Protonation of a neutral (S)-beta-bisabolene intermediate is involved in (S)-beta-macrocarpene formation by the maize sesquiterpene synthases TPS6 and TPS11.
Terpene synthases are responsible for the large diversity of terpene carbon skeletons found in plants. The unique, carbocationic reaction mechanism of these enzymes can form multiple products from a single prenyl diphosphate substrate. Two maize genes were isolated that encode very similar sesquiterpene synthases, TPS6 and TPS11, which both produce beta-bisabolene, a common monocyclic sesquiterpene, and beta-macrocarpene, an uncommon bicyclic olefin. Investigation of the reaction mechanism showed that the formation of beta-macrocarpene proceeds via a neutral beta-bisabolene intermediate and requires reprotonation by a proton that may ultimately be abstracted from water. This reprotonation is dependent on the pH and the presence of a Mg(2+) cofactor. Mutational analysis of the enzyme demonstrated that a highly conserved tyrosine residue in the active center of the enzymes is important for the protonation process. TPS6 and TPS11 are transcribed both in leaves and roots of maize, but the respective terpene products were only detected in roots. The expression in roots was up-regulated by herbivore damage to the leaves, suggesting a long distance signal transduction cascade between leaves and roots.
Max Planck Institute for Chemical Ecology, Hans-Knöll Strasse 8, Jena, Germany.
Tobias G
TG
Köllner
Christiane
C
Schnee
Shenghong
S
Li
Ales
A
Svatos
Bernd
B
Schneider
Jonathan
J
Gershenzon
Jörg
J
Degenhardt
D019883:Alkyl and Aryl Transferases / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D004252:DNA Mutational Analysis; D018506:Gene Expression Regulation, Plant; D005964:Glucosyltransferases / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000737:chemistry; D008969:Molecular Sequence Data; D000081222:Monocyclic Sesquiterpenes; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D011522:Protons; D017386:Sequence Homology, Amino Acid; D012717:Sesquiterpenes / Q000737:chemistry*; D003313:Zea mays / Q000201:enzymology* / Q000378:metabolism
D000081222:Monocyclic Sesquiterpenes; D011522:Protons; D012717:Sesquiterpenes; C531190:beta-macrocarpene; D005964:Glucosyltransferases; D019883:Alkyl and Aryl Transferases; C108877:terpene synthase; D008274:Magnesium; C531191:beta-bisabolene