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==The cercosporin fungal non-reducing polyketide synthase (NR-PKS) CTB1 (SAT-KS-MAT)==
<StructureSection load='8by8' size='340' side='right'caption='[[8by8]], [[Resolution|resolution]] 2.50&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[8by8]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Cercospora_nicotianae Cercospora nicotianae]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=8BY8 OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=8BY8 FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">Electron Microscopy, [[Resolution|Resolution]] 2.5&#8491;</td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=8by8 FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=8by8 OCA], [https://pdbe.org/8by8 PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=8by8 RCSB], [https://www.ebi.ac.uk/pdbsum/8by8 PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=8by8 ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/CTB1_CERNC CTB1_CERNC] Polyketide synthase; part of the gene cluster that mediates the biosynthesis of cercosporin, a light-activated, non-host-selective toxin (PubMed:12937958, PubMed:15915645, PubMed:26938470, PubMed:29610486). 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, PubMed:29610486). 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, PubMed:29610486). 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:30809363, PubMed:26938470). 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]<ref>PMID:12937958</ref> <ref>PMID:15915645</ref> <ref>PMID:17074519</ref> <ref>PMID:17660442</ref> <ref>PMID:23108075</ref> <ref>PMID:26938470</ref> <ref>PMID:29610486</ref> <ref>PMID:30809363</ref> <ref>PMID:11701851</ref> 
== References ==
<references/>
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</StructureSection>
[[Category: Cercospora nicotianae]]
[[Category: Large Structures]]
[[Category: Maier T]]
[[Category: Munoz-Hernandez H]]