). Forms a complex with crRNA and complementary dsDNA, where the crRNA displaces the non-target DNA strand and directs endonucleolytic cleavage of both strands of the DNA (PubMed:26422227, PubMed:27096362, PubMed:28431230). Cleavage results in staggered 5-base 5' overhangs 14-18 and 21-23 bases downstream of the PAM (protospacer adjacent motif) on the non-target and target strands respectively (PubMed:26422227, PubMed:28431230, PubMed:28562584). Both target and non-target strand DNA are probably independently cleaved in the same active site (PubMed:28431230, PubMed:28562584). When this protein is expressed in E.coli it prevents plasmids homologous to the first CRISPR spacer from transforming, formally showing it is responsible for plasmid immunity (PubMed:26422227).[1] [2] [3] [4] Publication Abstract from PubMedCpf1 is an RNA-guided endonuclease that is emerging as a powerful genome-editing tool. Here we provide insight into its DNA-targeting mechanism by determining the structure of Francisella novicida Cpf1 with the triple-stranded R-loop generated after DNA cleavage. The structure reveals the machinery involved in DNA unwinding to form a CRISPR RNA (crRNA)-DNA hybrid and a displaced DNA strand. The protospacer adjacent motif (PAM) is recognized by the PAM-interacting domain. The loop-lysine helix-loop motif in this domain contains three conserved lysine residues that are inserted in a dentate manner into the double-stranded DNA. Unzipping of the double-stranded DNA occurs in a cleft arranged by acidic and hydrophobic residues facilitating the crRNA-DNA hybrid formation. The PAM single-stranded DNA is funnelled towards the nuclease site through a mixed hydrophobic and basic cavity. In this catalytic conformation, the PAM-interacting domain and the helix-loop-helix motif in the REC1 domain adopt a 'rail' shape and 'flap-on' conformations, respectively, channelling the PAM strand into the cavity. A steric barrier between the RuvC-II and REC1 domains forms the 'septum', separating the displaced PAM strand and the crRNA-DNA hybrid, avoiding DNA re-annealing. Mutations in key residues reveal a mechanism linking the PAM and DNA nuclease sites. Analysis of the Cpf1 structures proposes a singular working model of RNA-guided DNA cleavage, suggesting new avenues for redesign of Cpf1. Structure of the Cpf1 endonuclease R-loop complex after target DNA cleavage.,Stella S, Alcon P, Montoya G Nature. 2017 Jun 22;546(7659):559-563. doi: 10.1038/nature22398. Epub 2017 May, 31. PMID:28562584[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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