View source for 9zq6


==Structure of SpyCas9 in complex with the anti-CRISPR protein AcrIIA26==
<StructureSection load='9zq6' size='340' side='right'caption='[[9zq6]], [[Resolution|resolution]] 2.98&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[9zq6]] is a 3 chain structure with sequence from [https://en.wikipedia.org/wiki/Streptococcus Streptococcus] and [https://en.wikipedia.org/wiki/Streptococcus_pyogenes_M1_GAS Streptococcus pyogenes M1 GAS]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=9ZQ6 OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=9ZQ6 FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">Electron Microscopy, [[Resolution|Resolution]] 2.98&#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=9zq6 FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=9zq6 OCA], [https://pdbe.org/9zq6 PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=9zq6 RCSB], [https://www.ebi.ac.uk/pdbsum/9zq6 PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=9zq6 ProSAT]</span></td></tr>
</table>
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== Publication Abstract from PubMed ==
CRISPR-Cas9 systems provide adaptive immunity in prokaryotes by targeting and cleaving invading phage DNA. In response, phages have evolved anti-CRISPR (Acr) proteins to inhibit Cas9 and evade this immune response. AcrIIA26 is a type II-A anti-CRISPR protein that inhibits Streptococcus pyogenes Cas9 (SpyCas9) DNA binding, but its molecular mechanism remains unclear. Here, we determined the 3.0 A resolution cryo-EM structure of AcrIIA26 in complex with SpyCas9-single-guide RNA, revealing a dual inhibition mechanism. AcrIIA26 adopts a novel fold comprising a central beta-sheet flanked by two alpha-helical bundles. The 5-helix bundle, which features a negatively charged surface whose shape mimics duplex DNA, occupies the same position as the protospacer adjacent motif (PAM) duplex in target-bound Cas9. This directly blocks PAM recognition by burying critical residues R1333 and R1335 in the PAM-interacting domain. Mutagenesis confirmed that residues E49 and D50 in AcrIIA26 are essential for this interaction. Simultaneously, the 4-helix bundle binds the Cas9 REC lobe and sterically prevents the conformational changes required for Cas9 activation, with mutation of AcrIIA26 F121 completely eliminating inhibitory activity. Structural comparisons reveal that despite diverse folds, multiple anti-CRISPRs convergently evolved to block PAM recognition, highlighting this as a critical vulnerability in Cas9 function. Our findings provide mechanistic insights into AcrIIA26 inhibition and offer a foundation for engineering improved Cas9 off-switches for genome editing applications.

Structural basis for inhibition of SpyCas9 by the anti-CRISPR protein AcrIIA26.,Zheng I, Learn B, Bailey S Biochem J. 2026 Mar 4;483(3):289-300. doi: 10.1042/BCJ20250364. PMID:41553775<ref>PMID:41553775</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 9zq6" style="background-color:#fffaf0;"></div>
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Large Structures]]
[[Category: Streptococcus]]
[[Category: Streptococcus pyogenes M1 GAS]]
[[Category: Bailey S]]
[[Category: Learn B]]
[[Category: Zheng I]]