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==Crystal structure of a CRISPR RNA-guided surveillance complex, Cascade, bound to a ssDNA target==
<StructureSection load='4qyz' size='340' side='right'caption='[[4qyz]], [[Resolution|resolution]] 3.03&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[4qyz]] is a 13 chain structure with sequence from [https://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli], [https://en.wikipedia.org/wiki/Escherichia_coli_K-12 Escherichia coli K-12] and [https://en.wikipedia.org/wiki/Escherichia_virus_Lambda Escherichia virus Lambda]. The January 2015 RCSB PDB [https://pdb.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/index.html Molecule of the Month] feature on ''Cascade and CRISPR''  by David Goodsell is [https://dx.doi.org/10.2210/rcsb_pdb/mom_2015_1 10.2210/rcsb_pdb/mom_2015_1]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=4QYZ OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=4QYZ FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 3.0303&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=ZN:ZINC+ION'>ZN</scene></td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=4qyz FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=4qyz OCA], [https://pdbe.org/4qyz PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=4qyz RCSB], [https://www.ebi.ac.uk/pdbsum/4qyz PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=4qyz ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/CSE1_ECOLI CSE1_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).<ref>PMID:21255106</ref> <ref>PMID:21460843</ref> <ref>PMID:22621933</ref> <ref>PMID:22521690</ref>   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, probably via interactions with CasA, nicks target DNA and then unwinds and cleaves the target, leading to DNA degradation and invader neutralization. CasA is not required for formation of Cascade, but probably enhances binding to and subsequent recognition of both target dsDNA and ssDNA.<ref>PMID:21255106</ref> <ref>PMID:21460843</ref> <ref>PMID:22621933</ref> <ref>PMID:22521690</ref> 
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
In prokaryotes, RNA derived from type I and type III CRISPR loci direct large ribonucleoprotein complexes to destroy invading bacteriophage and plasmids. In Escherichia coli, this 405-kDa complex is called Cascade. Here, we report the 3.03A crystal structure of Cascade bound to a single-stranded DNA target. The structure reveals that the CRISPR RNA and target strands do not form a double helix but instead adopt an underwound ribbon-like structure. This non-canonical structure is facilitated by rotation of every sixth nucleotide out of the RNA-DNA hybrid and is stabilized by the highly interlocked organization of protein subunits. These studies provide insight into both the assembly and the activity of this complex and suggest a mechanism to enforce fidelity of target binding.

Crystal structure of a CRISPR RNA-guided surveillance complex bound to a ssDNA target.,Mulepati S, Heroux A, Bailey S Science. 2014 Aug 14. pii: 1256996. PMID:25123481<ref>PMID:25123481</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 4qyz" style="background-color:#fffaf0;"></div>

==See Also==
*[[CRISPR type I-E (Cascade)|CRISPR type I-E (Cascade)]]
*[[CRISPR-Cas|CRISPR-Cas]]
*[[CRISPR-Cas Part II|CRISPR-Cas Part II]]
*[[Endonuclease 3D structures|Endonuclease 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Cascade and CRISPR]]
[[Category: Escherichia coli]]
[[Category: Escherichia coli K-12]]
[[Category: Escherichia virus Lambda]]
[[Category: Large Structures]]
[[Category: RCSB PDB Molecule of the Month]]
[[Category: Bailey S]]
[[Category: Mulepati S]]