1ZHF

Crystal structure of selenomethionine substituted isoflavanone 4'-O-methyltransferase

Summary for 1ZHF

• Entry DOI: 10.2210/pdb1zhf/pdb
• Related: 1ZG3 1ZGA 1ZGJ
• Descriptor: Isoflavanone 4'-O-methyltransferase, S-ADENOSYL-L-HOMOCYSTEINE (3 entities in total)
• Functional Keywords: isoflavanone 4'-o-methyltransferase, rossmann fold, plant protein, transferase
• Biological source: Medicago truncatula (barrel medic)
• Total number of polymer chains: 1
• Total formula weight: 40480.06

Authors

Liu, C.-J.,Deavours, B.E.,Richard, S.,Ferrer, J.-L.,Dixon, R.A.,Noel, J.P. (deposition date: 2005-04-25, release date: 2006-08-01, Last modification date: 2024-02-14)

Primary citation

Liu, C.J.,Deavours, B.E.,Richard, S.B.,Ferrer, J.L.,Blount, J.W.,Huhman, D.,Dixon, R.A.,Noel, J.P.
Structural basis for dual functionality of isoflavonoid O-methyltransferases in the evolution of plant defense responses.
Plant Cell, 18:3656-3669, 2006

PubMed Abstract: 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.

PubMed: 17172354
DOI: 10.1105/tpc.106.041376

Experimental method

X-RAY DIFFRACTION (2.5 Å)