4tvx
From Proteopedia
Crystal structure of the E. coli CRISPR RNA-guided surveillance complex, Cascade
Structural highlights
FunctionCSE2_ECOLI 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).[1] [2] A component of Cascade, which participates in CRISPR interference, the third stage of CRISPR immunity. Cascade binds both crRNA and in a sequence-specific manner negatively supercoiled dsDNA target. This leads to the formation of an R-loop in which the crRNA binds the target DNA, displacing the noncomplementary strand. Cas3 is recruited to Cascade, nicks target DNA and then unwinds and cleaves the target, leading to DNA degradation and invader neutralization.[3] [4] Publication Abstract from PubMedClustered regularly interspaced short palindromic repeats (CRISPRs) are essential components of RNA-guided adaptive immune systems that protect bacteria and archaea from viruses and plasmids. In Escherichia coli, short CRISPR-derived RNAs (crRNAs) assemble into a 405 kDa multi-subunit surveillance complex called Cascade (CRISPR-associated complex for antiviral defense). Here, we present the 3.24 A resolution x-ray crystal structure of Cascade. Eleven proteins and a 61-nucleotide crRNA assemble into a sea-horse-shaped architecture that binds double-stranded DNA targets complementary to the crRNA-guide sequence. Conserved sequences on the 3'- and 5'-ends of the crRNA are anchored by proteins at opposite ends of the complex, while the guide sequence is displayed along a helical assembly of six interwoven subunits that present 5-nucleotide segments of the crRNA in pseudo A-form configuration. The structure of Cascade suggests a mechanism for assembly and provides insights into the mechanisms of target recognition. Crystal structure of the CRISPR RNA-guided surveillance complex from Escherichia coli.,Jackson RN, Golden SM, van Erp PB, Carter J, Westra ER, Brouns SJ, van der Oost J, Terwilliger TC, Read RJ, Wiedenheft B Science. 2014 Aug 7. pii: 1256328. PMID:25103409[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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