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Comment

Non-reducing polyketide synthase\; part of the gene cluster that mediates the biosynthesis of andrastins, meroterpenoid compounds that exhibit inhibitory activity against ras farnesyltransferase, suggesting that they could be promising leads for antitumor agents. The first step of the pathway is the synthesis of 3,5-dimethylorsellinic acid (DMOA) by the polyketide synthase adrD via condensation of one acetyl-CoA starter unit with 3 malonyl-CoA units and 2 methylations. DMAO is then converted to farnesyl-DMAO by the prenyltransferase adrG. The methyltransferase adrK catalyzes the methylation of the carboxyl group of farnesyl-DMAO to farnesyl-DMAO methyl ester which is further converted to epoxyfarnesyl-DMAO methyl ester by the FAD-dependent monooxygenase adrH. The terpene cyclase adrI then catalyzes the carbon skeletal rearrangement to generate the andrastin E, the first compound in the pathway having the andrastin scaffold, with the tetracyclic ring system. The post-cyclization tailoring enzymes adrF, adrE, adrJ, and adrA, are involved in the conversion of andrastin E into andrastin A. The short chain dehydrogenase adrF is responsible for the oxidation of the C-3 a hydroxyl group of andrastin E to yield the corresponding ketone, andrastin D. The ketoreductase adrE stereoselectively reduces the carbonyl moiety to reverse the stereochemistry of the C-3 position to yield andrastin F. The acetyltransferase adrJ is the acetyltransferase that attaches the acetyl group to the C-3 hydroxyl group of andrastin F to yield andrastin C. Finally, the cytochrome P450 monooxygenase adrA catalyzes two sequential oxidation reactions of the C-23 methyl group, to generate the corresponding alcohol andrastin B, and aldehyde andrastin A