Protein: Versicolorin B synthase stcN (EC 4.2.1.143) (5'-oxoaverantin cyclase stcN) (EC 4.2.1.142) (Sterigmatocystin biosynthesis cluster protein N) (C8VDT4)
Organism: Emericella nidulans (strain FGSC A4 / ATCC 38163 / CBS 112.46 / NRRL 194 / M139) (Aspergillus nidulans)
Function: Norsolorinic acid reductase; part of the gene cluster that mediates the biosynthesis of sterigmatocystin (ST), a polyketide-derived furanocoumarin which is part of the most toxic and carcinogenic compounds among the known mycotoxins. The first step in the biosynthesis of sterigmatocystin is the production of hexanoate by the fatty acid synthase (FAS) units stcJ and stcK. The polyketide backbone is assembled by the non-reducing polyketide synthase stcA by condensation of the starter hexanoyl-CoA and 7 malonyl-CoA extender units followed by cyclization and release of norsolorinic acid (By similarity). Norsolorinic acid is the first stable intermediate in the biosynthesis of sterigmatocystin and is converted into averantin (AVN) by the ketoreductase stcE which reduces the hexanoate ketone to an alcohol (Probable). Averantin is then oxidized into 5'-hydroxyaverantin (HAVN) by the cytochrome P450 monooxygenase stcF. 5'-hydroxyaverantin is further converted to 5'-oxyaverantin (OAVN) by the 5'-hydroxyaverantin dehydrogenase stcG. The next step is the conversion of OAVN into averufin (AVF) which is catalyzed by a yet to be identified enzyme. The cytochrome P450 monoxygenase stcB and the flavin-binding monooxygenase stcW are both required for the conversion of averufin to 1-hydroxyversicolorone. The esterase stcI probably catalyzes the formation of versiconal hemiacetal acetate from 1-hydroxyversicolorone. The oxydoreductase stcN then probably catalyzes the biosynthetic step from versiconal to versicolorin B (VERB). The next step is performed by the versicolorin B desaturase stcL to produce versicolorin A (VERA). The ketoreductase stcU and the cytochrome P450 monooxygenase stcS are involved in the conversion of versicolorin A to demethylsterigmatocystin. The Baeyer-Villiger oxidas stcQ and the reductase stcR might be involved in the biosynthetic step from versicolorin A to demethylsterigmatocystin. The final step in the biosynthesis of sterigmatocystin is the methylation of demethylsterigmatocystin catalyzed by the methyltransferase stcP.
Subcellular location: Cytoplasm, cytosol {ECO:0000250|UniProtKB:Q12062}.
Interaction partners:
- Alpha/beta hydrolase fold-3 domain-containing protein
- Versiconal hemiacetal acetate esterase stcI
- Uncharacterized protein.
Sequence:
MPAWSLLVLSALPVVGMFAGQTTFFSSPWETLFGTAAEQHEAAMDGRIQGRGLLSSHFGWYGWPGQTFDYVIVGGGTAGLAMAHRLSEDGSNSVAVIEAGGFYEIEAGNATEVPMFLFNYFFDNGHVKNPLFDWYQYTEAQPGLAGRKMFYMQGKTLGGSTARGAMLYHRGSKGAYQLWADRVGDDSYTWDNWLPFFKKSVQFSGPLTNPRPANATASNDVSAFAATAEEEGPVQVAYPYLTNAISSWVDKALEKMGFPEAQGFSNGQLLGRSYITHTIHPKTRRRDTASTSYLQTALRTSNSLNVITHTLVKKIDFDEEKRATGVVVNTGGFEWQIGAKKEVILSAGVMRSPQLLMVSGLGPRETLEKLDIPVLSDLPGVGQNMQDTIILGPTNPVKVESHSQLMGSKETLPRSIYEYNNFRTGLLTNPGQDYFAFEKHQPGNLSEATAADIDKAFPADWPTFSYIALDDTFVPQYDGKNYFSMSAALLATFSRGTVTINTTNTADNPVVDPRWLDDPRDKEMAVAAFRRCREIVASETMQQVIDGPELLPGFEYQTDEEILNYIAETSDAYYAGVGTCAMGKPDDPLAVLDSKARVRGVKGLRVVDASAFPFAIDGQPMATVYALAEKVAADIIAGN