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==Cryo-EM structure of Triple ACE2-bound SARS-CoV-2 Trimer Spike at pH 5.5==
<StructureSection load='7kni' size='340' side='right'caption='[[7kni]], [[Resolution|resolution]] 3.91&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[7kni]] is a 6 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens] and [https://en.wikipedia.org/wiki/Severe_acute_respiratory_syndrome_coronavirus_2 Severe acute respiratory syndrome coronavirus 2]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=7KNI OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=7KNI 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]] 3.91&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><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=7kni FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=7kni OCA], [https://pdbe.org/7kni PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=7kni RCSB], [https://www.ebi.ac.uk/pdbsum/7kni PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=7kni ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/ACE2_HUMAN ACE2_HUMAN] Carboxypeptidase which converts angiotensin I to angiotensin 1-9, a peptide of unknown function, and angiotensin II to angiotensin 1-7, a vasodilator. Also able to hydrolyze apelin-13 and dynorphin-13 with high efficiency. May be an important regulator of heart function. In case of human coronaviruses SARS and HCoV-NL63 infections, serve as functional receptor for the spike glycoprotein of both coronaviruses.<ref>PMID:10969042</ref> <ref>PMID:10924499</ref> <ref>PMID:14647384</ref> 
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
The SARS-CoV-2 spike employs mobile receptor-binding domains (RBDs) to engage the human ACE2 receptor and to facilitate virus entry, which can occur through low-pH-endosomal pathways. To understand how ACE2 binding and low pH affect spike conformation, we determined cryo-electron microscopy structures-at serological and endosomal pH-delineating spike recognition of up to three ACE2 molecules. RBDs freely adopted "up" conformations required for ACE2 interaction, primarily through RBD movement combined with smaller alterations in neighboring domains. In the absence of ACE2, single-RBD-up conformations dominated at pH 5.5, resolving into a solitary all-down conformation at lower pH. Notably, a pH-dependent refolding region (residues 824-858) at the spike-interdomain interface displayed dramatic structural rearrangements and mediated RBD positioning through coordinated movements of the entire trimer apex. These structures provide a foundation for understanding prefusion-spike mechanics governing endosomal entry; we suggest that the low pH all-down conformation potentially facilitates immune evasion from RBD-up binding antibody.

Cryo-EM Structures of SARS-CoV-2 Spike without and with ACE2 Reveal a pH-Dependent Switch to Mediate Endosomal Positioning of Receptor-Binding Domains.,Zhou T, Tsybovsky Y, Gorman J, Rapp M, Cerutti G, Chuang GY, Katsamba PS, Sampson JM, Schon A, Bimela J, Boyington JC, Nazzari A, Olia AS, Shi W, Sastry M, Stephens T, Stuckey J, Teng IT, Wang P, Wang S, Zhang B, Friesner RA, Ho DD, Mascola JR, Shapiro L, Kwong PD Cell Host Microbe. 2020 Dec 9;28(6):867-879.e5. doi: 10.1016/j.chom.2020.11.004. , Epub 2020 Nov 17. PMID:33271067<ref>PMID:33271067</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 7kni" style="background-color:#fffaf0;"></div>

==See Also==
*[[Angiotensin-Converting Enzyme 3D structures|Angiotensin-Converting Enzyme 3D structures]]
== References ==
<references/>
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</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Severe acute respiratory syndrome coronavirus 2]]
[[Category: Gorman J]]
[[Category: Kwong PD]]
[[Category: Rapp M]]
[[Category: Shapiro L]]