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1zg3

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[[Image:1zg3.gif|left|200px]]
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{{STRUCTURE_1zg3| PDB=1zg3 | SCENE= }}
{{STRUCTURE_1zg3| PDB=1zg3 | SCENE= }}
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'''Crystal structure of the isoflavanone 4'-O-methyltransferase complexed with SAH and 2,7,4'-trihydroxyisoflavanone'''
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===Crystal structure of the isoflavanone 4'-O-methyltransferase complexed with SAH and 2,7,4'-trihydroxyisoflavanone===
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==Overview==
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In leguminous plants such as pea (Pisum sativum), alfalfa (Medicago sativa), barrel medic (Medicago truncatula), and chickpea (Cicer arietinum), 4'-O-methylation of isoflavonoid natural products occurs early in the biosynthesis of defense chemicals known as phytoalexins. However, among these four species, only pea catalyzes 3-O-methylation that converts the pterocarpanoid isoflavonoid 6a-hydroxymaackiain to pisatin. In pea, pisatin is important for chemical resistance to the pathogenic fungus Nectria hematococca. While barrel medic does not biosynthesize 6a-hydroxymaackiain, when cell suspension cultures are fed 6a-hydroxymaackiain, they accumulate pisatin. In vitro, hydroxyisoflavanone 4'-O-methyltransferase (HI4'OMT) from barrel medic exhibits nearly identical steady state kinetic parameters for the 4'-O-methylation of the isoflavonoid intermediate 2,7,4'-trihydroxyisoflavanone and for the 3-O-methylation of the 6a-hydroxymaackiain isoflavonoid-derived pterocarpanoid intermediate found in pea. Protein x-ray crystal structures of HI4'OMT substrate complexes revealed identically bound conformations for the 2S,3R-stereoisomer of 2,7,4'-trihydroxyisoflavanone and the 6aR,11aR-stereoisomer of 6a-hydroxymaackiain. These results suggest how similar conformations intrinsic to seemingly distinct chemical substrates allowed leguminous plants to use homologous enzymes for two different biosynthetic reactions. The three-dimensional similarity of natural small molecules represents one explanation for how plants may rapidly recruit enzymes for new biosynthetic reactions in response to changing physiological and ecological pressures.
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==About this Structure==
==About this Structure==
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[[Category: Isoflavanone 4'-o-methyltransferase]]
[[Category: Isoflavanone 4'-o-methyltransferase]]
[[Category: Rossman fold]]
[[Category: Rossman fold]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 17:34:37 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Jul 27 17:31:23 2008''

Revision as of 14:31, 27 July 2008

Image:1zg3.png

Template:STRUCTURE 1zg3

Crystal structure of the isoflavanone 4'-O-methyltransferase complexed with SAH and 2,7,4'-trihydroxyisoflavanone

Template:ABSTRACT PUBMED 17172354

About this Structure

1ZG3 is a Single protein structure of sequence from Medicago truncatula. Full crystallographic information is available from OCA.

Reference

Structural basis for dual functionality of isoflavonoid O-methyltransferases in the evolution of plant defense responses., Liu CJ, Deavours BE, Richard SB, Ferrer JL, Blount JW, Huhman D, Dixon RA, Noel JP, Plant Cell. 2006 Dec;18(12):3656-69. Epub 2006 Dec 15. PMID:17172354

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