posted on 2016-12-05, 00:00authored byJeffrey
D. Rudolf, Liao-Bin Dong, Karina Manoogian, Ben Shen
Platensimycin
(PTM) and platencin (PTN) are highly functionalized
bacterial diterpenoid natural products that target bacterial and mammalian
fatty acid synthases. PTM and PTN feature varying diterpene-derived
ketolides that are linked to the same 3-amino-2,4-dihydroxybenzoic
acid moiety. As a result, PTM is a selective inhibitor for FabF/FabB,
while PTN is a dual inhibitor of FabF/FabB and FabH. We previously
determined that the PTM cassette, consisting of five genes found in
the ptm, but not ptn, gene cluster,
partitions the biosynthesis of the PTM and PTN diterpene-derived ketolides.
We now report investigation of the PTM cassette through the construction
of diterpene production systems in E. coli and genetic
manipulation in the PTM–PTN dual overproducer Streptomyces
platensis SB12029, revealing two genes, ptmT3 and ptmO5, that are responsible for the biosynthetic
divergence between the PTM and PTN diterpene-derived ketolides. PtmT3,
a type I diterpene synthase, was determined to be a (16R)-ent-kauran-16-ol synthase, the first of its kind
found in bacteria. PtmO5, a cytochrome P450 monooxygenase, is proposed
to catalyze the formation of the characteristic 11S,16S-ether ring found in PTM. Inactivation of ptmO5 in SB12029 afforded the ΔptmO5 mutant SB12036 that accumulated nine PTM and PTN congeners, seven
of which were new, including seven 11-deoxy-16R-hydroxy-PTM
congeners. The two fully processed PTM analogues showed antibacterial
activities, albeit lower than that of PTM, indicating that the ether
ring, or minimally the stereochemistry of the hydroxyl group at C-16,
is crucial for the activity of PTM.