title: Quantitative exploration of the catalytic landscape separating divergent plant sesquiterpene synthases.
abstract: Throughout molecular evolution, organisms create assorted chemicals in response to varying ecological niches. Catalytic landscapes underlie metabolic evolution, wherein mutational steps alter the biosynthetic properties of enzymes. Here we report the first systematic quantitative characterization of the catalytic landscape underlying the evolution of sesquiterpene chemical diversity. On the basis of our previous discovery of a set of nine naturally occurring amino acid substitutions that functionally interconverted orthologous sesquiterpene synthases from Nicotiana tabacum and Hyoscyamus muticus, we created a library of all possible residue combinations (2(9) = 512) in the N. tabacum enzyme. The product spectra of 418 active enzymes revealed a rugged landscape where several minimal combinations of the nine mutations encode convergent solutions to the interconversions of parental activities. Quantitative comparisons indicated context dependence for mutational effects--epistasis--in product specificity and promiscuity. These results provide a measure of the mutational accessibility of phenotypic variability in a diverging lineage of terpene synthases.
authors.affiliation: Howard Hughes Medical Institute, The Salk Institute for Biological Studies, Jack H. Skirball Center for Chemical Biology & Proteomics, 10010 North Torrey Pines Road, La Jolla, California 92037, USA.
authors.forename: Paul E
authors.initials: PE
authors.lastname: O'Maille
authors.forename: Arthur
authors.initials: A
authors.lastname: Malone
authors.forename: Nikki
authors.initials: N
authors.lastname: Dellas
authors.forename: B
authors.initials: B
authors.lastname: Andes Hess
authors.forename: Lidia
authors.initials: L
authors.lastname: Smentek
authors.forename: Iseult
authors.initials: I
authors.lastname: Sheehan
authors.forename: Bryan T
authors.initials: BT
authors.lastname: Greenhagen
authors.forename: Joe
authors.initials: J
authors.lastname: Chappell
authors.forename: Gerard
authors.initials: G
authors.lastname: Manning
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Noel
mesh_terms: D000595:Amino Acid Sequence; D019755:Carbon-Carbon Lyases / Q000737:chemistry* / Q000235:genetics*; D002384:Catalysis; D019143:Evolution, Molecular; D015723:Gene Library; D032304:Hyoscyamus / Q000737:chemistry / Q000201:enzymology / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016296:Mutagenesis; D010802:Phylogeny; D010936:Plant Extracts / Q000737:chemistry; D016415:Sequence Alignment; D014026:Nicotiana / Q000737:chemistry / Q000201:enzymology / Q000235:genetics*
chemical_list: D010936:Plant Extracts; D019755:Carbon-Carbon Lyases; C051130:trichodiene synthetase
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