Isomerase prhC

UniProtKB accession:  A0A1E1FFL1

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UniProtKB description:  Isomerase; part of the gene cluster that mediates the biosynthesis of paraherquonin, a meroterpenoid with a unique, highly congested hexacyclic molecular architecture (PubMed:27602587). The first step of the pathway is the synthesis of 3,5-dimethylorsellinic acid (DMOA) by the polyketide synthase prhL (By similarity). Synthesis of DMOA is followed by farnesylation by the prenyltransferase prhE, methylesterification by the methyl-transferase prhM, epoxidation of the prenyl chain by the flavin-dependent monooxygenase prhF, and cyclization of the farnesyl moiety by the terpene cyclase prhH, to yield the tetracyclic intermediate, protoaustinoid A (By similarity). The short chain dehydrogenase prhI then oxidizes the C-3 alcohol group of the terpene cyclase product to transform protoaustinoid A into protoaustinoid B (PubMed:27602587). The FAD-binding monooxygenase prhJ catalyzes the oxidation of protoaustinoid B into preaustinoid A which is further oxidized into preaustinoid A1 by FAD-binding monooxygenase phrK (PubMed:27602587). Finally, prhA leads to berkeleydione via the berkeleyone B intermediate (PubMed:27602587, PubMed:29317628). PrhA is a multifunctional dioxygenase that first desaturates at C5-C6 to form berkeleyone B, followed by rearrangement of the A/B-ring to form the cycloheptadiene moiety in berkeleydione (PubMed:27602587, PubMed:29317628). Berkeleydione serves as the key intermediate for the biosynthesis of paraherquonin as well as many other meroterpenoids (Probable). The cytochrome P450 monooxygenases prhB, prhD, and prhN, as well as the isomerase prhC, are probably involved in the late stage of paraherquonin biosynthesis, after the production of berkeleydione (Probable). Especially prhC might be a multifunctional enzyme that catalyzes the D-ring expansion via intramolecular methoxy rearrangement, as well as the hydrolysis of the expanded D-ring (Probable).