title: O-Methylation of benzaldehyde derivatives by "lignin specific" caffeic acid 3-O-methyltransferase.
abstract: Although S-adenosyl-l-methionine (SAM) dependent caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferase (COMT) is one of the key enzymes in lignin biosynthesis, the present work demonstrates that alfalfa COMT methylates benzaldehyde derivatives more efficiently than lignin pathway intermediates. 3,4-Dihydroxy, 5-methoxybenzaldehyde and protocatechuic aldehyde were the best in vitro substrates for OMT activity in extracts from developing alfalfa stems, and these compounds were preferred over lignin pathway intermediates for 3-O-methylation by recombinant alfalfa COMT expressed in Escherichia coli. OMT activity with benzaldehydes was strongly reduced in extracts from stems of transgenic alfalfa down-regulated in COMT. However, although COMT down-regulation drastically affects lignin composition, it does not appear to significantly impact metabolism of benzaldehyde derivatives in alfalfa. Structurally designed site-directed mutants of COMT showed altered relative substrate preferences for lignin precursors and benzaldehyde derivatives. Taken together, these results indicate that COMT may have more than one role in phenylpropanoid metabolism (but probably not in alfalfa), and that engineered COMT enzymes could be useful for metabolic engineering of both lignin and benzaldehyde-derived flavors and fragrances.
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA.
authors.forename: Parvathi
authors.initials: P
authors.lastname: Kota
authors.forename: Dianjing
authors.initials: D
authors.lastname: Guo
authors.forename: Chloe
authors.initials: C
authors.lastname: Zubieta
authors.forename: Joe
authors.initials: J
authors.lastname: Noel
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D019943:Amino Acid Substitution; D001547:Benzaldehydes / Q000737:chemistry / Q000378:metabolism*; D002250:Carbon Radioisotopes; D015536:Down-Regulation; D062385:Hydroxybenzoates / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008031:Lignin / Q000378:metabolism*; D000455:Medicago sativa / Q000201:enzymology / Q000235:genetics; D008745:Methylation; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D010636:Phenols / Q000737:chemistry / Q000378:metabolism; D018547:Plant Stems / Q000201:enzymology; D030821:Plants, Genetically Modified / Q000201:enzymology; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D001547:Benzaldehydes; D002250:Carbon Radioisotopes; D062385:Hydroxybenzoates; D010636:Phenols; D011994:Recombinant Proteins; C009091:protocatechuic acid; D012436:S-Adenosylmethionine; D008031:Lignin; D008780:Methyltransferases; C019608:caffeate O-methyltransferase