title: Plant polyketide synthases leading to stilbenoids have a domain catalyzing malonyl-CoA:CO2 exchange, malonyl-CoA decarboxylation, and covalent enzyme modification and a site for chain lengthening.
abstract: Stilbene synthases and the related bibenzyl synthases are plant polyketide synthases whose biological functions lie in the formation of antimicrobial phytoalexins. The formation of hydroxystilbenes from one molecule of acyl-CoA and three molecules of malonyl-CoA is catalyzed by a homodimeric 90 kDa protein and includes Claisen condensations and cleavage of a thioester followed by decarboxylation. Combining inhibitor studies, protein modifications, and site-directed mutagenesis, we were able to differentiate between the binding sites for malonyl-CoA and the regions responsible for the selection of the primer, p-coumaroyl-CoA or m-hydroxyphenylpropionyl-CoA, respectively. Mutations in the C-terminal part of the molecule or modification by photolabeling with p-azidocinnamoyl-CoA influence the overall reaction, the formation of hydroxystilbenes, but leave partial reactions, such as the malonyl-CoA:CO2 exchange and the malonyl-CoA-dependent modification of the enzyme, unaffected. Data obtained with several kinds of stilbene synthase and mutant forms suggest that the malonyl-CoA-dependent covalent modification takes place at a cysteine residue in the N-terminal part of the enzyme. Mutations in the C-terminal half of the enzyme molecule do not interfere with the malonyl-CoA-dependent reactions.
authors.affiliation: Fachbereich Chemie, Philipps-Universität, D-35032 Marburg, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Preisig-Müller
authors.forename: R
authors.initials: R
authors.lastname: Gehlert
authors.forename: F
authors.initials: F
authors.lastname: Melchior
authors.forename: U
authors.initials: U
authors.lastname: Stietz
authors.forename: H
authors.initials: H
authors.lastname: Kindl
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D000217:Acyltransferases / Q000378:metabolism; D000345:Affinity Labels; D000595:Amino Acid Sequence; D001665:Binding Sites; D002245:Carbon Dioxide / Q000378:metabolism*; D005033:Ethylmaleimide / Q000378:metabolism; D007700:Kinetics; D008316:Malonyl Coenzyme A / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism; D016296:Mutagenesis; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010666:Phenylpropionates / Q000378:metabolism; D010944:Plants / Q000201:enzymology*; D013267:Stilbenes / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: C106927:3-(3-hydroxyphenyl)propionyl-coenzyme A; D000214:Acyl Coenzyme A; D000345:Affinity Labels; D009097:Multienzyme Complexes; D010446:Peptide Fragments; D010666:Phenylpropionates; D013267:Stilbenes; D002245:Carbon Dioxide; D008316:Malonyl Coenzyme A; D000217:Acyltransferases; C022674:stilbene synthase; D005033:Ethylmaleimide