Plant Physiol, May 2002, Vol. 129, pp. 257-268
Biosynthesis of Costunolide, Dihydrocostunolide, and Leucodin.
Demonstration of Cytochrome P450-Catalyzed Formation of the Lactone
Ring Present in Sesquiterpene Lactones of Chicory
Jan-Willem
de Kraker,
Maurice C.R.
Franssen,1*
Maaike
Joerink,
Aede
de Groot, and
Harro J.
Bouwmeester1
Laboratory of Organic Chemistry, Wageningen University,
Dreijenplein 8, 6703 HB Wageningen, The Netherlands (J.-W.d.K.,
M.C.R.F., M.J., A.d.G.); and Plant Research International, P.O. Box 16, 6700 AA Wageningen, The Netherlands (J.-W.d.K., M.J., H.J.B.)
Chicory (Cichorium intybus) is known to
contain guaianolides, eudesmanolides, and germacranolides. These
sesquiterpene lactones are postulated to originate from a common
germacranolide, namely (+)-costunolide. Whereas a pathway for the
formation of germacra-1(10),4,11(13)-trien-12-oic acid from farnesyl
diphosphate had previously been established, we now report the
isolation of an enzyme activity from chicory roots that converts the
germacrene acid into (+)-costunolide. This (+)-costunolide synthase
catalyzes the last step in the formation of the lactone ring present in
sesquiterpene lactones and is dependent on NADPH and molecular oxygen.
Incubation of the germacrene acid in the presence of
18O2 resulted in the incorporation of one atom
of 18O into (+)-costunolide. The label was situated at the
ring oxygen atom. Hence, formation of the lactone ring most likely
occurs via C6-hydroxylation of the germacrene acid and
subsequent attack of this hydroxyl group at the C12-atom of
the carboxyl group. Blue light-reversible CO inhibition and experiments
with cytochrome P450 inhibitors demonstrated that the (+)-costunolide
synthase is a cytochrome P450 enzyme. In addition, enzymatic conversion of (+)-costunolide into 11(S),13-dihydrocostunolide and
leucodin, a guaianolide, was detected. The first-mentioned reaction
involves an enoate reductase, whereas the formation of leucodin from
(+)-costunolide probably involves more than one enzyme, including a
cytochrome P450 enzyme.
1
These authors contributed equally to the paper.
*
Corresponding author; e-mail Maurice.Franssen{at}bio.oc.wag-ur.nl;
fax 31-317-484914.
© 2002 American Society of Plant Physiologists
