posted on 2021-02-12, 16:33authored byJie Zhang, Satoshi Yuzawa, Wei Li Thong, Tetsuro Shinada, Makoto Nishiyama, Tomohisa Kuzuyama
Natural products containing an o-dialkylbenzene
moiety exhibit a wide variety of bioactivities, including antibacterial,
antifungal, antitumor, and antiangiogenic activities. However, the
biosynthetic scheme of the o-dialkylbenzene moiety
remains unclear. In this study, we identified the biosynthetic gene
cluster (BGC) of compounds 1 and 2 in Streptomyces sp. SANK 60404, which contains a rare o-dialkylbenzene moiety, and successfully reconstituted
the biosynthesis of 1 using 22 recombinant enzymes in
vitro. Our study established a biosynthetic route for the o-tolyl group within the o-dialkylbenzene
moiety, where the triene intermediate 3 loaded onto a
unique acyl carrier protein (ACP) is elongated by a specific ketosynthase–chain
length factor pair of a type II polyketide synthase system with the
aid of a putative isomerase to be termed “electrocyclase”
and a thioesterase-like enzyme in the BGC. The C2-elongated
all-trans diketo–triene intermediate is subsequently isomerized
to the 6Z configuration by the electrocyclase to
allow intramolecular 6π-electrocyclization, followed by coenzyme
FAD/FMN-dependent dehydrogenation. Bioinformatics analysis showed
that the key genes are all conserved in BGCs of natural products containing
an o-dialkylbenzene moiety, suggesting that the proposed
biosynthetic scheme is a common strategy to form o-dialkylbenzenes in nature.