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| | {{STRUCTURE_2j2f| PDB=2j2f | SCENE= }} | | {{STRUCTURE_2j2f| PDB=2j2f | SCENE= }} |
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| - | '''THE T199D MUTANT OF STEAROYL ACYL CARRIER PROTEIN DESATURASE FROM RICINUS COMMUNIS (CASTOR BEAN)'''
| + | ===THE T199D MUTANT OF STEAROYL ACYL CARRIER PROTEIN DESATURASE FROM RICINUS COMMUNIS (CASTOR BEAN)=== |
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| - | ==Overview==
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| - | Sequence analysis of the diiron cluster-containing soluble desaturases suggests they are unrelated to other diiron enzymes; however, structural alignment of the core four-helix bundle of desaturases to other diiron enzymes reveals a conserved iron binding motif with similar spacing in all enzymes of this structural class, implying a common evolutionary ancestry. Detailed structural comparison of the castor desaturase with that of a peroxidase, rubrerythrin, shows remarkable conservation of both identity and geometry of residues surrounding the diiron center, with the exception of residue 199. Position 199 is occupied by a threonine in the castor desaturase, but the equivalent position in rubrerythrin contains a glutamic acid. We previously hypothesized that a carboxylate in this location facilitates oxidase chemistry in rubrerythrin by the close apposition of a residue capable of facilitating proton transfer to the activated oxygen (in a hydrophobic cavity adjacent to the diiron center based on the crystal structure of the oxygen-binding mimic azide). Here we report that desaturase mutant T199D binds substrate but its desaturase activity decreases by approximately 2 x 10(3)-fold. However, it shows a >31-fold increase in peroxide-dependent oxidase activity with respect to WT desaturase, as monitored by single-turnover stopped-flow spectrometry. A 2.65-A crystal structure of T199D reveals active-site geometry remarkably similar to that of rubrerythrin, consistent with its enhanced function as an oxidase enzyme. That a single amino acid substitution can switch reactivity from desaturation to oxidation provides experimental support for the hypothesis that the desaturase evolved from an ancestral oxidase enzyme.
| + | The line below this paragraph, {{ABSTRACT_PUBMED_17088542}}, adds the Publication Abstract to the page |
| | + | (as it appears on PubMed at http://www.pubmed.gov), where 17088542 is the PubMed ID number. |
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| | + | {{ABSTRACT_PUBMED_17088542}} |
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| | ==About this Structure== | | ==About this Structure== |
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| | [[Category: Plastid]] | | [[Category: Plastid]] |
| | [[Category: Transit peptide]] | | [[Category: Transit peptide]] |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 08:15:02 2008'' | + | |
| | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 17:34:47 2008'' |
Revision as of 14:34, 28 July 2008
Template:STRUCTURE 2j2f
THE T199D MUTANT OF STEAROYL ACYL CARRIER PROTEIN DESATURASE FROM RICINUS COMMUNIS (CASTOR BEAN)
Template:ABSTRACT PUBMED 17088542
About this Structure
2J2F is a Single protein structure of sequence from Ricinus communis. Full crystallographic information is available from OCA.
Reference
A single mutation in the castor Delta9-18:0-desaturase changes reaction partitioning from desaturation to oxidase chemistry., Guy JE, Abreu IA, Moche M, Lindqvist Y, Whittle E, Shanklin J, Proc Natl Acad Sci U S A. 2006 Nov 14;103(46):17220-4. Epub 2006 Nov 6. PMID:17088542
Page seeded by OCA on Mon Jul 28 17:34:47 2008
