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| {{STRUCTURE_2qw8| PDB=2qw8 | SCENE= }} | | {{STRUCTURE_2qw8| PDB=2qw8 | SCENE= }} |
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| '''Structure of Eugenol Synthase from Ocimum basilicum'''
| | ===Structure of Eugenol Synthase from Ocimum basilicum=== |
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| ==Overview==
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| Phenylpropenes, a large group of plant volatile compounds that serve in multiple roles in defense and pollinator attraction, contain a propenyl side chain. Eugenol synthase (EGS) catalyzes the reductive displacement of acetate from the propenyl side chain of the substrate coniferyl acetate to produce the allyl-phenylpropene eugenol. We report here the structure determination of EGS from basil (Ocimum basilicum) by protein x-ray crystallography. EGS is structurally related to the short-chain dehydrogenase/reductases (SDRs), and in particular, enzymes in the isoflavone-reductase-like subfamily. The structure of a ternary complex of EGS bound to the cofactor NADP(H) and a mixed competitive inhibitor EMDF ((7S,8S)-ethyl (7,8-methylene)-dihydroferulate) provides a detailed view of the binding interactions within the EGS active site and a starting point for mutagenic examination of the unusual reductive mechanism of EGS. The key interactions between EMDF and the EGS-holoenzyme include stacking of the phenyl ring of EMDF against the cofactor's nicotinamide ring and a water-mediated hydrogen-bonding interaction between the EMDF 4-hydroxy group and the side-chain amino moiety of a conserved lysine residue, Lys132. The C4 carbon of nicotinamide resides immediately adjacent to the site of hydride addition, the C7 carbon of cinnamyl acetate substrates. The inhibitor-bound EGS structure suggests a two-step reaction mechanism involving the formation of a quinone-methide prior to reduction. The formation of this intermediate is promoted by a hydrogen-bonding network that favors deprotonation of the substrate's 4-hydroxyl group and disfavors binding of the acetate moiety, akin to a push-pull catalytic mechanism. Notably, the catalytic involvement in EGS of the conserved Lys132 in preparing the phenolic substrate for quinone methide formation through the proton-relay network appears to be an adaptation of the analogous role in hydrogen bonding played by the equivalent lysine residue in other enzymes of the SDR family.
| | The line below this paragraph, {{ABSTRACT_PUBMED_17912370}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 17912370 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_17912370}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Plant protein]] | | [[Category: Plant protein]] |
| [[Category: Short-chain dehydrogenase/reductase]] | | [[Category: Short-chain dehydrogenase/reductase]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Wed Jun 11 10:44:14 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 16:54:02 2008'' |
