View source for 3cqn


==Crystal Structure of the Lipocalin domain of Violaxanthin de-epoxidase (VDE) at pH7==
<StructureSection load='3cqn' size='340' side='right'caption='[[3cqn]], [[Resolution|resolution]] 2.00&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[3cqn]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Arabidopsis_thaliana Arabidopsis thaliana]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=3CQN OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=3CQN 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='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=3cqn FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=3cqn OCA], [https://pdbe.org/3cqn PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=3cqn RCSB], [https://www.ebi.ac.uk/pdbsum/3cqn PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=3cqn ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/VDE_ARATH VDE_ARATH] Part of the xanthophyll (or violaxanthin) cycle for controlling the concentration of zeaxanthin in chloroplasts. Catalyzes the two-step mono de-epoxidation reaction. Stereospecific for all-trans xanthophylls. Zeaxanthin induces the dissipation of excitation energy in the chlorophyll of the light-harvesting protein complex of photosystem II.<ref>PMID:10982442</ref> <ref>PMID:11855651</ref> <ref>PMID:9668132</ref> 
== Evolutionary Conservation ==
[[Image:Consurf_key_small.gif|200px|right]]
Check<jmol>
  <jmolCheckbox>
    <scriptWhenChecked>; select protein; define ~consurf_to_do selected; consurf_initial_scene = true; script "/wiki/ConSurf/cq/3cqn_consurf.spt"</scriptWhenChecked>
    <scriptWhenUnchecked>script /wiki/extensions/Proteopedia/spt/initialview03.spt</scriptWhenUnchecked>
    <text>to colour the structure by Evolutionary Conservation</text>
  </jmolCheckbox>
</jmol>, as determined by [http://consurfdb.tau.ac.il/ ConSurfDB]. You may read the [[Conservation%2C_Evolutionary|explanation]] of the method and the full data available from [http://bental.tau.ac.il/new_ConSurfDB/main_output.php?pdb_ID=3cqn ConSurf].
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== Publication Abstract from PubMed ==
Plants adjust their photosynthetic activity to changing light conditions. A central regulation of photosynthesis depends on the xanthophyll cycle, in which the carotenoid violaxanthin is converted into zeaxanthin in strong light, thus activating the dissipation of the excess absorbed energy as heat and the scavenging of reactive oxygen species. Violaxanthin deepoxidase (VDE), the enzyme responsible for zeaxanthin synthesis, is activated by the acidification of the thylakoid lumen when photosynthetic electron transport exceeds the capacity of assimilatory reactions: at neutral pH, VDE is a soluble and inactive enzyme, whereas at acidic pH, it attaches to the thylakoid membrane where it binds its violaxanthin substrate. VDE also uses ascorbate as a cosubstrate with a pH-dependent Km that may reflect a preference for ascorbic acid. We determined the structures of the central lipocalin domain of VDE (VDEcd) at acidic and neutral pH. At neutral pH, VDEcd is monomeric with its active site occluded within a lipocalin barrel. Upon acidification, the barrel opens up and the enzyme appears as a dimer. A channel linking the two active sites of the dimer can harbor the entire carotenoid substrate and thus may permit the parallel deepoxidation of the two violaxanthin beta-ionone rings, making VDE an elegant example of the adaptation of an asymmetric enzyme to its symmetric substrate.

A structural basis for the pH-dependent xanthophyll cycle in Arabidopsis thaliana.,Arnoux P, Morosinotto T, Saga G, Bassi R, Pignol D Plant Cell. 2009 Jul;21(7):2036-44. Epub 2009 Jul 28. PMID:19638474<ref>PMID:19638474</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 3cqn" style="background-color:#fffaf0;"></div>
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Arabidopsis thaliana]]
[[Category: Large Structures]]
[[Category: Arnoux P]]
[[Category: Morosinotto T]]
[[Category: Pignol D]]