2brt: Difference between revisions
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[[Image:2brt.gif|left|200px]]<br /><applet load="2brt" size=" | [[Image:2brt.gif|left|200px]]<br /><applet load="2brt" size="350" color="white" frame="true" align="right" spinBox="true" | ||
caption="2brt, resolution 2.20Å" /> | caption="2brt, resolution 2.20Å" /> | ||
'''ANTHOCYANIDIN SYNTHASE FROM ARABIDOPSIS THALIANA COMPLEXED WITH NARINGENIN'''<br /> | '''ANTHOCYANIDIN SYNTHASE FROM ARABIDOPSIS THALIANA COMPLEXED WITH NARINGENIN'''<br /> | ||
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==About this Structure== | ==About this Structure== | ||
2BRT is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Arabidopsis_thaliana Arabidopsis thaliana] with FE2, AKG and NAR as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Leucocyanidin_oxygenase Leucocyanidin oxygenase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.14.11.19 1.14.11.19] Known structural/functional Site: <scene name='pdbsite=AC1:Nar Binding Site For Chain A'>AC1</scene>. Full crystallographic information is available from [http:// | 2BRT is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Arabidopsis_thaliana Arabidopsis thaliana] with <scene name='pdbligand=FE2:'>FE2</scene>, <scene name='pdbligand=AKG:'>AKG</scene> and <scene name='pdbligand=NAR:'>NAR</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Leucocyanidin_oxygenase Leucocyanidin oxygenase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.14.11.19 1.14.11.19] Known structural/functional Site: <scene name='pdbsite=AC1:Nar+Binding+Site+For+Chain+A'>AC1</scene>. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2BRT OCA]. | ||
==Reference== | ==Reference== | ||
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[[Category: vitamin c]] | [[Category: vitamin c]] | ||
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Revision as of 11:27, 3 February 2008
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ANTHOCYANIDIN SYNTHASE FROM ARABIDOPSIS THALIANA COMPLEXED WITH NARINGENIN
OverviewOverview
During the biosynthesis of the tricyclic flavonoid natural products in, plants, oxidative modifications to the central C-ring are catalysed by, Fe(ii) and 2-oxoglutarate dependent oxygenases. The reactions catalysed by, three of these enzymes; flavone synthase I, flavonol synthase and, anthocyanidin synthase (ANS), are formally desaturations. In comparison, flavanone 3beta-hydroxylase catalyses hydroxylation at the C-3 pro-R, position of 2S-naringenin. Incubation of ANS with the unnatural substrate, (+/-)-naringenin results in predominantly C-3 hydroxylation to give, cis-dihydrokaempferol as the major product; trans-dihydrokaempferol and, the desaturation product, apigenin are also observed. Labelling studies, have demonstrated that some of the formal desaturation reactions catalysed, by ANS proceed via initial C-3 hydroxylation followed by dehydration at, the active site. We describe analyses of the reaction of ANS with 2S- and, 2R-naringenin substrates, including the anaerobic crystal structure of an, ANS-Fe-2-oxoglutarate-naringenin complex. Together the results reveal that, for the 'natural' C-2 stereochemistry of 2S-naringenin, C-3 hydroxylation, predominates (>9 : 1) over desaturation, probably due to the, inaccessibility of the C-2 hydrogen to the iron centre. For the, 2R-naringenin substrate, desaturation is significantly increased relative, to C-3 hydroxylation (ca. 1 : 1); this is probably a result of both the, C-3 pro-S and C-2 hydrogen atoms being accessible to the reactive, oxidising intermediate in this substrate. In contrast to the, hydroxylation-elimination desaturation mechanism for some ANS substrates, the results imply that the ANS catalysed desaturation of 2R-naringenin to, form apigenin proceeds with a syn-arrangement of eliminated hydrogen atoms, and not via an oxygenated (gem-diol) flavonoid intermediate. Thus, by, utilising flavonoid substrates with different C-2 stereochemistries, the, balance between C-3 hydroxylation or C-2, C-3 desaturation mechanisms can, be altered.
About this StructureAbout this Structure
2BRT is a Single protein structure of sequence from Arabidopsis thaliana with , and as ligands. Active as Leucocyanidin oxygenase, with EC number 1.14.11.19 Known structural/functional Site: . Full crystallographic information is available from OCA.
ReferenceReference
Structural and mechanistic studies on anthocyanidin synthase catalysed oxidation of flavanone substrates: the effect of C-2 stereochemistry on product selectivity and mechanism., Welford RW, Clifton IJ, Turnbull JJ, Wilson SC, Schofield CJ, Org Biomol Chem. 2005 Sep 7;3(17):3117-26. Epub 2005 Aug 1. PMID:16106293
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