6je9 | pdb_00006je9
Crystal structure of Nme1Cas9-sgRNA dimer mediated by double protein inhibitor AcrIIC3 monomers
Structural highlights
FunctionCAS9_NEIM8 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). In type II CRISPR systems correct processing of pre-crRNA requires a trans-encoded small RNA (tracrRNA), endogenous ribonuclease 3 (rnc) and this protein, although RNase 3 is not required for 5'-processing of crRNA in this strain. Cas9/crRNA/tracrRNA endonucleolytically cleaves linear or circular dsDNA target complementary to the spacer; Cas9 is inactive in the absence of the 2 guide RNAs (gRNA, PubMed:23940360). Cas9 recognizes the protospacer adjacent motif (PAM) in the CRISPR repeat sequences to help distinguish self versus nonself, as targets within the bacterial CRISPR locus do not have PAMs. PAM recognition is also required for catalytic activity. Plasmids containing sequences homologous to endogenous spacer elements and that have flanking PAM consensus sequences cannot transform this strain unless the cas9 gene is disrupted or critical residues of Cas9 are mutated.[1] [2] Publication Abstract from PubMedHigh-resolution Cas9 structures have yet to reveal catalytic conformations due to HNH nuclease domain positioning away from the cleavage site. Nme1Cas9 and Nme2Cas9 are compact nucleases for in vivo genome editing. Here, we report structures of meningococcal Cas9 homologs in complex with sgRNA, dsDNA, or the AcrIIC3 anti-CRISPR protein. DNA-bound structures represent an early step of target recognition, a later HNH pre-catalytic state, the HNH catalytic state, and a cleaved-target-DNA-bound state. In the HNH catalytic state of Nme1Cas9, the active site is seen poised at the scissile phosphodiester linkage of the target strand, providing a high-resolution view of the active conformation. The HNH active conformation activates the RuvC domain. Our structures explain how Nme1Cas9 and Nme2Cas9 read distinct PAM sequences and how AcrIIC3 inhibits Nme1Cas9 activity. These structures provide insights into Cas9 domain rearrangements, guide-target engagement, cleavage mechanism, and anti-CRISPR inhibition, facilitating the optimization of these genome-editing platforms. Structures of Neisseria meningitidis Cas9 Complexes in Catalytically Poised and Anti-CRISPR-Inhibited States.,Sun W, Yang J, Cheng Z, Amrani N, Liu C, Wang K, Ibraheim R, Edraki A, Huang X, Wang M, Wang J, Liu L, Sheng G, Yang Y, Lou J, Sontheimer EJ, Wang Y Mol Cell. 2019 Oct 22. pii: S1097-2765(19)30730-0. doi:, 10.1016/j.molcel.2019.09.025. PMID:31668930[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
| ||||||||||||||||||
