barrel (DABB) protein that is structurally similar to polyketide cyclases found
amongStreptomycesspecies.
The recombinant OAC catalyzed the C2–C7 aldol condensation of the tetrake-
tide intermediate produced by olivetol synthase to form OLA (Fig.8.10b). OAC
formation was detected even when OAC was separated from olivetol synthase using
a dialysis membrane, demonstrating that OAC did not physically interact with
olivetol synthase. Thus, the role of olivetol synthase in OLA biosynthesis is to
supply a tetraketide intermediate, which then functions as a substrate for OAC.
Based on protein function, olivetol synthase is often referred to as tetraketide
synthase. It has also been reported that olivetol synthase accepts butyryl-CoA as an
alternative starter substrate to produce divarinol, a propyl side chain homologue of
olivetol (Taura et al. 2009b). Therefore, divarinolic acid, the precursor for
cannabinoids with a propyl side chain (de Zeeuw et al. 1972 ), might also be
biosynthesized by the co-action of olivetol synthase and OAC.
The identification of OAC not only clarified the largest mystery in the
cannabinoid pathway, but also suggested the possibility that OAC-like polyketide
cyclases might play an overlooked role in generating plant polyketide diversity,
since DABB proteins are widely distributed among various plant species (Gagne
et al. 2012 ). The necessity of accessory proteins has been proposed for the
biosynthesis of various polyketides, as plant polyketide synthases, alone, often
afford unexpected reaction products in vitro (Abe et al. 2005 ; Springob et al. 2007 ).
In addition, the OAC gene was essential for the biotechnological production of
OLA in heterologous hosts. Gagne et al. ( 2012 ) demonstrated that yeast cultures
expressing olivetol synthase and OAC produced 0.48 mg/L OLA upon feeding of
sodium hexanoate. Furthermore, the study on OAC was essential in the progress of
“the omics era”in relation to cannabinoid biosynthesis, as Page’s group has also
cloned genes for CsPT-1 and hexanoyl-CoA producing acyl-CoA synthase using a
transcriptome-based strategy, as in the case of OAC (Page and Boubakir 2011 ;
Stout et al. 2012 ).
Very recently, Morita’s group reported the crystal structure of OAC, demon-
strating the substrate recognition and catalytic mechanism of the only known plant
polyketide cyclase (Yang et al. 2016 ). Thus, in near future, the modification of the
OLA active site might provide polyketide cyclase enzymes with novel catalytic
functions.
8.3 Biotechnological Cannabinoid Production
Since complete cannabinoid biosynthesis was only recently elucidated, genetic
manipulation will be of great value to increase cannabinoid production. Together
with the draft genome and transcriptome ofC. sativa(van Bakel et al. 2011 ), this
valuable information could enable the wide biotechnological application of
cannabinoid production. In this section, we review and suggest various biotech-
nological applications for cannabinoid production.
8 Cannabinoids: Biosynthesis and Biotechnological Applications 197