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.Small molecule methyltransferases (MTs) are ubiquitous throughout the plant kingdom and methylate the hydroxyl, carboxyl, or nitrogen moieties of small molecules to form products which perform critical functions in plant defense, human nutrition and disease prevention. Type III plant MTs, also known as the SABATH (for Salicylic Acid, Benzoic Acid, Theobromine synthase) family of MTs, 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 compounds, a group which includes intermediates in caffeine and morphine biosynthesis. Our lab has made good progress in characterizing structures of plant MTs due to use of the SSRL facility: the first structure of a SABATH family member, Salicylic acid carboxyl methyltransferase (SAMT), an enzyme from Clarkia breweri with functions in floral scent and plant defense was solved to 3.0 resolution, and most recently, the first structure of an Arabidopsis thaliana SABATH family member, the Indole-3-acetic acid (auxin) carboxyl methyltransferase (IAMT) has been solved to 2.85 resolution. Active site modeling of the At Jasmonic acid carboxyl methyltransferase (JMT) based on the solved structure of the Clarkia SAMT allowed for the successful determination of critical JMT active site residues, and site-directed mutagenesis was used to create a bifunctional SAMT capable of using both salicylic acid and jasmonic acid as substrates. Active site modeling of the At Farnesoic acid methyltransferase (FAMT) has allowed for modulation of the acceptance of isoprenoid substrates with hydrocarbon tails of varying chain lengths. Our current goals are to structurally characterize the At FAMT, and another At SABATH family member which methylates gibberrellic acid, another plant hormone involved in all aspects of plant growth and development.
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