title: A conserved amino acid residue critical for product and substrate specificity in plant triterpene synthases.
abstract: Triterpenes are structurally complex plant natural products with numerous medicinal applications. They are synthesized through an origami-like process that involves cyclization of the linear 30 carbon precursor 2,3-oxidosqualene into different triterpene scaffolds. Here, through a forward genetic screen in planta, we identify a conserved amino acid residue that determines product specificity in triterpene synthases from diverse plant species. Mutation of this residue results in a major change in triterpene cyclization, with production of tetracyclic rather than pentacyclic products. The mutated enzymes also use the more highly oxygenated substrate dioxidosqualene in preference to 2,3-oxidosqualene when expressed in yeast. Our discoveries provide new insights into triterpene cyclization, revealing hidden functional diversity within triterpene synthases. They further open up opportunities to engineer novel oxygenated triterpene scaffolds by manipulating the precursor supply.
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom;
authors.forename: Melissa
authors.initials: M
authors.lastname: Salmon
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom;
authors.forename: Ramesha B
authors.initials: RB
authors.lastname: Thimmappa
authors.affiliation: Department of Chemistry and Chemical Biology, Indiana University-Purdue University, Indianapolis, IN 46202;
authors.forename: Robert E
authors.initials: RE
authors.lastname: Minto
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom;
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Melton
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom;
authors.forename: Richard K
authors.identifier: 0000-0001-9910-6566
authors.initials: RK
authors.lastname: Hughes
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom; Food & Health Programme, Institute of Food Research, Norwich Research Park, Norwich NR4 7UH, United Kingdom;
authors.forename: Paul E
authors.initials: PE
authors.lastname: O'Maille
authors.affiliation: School of Chemistry, University of East Anglia, Norwich NR4 7TJ, United Kingdom; School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Hemmings
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom; anne.osbourn@jic.ac.uk.
authors.forename: Anne
authors.initials: A
authors.lastname: Osbourn
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry / Q000235:genetics*; D018554:Avena / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence / Q000235:genetics; D003500:Cyclization; D019751:Intramolecular Transferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000072417:Protein Domains; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014315:Triterpenes / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D010940:Plant Proteins; D014315:Triterpenes; D019751:Intramolecular Transferases; C039924:2,3-oxidosqualene-beta-amyrin-cyclase
keywords: cyclization; mutants; natural products; plant defense; terpenes