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==Crystal structure of human cytochrome P4503A4 bound to an inhibitor ritonavir==
<StructureSection load='3nxu' size='340' side='right'caption='[[3nxu]], [[Resolution|resolution]] 2.00&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[3nxu]] is a 2 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=3NXU OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=3NXU 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&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=DMS:DIMETHYL+SULFOXIDE'>DMS</scene>, <scene name='pdbligand=HEM:PROTOPORPHYRIN+IX+CONTAINING+FE'>HEM</scene>, <scene name='pdbligand=RIT:RITONAVIR'>RIT</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=3nxu FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=3nxu OCA], [https://pdbe.org/3nxu PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=3nxu RCSB], [https://www.ebi.ac.uk/pdbsum/3nxu PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=3nxu ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/CP3A4_HUMAN CP3A4_HUMAN] Cytochromes P450 are a group of heme-thiolate monooxygenases. In liver microsomes, this enzyme is involved in an NADPH-dependent electron transport pathway. It performs a variety of oxidation reactions (e.g. caffeine 8-oxidation, omeprazole sulphoxidation, midazolam 1'-hydroxylation and midazolam 4-hydroxylation) of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics. Acts as a 1,8-cineole 2-exo-monooxygenase. The enzyme also hydroxylates etoposide.<ref>PMID:11159812</ref> 
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== Publication Abstract from PubMed ==
Ritonavir is a HIV protease inhibitor routinely prescribed to HIV patients that also potently inactivates cytochrome P4503A4 (CYP3A4), the major human drug-metabolizing enzyme. By inhibiting CYP3A4, ritonavir increases plasma concentrations of other anti-HIV drugs oxidized by CYP3A4 thereby improving clinical efficacy. Despite the importance and wide use of ritonavir in anti-HIV therapy, the precise mechanism of CYP3A4 inhibition remains unclear. The available data are inconsistent and suggest that ritonavir acts as a mechanism-based, competitive or mixed competitive-noncompetitive CYP3A4 inactivator. To resolve this controversy and gain functional and structural insights into the mechanism of CYP3A4 inhibition, we investigated the ritonavir binding reaction by kinetic and equilibrium analysis, elucidated how the drug affects redox properties of the hemoprotein, and determined the 2.0 A X-ray structure of the CYP3A4-ritonavir complex. Our results show that ritonavir is a type II ligand that perfectly fits into the CYP3A4 active site cavity and irreversibly binds to the heme iron via the thiazole nitrogen, which decreases the redox potential of the protein and precludes its reduction with the redox partner, cytochrome P450 reductase.

Structure and mechanism of the complex between cytochrome P4503A4 and ritonavir.,Sevrioukova IF, Poulos TL Proc Natl Acad Sci U S A. 2010 Oct 11. PMID:20937904<ref>PMID:20937904</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 3nxu" style="background-color:#fffaf0;"></div>

==See Also==
*[[Cytochrome P450 3D structures|Cytochrome P450 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Poulos TL]]
[[Category: Sevrioukova IF]]