7eut

Structural highlights

Function

CTB9_CERBT Hydroxylase/desaturase; part of the gene cluster that mediates the biosynthesis of cercosporin, a light-activated, non-host-selective toxin (PubMed:29844193). 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 (Probable). 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 (Probable). The bifunctional enzyme CTB3 then methylates nor-toralactone to toralactone before conducting an unusual oxidative aromatic ring opening (Probable). 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 (Probable). 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 (Probable). 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).[UniProtKB:Q0UHZ9]^{[1] [2] [3]}

References

1. ↑ de Jonge R, Ebert MK, Huitt-Roehl CR, Pal P, Suttle JC, Spanner RE, Neubauer JD, Jurick WM 2nd, Stott KA, Secor GA, Thomma BPHJ, Van de Peer Y, Townsend CA, Bolton MD. Gene cluster conservation provides insight into cercosporin biosynthesis and extends production to the genus Colletotrichum. Proc Natl Acad Sci U S A. 2018 Jun 12;115(24):E5459-E5466. PMID:29844193 doi:10.1073/pnas.1712798115
2. ↑ Daub ME, Ehrenshaft M. The Photoactivated Cercospora Toxin Cercosporin: Contributions to Plant Disease and Fundamental Biology. Annu Rev Phytopathol. 2000 Sep;38:461-490. PMID:11701851 doi:10.1146/annurev.phyto.38.1.461
3. ↑ de Jonge R, Ebert MK, Huitt-Roehl CR, Pal P, Suttle JC, Spanner RE, Neubauer JD, Jurick WM 2nd, Stott KA, Secor GA, Thomma BPHJ, Van de Peer Y, Townsend CA, Bolton MD. Gene cluster conservation provides insight into cercosporin biosynthesis and extends production to the genus Colletotrichum. Proc Natl Acad Sci U S A. 2018 Jun 12;115(24):E5459-E5466. PMID:29844193 doi:10.1073/pnas.1712798115