View source for 5xvo


==E. fae Cas1-Cas2/prespacer/target ternary complex revealing DNA sampling and half-integration states==
<StructureSection load='5xvo' size='340' side='right'caption='[[5xvo]], [[Resolution|resolution]] 3.10&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[5xvo]] is a 18 chain structure with sequence from [https://en.wikipedia.org/wiki/Enterococcus_faecalis_TX0027 Enterococcus faecalis TX0027]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=5XVO OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=5XVO 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]] 3.1&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=MG:MAGNESIUM+ION'>MG</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=5xvo FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=5xvo OCA], [https://pdbe.org/5xvo PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=5xvo RCSB], [https://www.ebi.ac.uk/pdbsum/5xvo PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=5xvo ProSAT]</span></td></tr>
</table>
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== Publication Abstract from PubMed ==
CRISPR (clustered regularly interspaced short palindromic repeats) and the nearby cas (CRISPR-associated) operon establish an RNA-based adaptive immunity system in prokaryotes1-5. Molecular memory is created when a short foreign DNA-derived prespacer is integrated into the CRISPR array as a new spacer6-9. Whereas the RNA-guided CRISPR interference mechanism varies widely among CRISPR-Cas systems, the spacer integration mechanism is essentially identical7-9. The conserved Cas1 and Cas2 proteins form an integrase complex consisting two distal Cas1 dimers bridged by a Cas2 dimer in the middle6,10. The prespacer is bound by Cas1-Cas2 as a dual forked DNA, and the terminal 3'-OH of each 3'-overhang serves as an attacking nucleophile during integration11-14. Importantly, the prespacer is preferentially integrated into the leader-proximal region of the CRISPR array1,7,10,15, guided by the leader sequence and a pair of inverted repeats (IRs) inside the CRISPR repeat7,15-20. Spacer integration in the most well-studied Escherichia coli Type I-E CRISPR system further relies on the bacterial Integration Host Factor (IHF)21,22. In Type II-A CRISPR, however, Cas1-Cas2 alone integrates spacer efficiently in vitro18; other Cas proteins (Cas9 and Csn2) play accessory roles in prespacer biogenesis17,23. Focusing on the Enterococcus faecalis Type II-A system24, here we report four structure snapshots of Cas1-Cas2 during spacer integration. EfaCas1-Cas2 selectively binds to a splayed 30-bp prespacer bearing 4-nt 3'-overhangs. Three molecular events take place upon encountering a target: Cas1-Cas2/prespacer first searches for half-sites stochastically, then preferentially interacts with the leader-side CRISPR repeat and catalyzes a nucleophilic attack that connects one strand of the leader-proximal repeat to the prespacer 3'-overhang. Recognition of the spacer half-site requires DNA bending and leads to full integration. We derive a mechanistic framework explaining the stepwise spacer integration process and the leader-proximal preference.

How type II CRISPR-Cas establish immunity through Cas1-Cas2-mediated spacer integration.,Xiao Y, Ng S, Nam KH, Ke A Nature. 2017 Sep 4. doi: 10.1038/nature24020. PMID:28869593<ref>PMID:28869593</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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==See Also==
*[[Endonuclease 3D structures|Endonuclease 3D structures]]
== References ==
<references/>
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</StructureSection>
[[Category: Enterococcus faecalis TX0027]]
[[Category: Large Structures]]
[[Category: Ke A]]
[[Category: Nam KH]]
[[Category: Ng S]]
[[Category: Xiao Y]]