Q2I0M6 · CTB3_CERNC

Function

function

Dual O-methyltransferase/FAD-dependent monooxygenase; part of the gene cluster that mediates the biosynthesis of cercosporin, a light-activated, non-host-selective toxin (PubMed:15915645, PubMed:17074519, 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 (PubMed:11701851).
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 in concert with the multicopper oxidase CTB12 are responsible for homodimerization of naphthalene with CTB7 installing the dioxepine moiety, finally producing cercosporin (PubMed:17660442, PubMed:26938470, PubMed:30809363).
The fasciclin domain-containing protein CTB11 might act with CTB5 and CTB12 whereas the roles of CTB9 and CTB10 have still to be elucidated (By similarity).

Catalytic activity

Pathway

Mycotoxin biosynthesis.

Features

Showing features for binding site, active site.

Type
IDPosition(s)Description
Binding site279S-adenosyl-L-methionine (UniProtKB | ChEBI)
Active site331Proton acceptor
Binding site485FAD (UniProtKB | ChEBI)
Binding site569FAD (UniProtKB | ChEBI)
Binding site806FAD (UniProtKB | ChEBI)

GO annotations

AspectTerm
Molecular Functionmonooxygenase activity
Molecular FunctionO-methyltransferase activity
Biological Processbiosynthetic process
Biological Processmethylation

Keywords

Names & Taxonomy

Protein names

  • Recommended name
    Dual O-methyltransferase/FAD-dependent monooxygenase CTB3
  • Alternative names
    • Cercosporin toxin biosynthesis cluster protein 3

Including 2 domains:

  • Recommended name
    O-methyltransferase
  • EC number
  • Recommended name
    FAD-dependent monooxygenase
  • EC number

Gene names

    • Name
      CTB3

Organism names

Accessions

  • Primary accession
    Q2I0M6

Phenotypes & Variants

Disruption phenotype

Abolishes the production of cercosporin but accumulates the naphthopyrones nor-toralactone and toralactone, as well as the oxidation product of nor-toralactone, naphthoquinone (PubMed:17074519, PubMed:26938470).
Adopts a dark yellow-brown coloration, with slight export of pigmented metabolites into the agar (PubMed:26938470).

Miscellaneous

PTM/Processing

Features

Showing features for chain.

TypeIDPosition(s)Description
ChainPRO_00004449671-871Dual O-methyltransferase/FAD-dependent monooxygenase CTB3

Expression

Induction

Expression is positively regulated by the cercosporin cluster-specific transcription factor CTB8 (PubMed:17462021).
Expression is also affected by nitrogen and carbon sources and pH, and is also controlled by another transcription activator, CRG1, previously shown to regulate cercosporin production and resistance (PubMed:17462021).

Structure

Family & Domains

Features

Showing features for region.

TypeIDPosition(s)Description
Region1-429O-methyltransferase
Region430-871FAD-dependent monooxygenase

Sequence similarities

In the C-terminal section; belongs to the paxM FAD-dependent monooxygenase family.

Family and domain databases

Sequence

  • Sequence status
    Complete
  • Length
    871
  • Mass (Da)
    95,728
  • Last updated
    2006-05-02 v2
  • Checksum
    7F7DD803CE5EE066
MMQFQRDLEASLEAVSANAQELLKSLKSRKDVQDLNASLPKDPLDNCDAQTQAARAQLAEAATRILQLSIRPQEYLEHLQNGYQHLTCFRWLVELNILDHLPHSGTISYTDLARKASVPPMQLRSICRMAICNGFLEEPEANQVRHSRISALFARDESYLGWARWMVNYSVPAAYKLSDATRSWGETVAKDQTAFNLGMDVKVPFFDHLRQTPAMKDAFAAYMRNVTSNATWGLQHAVTGFDWASLPRGAKVVDVGGSLGHGSIAIAKEHTHLTFVIQDLPETVAGARKEMAQNDKIEASVKSRITFQEHDFFGPQTVKDADVYFLRMICHDWPDNEAKVILSQIRAALKPGAQIVIMDTILPQPGTISVLQEQQLRIRDLTMMEVFNAKERELEDWSSLMQSAGLEISRVNQPLNSVMGLLTVRSAGQTALSGTNTLTPELVAAVSASTGSADSRPVLIAGAGIAGLCLAQALKKAGIDFRVFERDSHIDARPQGYRLKFEADAAQSLKNILPDDVYEAFELSNAVTAVGETDFNPFNGNIIHSRTGGGLSGKKGLYATFTVDRKAFRTQLMTGIEDKISFGKEIAYYKTDDATSTVNAEFKDGTHVTGSFLAGTDGLHSVVRKTCVPNHRIVDTGAACIYGKTVMTPEFLARFPEKGLRFMTVVSDIAPMLQSCLIGDSPVTLLLEPIRFSEASRARYPELPPDYVYWALIGPKERFGSQEVTSMKNFVSLDQAAEQAAKLSLAVTEEWHPSLRALFELQDTKQASLIRVASTIPDIPSWESHSNVTVLGGSIHPMSPCGGVGANTAIVDADALAKVLVEHGTKPPVNAIAEFGAAMRTRAKRNIWRSEVGSKRMFGQKNLVDCSEFVF

Sequence databases

Nucleotide SequenceProtein SequenceMolecule TypeStatus
DQ355149
EMBL· GenBank· DDBJ
ABC79591.2
EMBL· GenBank· DDBJ
Genomic DNA

Similar Proteins

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