FAD-dependent monooxygenase; part of the gene cluster that mediates the biosynthesis of cercosporin, a light-activated, non-host-selective toxin (PubMed:17660442, PubMed:17462021, PubMed:26938470). The perylenequinone chromophore of cercosporin absorbs light energy to attain an electronically-activated triplet state and produces active oxygen species such as the hydroxyl radical, superoxide, hydrogen peroxide or singlet oxygen upon reaction with oxygen molecules. These reactive oxygen species cause damage to various cellular components including lipids, proteins and nucleic acids (PubMed:11701851). The first step of cercosporin biosynthesis is performed by the polyketide synthase CTB1 which catalyzes the formation of nor-toralactone (PubMed:23108075, PubMed:26938470). The starter unit acyltransferase (SAT) domain of CTB1 initiates polyketide extension by the selective utilization of acetyl-CoA, which is elongated to the heptaketide in the beta-ketoacyl synthase (KS) domain by successive condensations with six malonyl units introduced by the malonyl acyltransferase (MAT) domain. The product template (PT) domain catalyzes C4-C9 and C2-C11 aldol cyclizations and dehydrations to a trihydroxynaphthalene, which is thought to be delivered to the thioesterase (TE) domain for product release (PubMed:23108075). The bifunctional enzyme CTB3 then methylates nor-toralactone to toralactone before conducting an unusual oxidative aromatic ring opening (PubMed:17074519, PubMed:26938470). The O-methyltransferase CTB2 further methylates the nascent OH-6 of the CBT3 product, blocking further oxidation at this site before the reductase CTB6 reduces the 2-oxopropyl ketone at position C7, giving naphthalene (PubMed:17660442, PubMed:26938470). The FAD-dependent monooxygenase CTB5 is thought to be responsible for homodimerization of naphthalene with CTB7 installing the dioxepine moiety, finally producing cercosporin (PubMed:17660442, PubMed:26938470).

Belongs to the oxygen-dependent FAD-linked oxidoreductase family.

459 amino acids

MGSYFSLKNSDLHPSCIALPRSAEEVSKAVRTLSLGAHKWEGQCQFGVRGGGHTPFKGAASTDNGIVLDLLHMPSAGISPDYETITVSPSTTWDLVYEVLDAHNRSTLGTKVAGIGVGGASTSCGVSYFSPRYGYICDMVENWEVVLATGDIVNANANENADLWKALRGGINNFGIVTAVTLKAFEQGPFWGGQTFHSIETRQEHFKNHAKLASAHPYDPYAHYINTLVLANGGHWFIGNSIQYTKSDPPVAEPEVFKPFLKTERTPIFPGLPEDTLRVDNVTSFSREYAANTLYPQRWQFACISFAPDADFMETFFQMANDAMQQYVKLPGFKLILNYQPAPTVQLERNGAVDSLGPIQTEGNVVFVHWAVSYDESEAQFDDAITKSVQDLFHAANTKAKELGIYRHFIQPTYADSWQSPFDYRSKSTIEELVATSKKYDPLQVFQKQVPGGFKLPQI

50.8 kDa

(Note: Representative image - actual molecular weight may vary depending on tag type and expression method)

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