1zg3

[[Image:1zg3.gif|left|200px]]

|PDB= 1zg3 |SIZE=350|CAPTION= <scene name='initialview01'>1zg3</scene>, resolution 2.35&Aring;

|SITE=

|LIGAND= <scene name='pdbligand=2HI:(2S,3R)-2,7-DIHYDROXY-3-(4-HYDROXYPHENYL)-2,3-DIHYDRO-4H-CHROMEN-4-ONE'>2HI</scene> and <scene name='pdbligand=SAH:S-ADENOSYL-L-HOMOCYSTEINE'>SAH</scene>

|ACTIVITY=

|GENE= OMT ([http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&srchmode=5&id=3880 Medicago truncatula])

 

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

 

 

==Overview==

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.

 

==About this Structure==

1ZG3 is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Medicago_truncatula Medicago truncatula]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1ZG3 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:[http://www.ncbi.nlm.nih.gov/pubmed/17172354 17172354]

[[Category: Deavours, B E.]]

[[Category: Dixon, R A.]]

[[Category: Ferrer, J L.]]

[[Category: Liu, C J.]]

[[Category: Noel, J P.]]

[[Category: Richard, S.]]