This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.Plant small molecule O-methyltransferases (OMTs) are ubiquitous throughout the plant kingdom and methylate the hydroxyl and carboxyl moieties of small molecules to form compounds which perform critical functions in plant defense, and in human nutrition and disease prevention. While Type I OMTs methylate the hydroxyl groups of phenylpropanoid compounds to form flavonoids and isoflavonoids, which are known to function in UV protection, and in prevention of human heart disease, cancer, and osteoporosis, Type II OMTs are found in all plants that produce lignin which functions in plant defense, structural support, and provides pulp material for the paper industry. Type III plant OMTs convert small molecule carboxylic acids to their methyl esters, which have been shown to play vital roles in plant defense, signal transduction, floral scent, and development. This group also includes a subset of N-methyltransferases that target the nitrogen functionality of alkaloid small molecules, a group of compounds with important human pharmaceutical benefits. Our lab has made considerable progress in characterizing structures of plant OMTs due to use of the SSRL facility: we recently published the first structures of plant OMTs, those of Chalcone O-methyltransferase (ChOMT) and isoflavone O-methyltransferase (IOMT), two natural product methyltransferases that respectively produce compounds that serve as potent inducers of the soil rhizobia nodulation genes and the major anti-fungal phytoalexin in alfalfa, and the structure of Caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferase (COMT) from alfalfa, an enzyme involved in lignin biosynthesis. Most recently, the structure of Salicylic acid methyltransferase (SAMT), an enzyme from Clarkia breweri with functions in floral scent and plant defense was solved. Active site modeling of the Jasmonic acid carboxyl methyltransferase (JAMT) from Arabidopsis based on the solved structure of the Clarkia SAMT allowed for the success.
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