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==Structural insights into the exosite-mediated activation of Factor IX by Factor XIa using cryoEM==
<StructureSection load='9ztk' size='340' side='right'caption='[[9ztk]], [[Resolution|resolution]] 3.70&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[9ztk]] is a 3 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=9ZTK OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=9ZTK 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]] 3.7&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=CA:CALCIUM+ION'>CA</scene>, <scene name='pdbligand=CGU:GAMMA-CARBOXY-GLUTAMIC+ACID'>CGU</scene>, <scene name='pdbligand=NAG:N-ACETYL-D-GLUCOSAMINE'>NAG</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=9ztk FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=9ztk OCA], [https://pdbe.org/9ztk PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=9ztk RCSB], [https://www.ebi.ac.uk/pdbsum/9ztk PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=9ztk ProSAT]</span></td></tr>
</table>
== Disease ==
[https://www.uniprot.org/uniprot/FA11_HUMAN FA11_HUMAN] Defects in F11 are the cause of factor XI deficiency (FA11D) [MIM:[https://omim.org/entry/612416 612416]; also known as plasma thromboplastin antecedent deficiency or Rosenthal syndrome. It is a hemorrhagic disease characterized by reduced levels and activity of factor XI resulting in moderate bleeding symptoms, usually occurring after trauma or surgery. Patients usually do not present spontaneous bleeding but women can present with menorrhagia. Hemorrhages are usually moderate.<ref>PMID:2813350</ref> <ref>PMID:1547342</ref> <ref>PMID:7888672</ref> <ref>PMID:7669672</ref> <ref>PMID:9401068</ref> <ref>PMID:9787168</ref> <ref>PMID:10027710</ref> <ref>PMID:10606881</ref> <ref>PMID:11895778</ref> <ref>PMID:15026311</ref> <ref>PMID:15180874</ref> <ref>PMID:15953011</ref> <ref>PMID:16607084</ref> <ref>PMID:18005151</ref> <ref>PMID:21668437</ref> <ref>PMID:21457405</ref> <ref>PMID:22016685</ref> <ref>PMID:22322133</ref> <ref>PMID:21999818</ref> <ref>PMID:22159456</ref> 
== Function ==
[https://www.uniprot.org/uniprot/FA11_HUMAN FA11_HUMAN] Factor XI triggers the middle phase of the intrinsic pathway of blood coagulation by activating factor IX.
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
BACKGROUND: Factor XI (FXI) occupies a unique and clinically significant niche, bridging the tissue factor-driven and contact-driven coagulation pathways. Irrespective of the trigger, activated factor XI (FXIa) contributes to clotting by activating factor IX (FIX). Biochemical studies established that this reaction requires the membrane-binding FIX-Gla domain to engage an exosite on the FXIa Apple 3 (A3) domain, that only become available upon FXI activation. Structural data for FXIa, FIX, FIXabeta, and the FXIa:FIX complex are lacking; current understanding relies on zymogen FXI crystal structures and homology modeling of FXIa after kallikrein. OBJECTIVES: Elucidate the high-resolution structure of FXIa in functionally relevant conformation in complex with FIX. METHODS: We utilized cryogenic electron microscopy (cryo-EM) to determine the structures of human FXIa in complex with its full-length substrate, FIX, and activated product, FIXabeta. RESULTS: We report the first cryo-EM structures of FXIa in complex with its substrate, FIX, and activated FIX (FIXabeta). The structures capture a functionally relevant conformational change in the FXIa catalytic domain and reveals the first view of the entire FIX and FIXabeta. Critically, we visualize the FIX-Gla domain precisely docked to the FXIa-A3 exosite on both subunits of the FXIa dimer. We also define the first step of proteolysis, visualizing the FIX Arg145 inserted into the primary specificity pocket of FXIa. CONCLUSIONS: The structures define the full FXIa:FIX interface providing a structural template for understanding the sequential activation of FIX and for developing a new class of selective allosteric antithrombotic agents.

Structural insights into the exosite-mediated activation of Factor IX by Factor XIa using cryo-EM.,Mohammed BM, Deavila S, Friet T, Dattilio I J Thromb Haemost. 2026 Aug 21:S1538-7836(26)00539-8. doi: , 10.1016/j.jtha.2026.08.015. PMID:42628751<ref>PMID:42628751</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 9ztk" style="background-color:#fffaf0;"></div>
== References ==
<references/>
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</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Mohammed BM]]