1d6h

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{{STRUCTURE_1d6h| PDB=1d6h | SCENE= }}
{{STRUCTURE_1d6h| PDB=1d6h | SCENE= }}
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'''CHALONE SYNTHASE (N336A MUTANT COMPLEXED WITH COA)'''
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===CHALONE SYNTHASE (N336A MUTANT COMPLEXED WITH COA)===
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==Overview==
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Chalcone synthase (CHS) catalyzes formation of the phenylpropanoid chalcone from one p-coumaroyl-CoA and three malonyl-coenzyme A (CoA) thioesters. The three-dimensional structure of CHS [Ferrer, J.-L., Jez, J. M., Bowman, M. E., Dixon, R. A., and Noel, J. P. (1999) Nat. Struct. Biol. 6, 775-784] suggests that four residues (Cys164, Phe215, His303, and Asn336) participate in the multiple decarboxylation and condensation reactions catalyzed by this enzyme. Here, we functionally characterize 16 point mutants of these residues for chalcone production, malonyl-CoA decarboxylation, and the ability to bind CoA and acetyl-CoA. Our results confirm Cys164's role as the active-site nucleophile in polyketide formation and elucidate the importance of His303 and Asn336 in the malonyl-CoA decarboxylation reaction. We suggest that Phe215 may help orient substrates at the active site during elongation of the polyketide intermediate. To better understand the structure-function relationships in some of these mutants, we also determined the crystal structures of the CHS C164A, H303Q, and N336A mutants refined to 1.69, 2.0, and 2.15 A resolution, respectively. The structure of the C164A mutant reveals that the proposed oxyanion hole formed by His303 and Asn336 remains undisturbed, allowing this mutant to catalyze malonyl-CoA decarboxylation without chalcone formation. The structures of the H303Q and N336A mutants support the importance of His303 and Asn336 in polarizing the thioester carbonyl of malonyl-CoA during the decarboxylation reaction. In addition, both of these residues may also participate in stabilizing the tetrahedral transition state during polyketide elongation. Conservation of the catalytic functions of the active-site residues may occur across a wide variety of condensing enzymes, including other polyketide and fatty acid synthases.
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{{ABSTRACT_PUBMED_10653632}}
==About this Structure==
==About this Structure==
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[[Category: Polypetide synthase]]
[[Category: Polypetide synthase]]
[[Category: Site-directed mutant]]
[[Category: Site-directed mutant]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 13:30:20 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 22:32:12 2008''

Revision as of 19:32, 30 June 2008

Image:1d6h.png

Template:STRUCTURE 1d6h

CHALONE SYNTHASE (N336A MUTANT COMPLEXED WITH COA)

Template:ABSTRACT PUBMED 10653632

About this Structure

1D6H is a Single protein structure of sequence from Medicago sativa. Full crystallographic information is available from OCA.

Reference

Dissection of malonyl-coenzyme A decarboxylation from polyketide formation in the reaction mechanism of a plant polyketide synthase., Jez JM, Ferrer JL, Bowman ME, Dixon RA, Noel JP, Biochemistry. 2000 Feb 8;39(5):890-902. PMID:10653632

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