View source for 4f3e


==Crystal Structure of Thermus thermophilus HB8 CasA==
<StructureSection load='4f3e' size='340' side='right'caption='[[4f3e]], [[Resolution|resolution]] 2.40&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[4f3e]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Thermus_thermophilus_HB8 Thermus thermophilus HB8]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=4F3E OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=4F3E 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]] 2.4&#8491;</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=4f3e FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=4f3e OCA], [https://pdbe.org/4f3e PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=4f3e RCSB], [https://www.ebi.ac.uk/pdbsum/4f3e PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=4f3e ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/CSE1_THET8 CSE1_THET8] 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) (By similarity).  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 (By similarity).
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== Publication Abstract from PubMed ==
Prokaryotes make use of small RNAs encoded by CRISPR (clustered regularly interspaced short palindromic repeat) loci to provide immunity against bacteriophage or plasmid invasion. In Escherichia coli, the CRISPR-associated Complex for Antiviral Defense (Cascade) utilizes these RNAs to target foreign DNA for destruction. CasA, the largest subunit of Cascade, is essential for its function. Here we report the crystal structure of Thermus thermophilus CasA. The structure is composed of two domains that are arranged in a chair-like conformation with a novel fold forming the larger N-terminal domain. Docking of the crystal structure into cryo-electron microscopy maps reveals two loops in CasA likely have important functions in DNA target binding. Finally, DNA binding experiments show CasA is essential for binding of Cascade to DNA target.

Crystal structure of the largest subunit of a bacterial RNA-guided immune complex and its role in DNA target binding.,Mulepati S, Orr A, Bailey S J Biol Chem. 2012 May 23. PMID:22621933<ref>PMID:22621933</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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<div class="pdbe-citations 4f3e" style="background-color:#fffaf0;"></div>

==See Also==
*[[Endonuclease 3D structures|Endonuclease 3D structures]]
== References ==
<references/>
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</StructureSection>
[[Category: Large Structures]]
[[Category: Thermus thermophilus HB8]]
[[Category: Bailey S]]
[[Category: Mulepati S]]