10.10 A Sesterterpenoid Produced by an Artificially
Engineered Enzyme
In many cases, fungal sesterterpene synthases (C 25 ) and diterpene synthases (C 20 )
exist as chimeric enzymes, composed of a terpene cyclase and a prenyltransferase
[126, 127]. In other words, the terpene cyclase and the prenyltransferase are linked
together (Fig. 112). The reactions catalyzed by these two enzymes are shown in
Figs. 5–7. The fusion of these two enzymes is considered to provide a catalytic
8
OPP
PPO
H
157
158
H
Fig. 111 Structures and formation of somaliensenes A (157) and B (158)
Prenyltransferase
Terpene Cyclase
N-termimus
C-termimus
Linker
OPP
OH
8
OPP
8
95
3
4 4
OPP
OPP
cyclization
chain elongation
Fig. 112 Constitution of
the fungal chimeric
diterpene synthase and
sesterterpene synthase. The
chimeric terpene synthase
consists of two domains.
The C-terminal domain
possesses the
prenyltransferase activity,
while the N-terminal
domain exhibits the terpene
cyclase activity
64
T. Mitsuhashi and I. Abe