title: Conversion of substrate analogs suggests a Michael cyclization in iridoid biosynthesis.
abstract: The core structure of the iridoid monoterpenes is formed by a unique cyclization reaction. The enzyme that catalyzes this reaction, iridoid synthase, is mechanistically distinct from other terpene cyclases. Here we describe the synthesis of two substrate analogs to probe the mechanism of iridoid synthase. Enzymatic assay of these substrate analogs along with clues from the product profile of the native substrate strongly suggest that iridoid synthase utilizes a Michael reaction to achieve cyclization. This improved mechanistic understanding will facilitate the exploitation of the potential of iridoid synthase to synthesize new cyclic compounds from nonnatural substrates.
authors.affiliation: Department of Biological Chemistry, The John Innes Centre, Norwich NR4 7UH, UK; Institute of Organic Chemistry, Karlsruhe Institute of Technology, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Lindner
authors.affiliation: Institute of Organic Chemistry, Karlsruhe Institute of Technology, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany.
authors.forename: Fernando
authors.initials: F
authors.lastname: Geu-Flores
authors.affiliation: Institute of Organic Chemistry, Karlsruhe Institute of Technology, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany; Institute of Toxicology and Genetics, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bräse
authors.affiliation: Department of Biological Chemistry, The John Innes Centre, Norwich NR4 7UH, UK. Electronic address: nat.sherden@jic.ac.uk.
authors.forename: Nathaniel H
authors.initials: NH
authors.lastname: Sherden
authors.affiliation: Department of Biological Chemistry, The John Innes Centre, Norwich NR4 7UH, UK. Electronic address: sarah.oconnor@jic.ac.uk.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: O'Connor
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000378:metabolism*; D055162:Biocatalysis; D003500:Cyclization; D039823:Iridoids / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D009249:NADP / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity; D013729:Terpenes / Q000737:chemistry
chemical_list: D039823:Iridoids; D013729:Terpenes; D009249:NADP; D019883:Alkyl and Aryl Transferases