1m6e
From Proteopedia
CRYSTAL STRUCTURE OF SALICYLIC ACID CARBOXYL METHYLTRANSFERASE (SAMT)
Structural highlights
Function[SAMT_CLABR] Catalyzes the methylation of the free carboxyl end of the plant hormone salicylic acid (SA). Converts SA to SA methyl ester (MSA). The volatile compound MSA is hypothesized to act as an airborne signal that triggers defense responses in uninfected plants. MSA is an important chemoattractant for moth pollinated flowering plants. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedRecently, a novel family of methyltransferases was identified in plants. Some members of this newly discovered and recently characterized methyltransferase family catalyze the formation of small-molecule methyl esters using S-adenosyl-L-Met (SAM) as a methyl donor and carboxylic acid-bearing substrates as methyl acceptors. These enzymes include SAMT (SAM:salicylic acid carboxyl methyltransferase), BAMT (SAM:benzoic acid carboxyl methyltransferase), and JMT (SAM:jasmonic acid carboxyl methyltransferase). Moreover, other members of this family of plant methyltransferases have been found to catalyze the N-methylation of caffeine precursors. The 3.0-A crystal structure of Clarkia breweri SAMT in complex with the substrate salicylic acid and the demethylated product S-adenosyl-L-homocysteine reveals a protein structure that possesses a helical active site capping domain and a unique dimerization interface. In addition, the chemical determinants responsible for the selection of salicylic acid demonstrate the structural basis for facile variations of substrate selectivity among functionally characterized plant carboxyl-directed and nitrogen-directed methyltransferases and a growing set of related proteins that have yet to be examined biochemically. Using the three-dimensional structure of SAMT as a guide, we examined the substrate specificity of SAMT by site-directed mutagenesis and activity assays against 12 carboxyl-containing small molecules. Moreover, the utility of structural information for the functional characterization of this large family of plant methyltransferases was demonstrated by the discovery of an Arabidopsis methyltransferase that is specific for the carboxyl-bearing phytohormone indole-3-acetic acid. Structural basis for substrate recognition in the salicylic acid carboxyl methyltransferase family.,Zubieta C, Ross JR, Koscheski P, Yang Y, Pichersky E, Noel JP Plant Cell. 2003 Aug;15(8):1704-16. PMID:12897246[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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