6jhw | pdb_00006jhw
Structure of anti-CRISPR AcrIIC3 and NmeCas9 HNH
Structural highlights
Function[A0A0T7L299_NEIME] 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. 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; Cas9 is inactive in the absence of the 2 guide RNAs (gRNA). 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.[HAMAP-Rule:MF_01480] Publication Abstract from PubMedClustered regularly interspaced short palindromic repeats (CRISPR)-Cas systems constitute the adaptive immunity of bacteria and archaea, degrading nucleic acids of invading phages and plasmids. In response, phages employ anti-CRISPR (Acr) proteins as a counterdefense mechanism to neutralize the host immunity. AcrIIC3 directly inhibits target DNA cleavage of type II-C Cas9 of Neisseria meningitidis. Here, we show that AcrIIC3 interacts with the HNH nuclease domain of N. meningitidis Cas9 to inhibit its nuclease activity in an allosteric manner. The crystal structure of the AcrIIC3-HNH complex reveals that AcrIIC3 binds opposite the active site on the HNH nuclease domain. AcrIIC3 employs a unique interface for HNH, allowing it to discriminate between Cas9 orthologs, which contrasts with the broad spectrum of Cas9 inhibition by AcrIIC1. Interface residues of HNH provide key electrostatic and hydrophobic interactions that determine the host specificity of AcrIIC3. Mutations that replace HNH interfaces of N. meningitidis Cas9 with those of Geobacillus stearothermophilus Cas9 or Campylobacter jejuni Cas9 significantly attenuate AcrIIC3 binding, illustrating that the divergent interaction surface confers the host specificity of AcrIIC3. Our study demonstrates that the variable sequences of binding interface can define the target specificity of Acr proteins, suggesting potential applications in Cas9 control for gene editing. Anti-CRISPR AcrIIC3 discriminates between Cas9 orthologs via targeting the variable surface of the HNH nuclease domain.,Kim Y, Lee SJ, Yoon HJ, Kim NK, Lee BJ, Suh JY FEBS J. 2019 Aug 7. doi: 10.1111/febs.15037. PMID:31389128[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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