| IED ID | IndEnz0010000180 |
| Enzyme Type ID | esterase000180 |
| Protein Name |
Versicolorin B synthase EC 4.2.1.143 5'-oxoaverantin cyclase EC 4.2.1.142 Aflatoxin biosynthesis protein K |
| Gene Name | aflK vbs P875_00052980 |
| Organism | Aspergillus parasiticus (strain ATCC 56775 / NRRL 5862 / SRRC 143 / SU-1) |
| Taxonomic Lineage | cellular organisms Eukaryota Opisthokonta Fungi Dikarya Ascomycota saccharomyceta Pezizomycotina leotiomyceta Eurotiomycetes Eurotiomycetidae Eurotiales (green and blue molds) Aspergillaceae Aspergillus Aspergillus parasiticus Aspergillus parasiticus (strain ATCC 56775 / NRRL 5862 / SRRC 143 / SU-1) |
| Enzyme Sequence | MGRNWFQVTAMAVVPVVGIMAAVNPTILSSAASSLPSLGAMFTSDDFASQMDGRIQAQGLLSSHFGMYGWPGQSFDYVIVGGGTAGLAMARRLSQDGTASVAVIEAGGFYETDAGNATEVPMYLFNYFFDNGKVKNPLFDWYQYTTPQPGLAQREMFYMQGKTLGGSTARGAMLYHRGSKGAYDMWADHVGDDSYRWDKWLPYFQKSVHFSGPETNPRPANATALNDNTAFTASGGPVHVGYPFQVNAISSWVDRALAKMGFPEAQGFSNGNLLGRSYITHTINPYTRRRETASSSYLREALMESNNLNIFTRTLVKRVLFDDQNRATGVTVNTDGFEWQIGARKEVILSAGVMRSPQLLMVSGIGPKDHLEQLGIPVRSDLSGVGQNMQDTIILGPTVPVKVESHSQLMGNKETLPRAIREYNEQRKGLLTNPGQDYFAFEKHQPGMLKESTAADIDAAFPDDWPTFSYIALDDTFVPQYDGKNYFSMSAALMTPFSRGTVTINSNDTANPPIVDPQWLADPRDQEMAVAAFRRCREIVASDVMREVVAGPEILPGPQYQTDEEILNYIAETSDAYYAGVGTCAMGKADDPKAVVDSKARVLGVKGLRIVDASIFPFAIDGQPMGTVYALAEKIAAEMMAGQ |
| Enzyme Length | 643 |
| Uniprot Accession Number | Q12062 |
| Absorption | |
| Active Site | |
| Activity Regulation | |
| Binding Site | BINDING 613; /note=FAD; via amide nitrogen; /evidence=ECO:0000250|UniProtKB:E4QP00 |
| Calcium Binding | |
| catalytic Activity | CATALYTIC ACTIVITY: Reaction=(2S-3S)-versiconal hemiacetal = H2O + versicolorin B; Xref=Rhea:RHEA:33859, ChEBI:CHEBI:15377, ChEBI:CHEBI:77950, ChEBI:CHEBI:77951; EC=4.2.1.143; Evidence={ECO:0000269|PubMed:14602595, ECO:0000269|PubMed:15932995, ECO:0000269|PubMed:1731640, ECO:0000269|PubMed:8784203}; CATALYTIC ACTIVITY: Reaction=(S)-5'-oxoaverantin + H(+) = (1'S,5'S)-averufin + H2O; Xref=Rhea:RHEA:35671, ChEBI:CHEBI:15377, ChEBI:CHEBI:15378, ChEBI:CHEBI:71537, ChEBI:CHEBI:77933; EC=4.2.1.142; Evidence={ECO:0000269|PubMed:14602595, ECO:0000269|PubMed:15932995, ECO:0000269|PubMed:1731640, ECO:0000269|PubMed:8784203}; |
| DNA Binding | |
| EC Number | 4.2.1.143; 4.2.1.142 |
| Enzyme Function | FUNCTION: Versicolorin B synthase; part of the gene cluster that mediates the biosynthesis of aflatoxins, a group of polyketide-derived furanocoumarins, and part of the most toxic and carcinogenic compounds among the known mycotoxins (PubMed:15006741). The four major aflatoxins produced by A.parasiticus are aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin G1 (AFG1) and aflatoxin G2 (AFG2) (PubMed:15006741). The first step of the pathway is the conversion of acetate to norsolorinic acid (NOR) and requires the fatty acid synthase subunits aflA and aflB, as well as the PKS aflC (PubMed:15006741). AflC combines a hexanoyl starter unit and 7 malonyl-CoA extender units to synthesize the precursor NOR (PubMed:18403714). The hexanoyl starter unit is provided to the acyl-carrier protein (ACP) domain by the fungal fatty acid synthase aflA/aflB (PubMed:16256699). The second step is the conversion of NOR to averantin (AVN) and requires the norsolorinic acid ketoreductase aflD, which catalyzes the dehydration of norsolorinic acid to form (1'S)-averantin (PubMed:10584035). The norsolorinic acid reductases aflE and aflF may also play a role in the conversion of NOR to AVN (PubMed:15006741). The cytochrome P450 monooxygenase aflG then catalyzes the hydroxylation of AVN to 5'hydroxyaverantin (HAVN) (PubMed:8368836). The next step is performed by the 5'-hydroxyaverantin dehydrogenase aflH that transforms HAVN to 5'-oxoaverantin (OAVN) which is further converted to averufin (AVF) by aflK that plays a dual role in the pathway, as a 5'-oxoaverantin cyclase that mediates conversion of 5'-oxoaverantin, as well as a versicolorin B synthase in a later step in the pathway (PubMed:15006741, PubMed:11055914, PubMed:15932995). The averufin oxidase aflI catalyzes the conversion of AVF to versiconal hemiacetal acetate (VHA) (PubMed:15006741). VHA is then the substrate for the versiconal hemiacetal acetate esterase aflJ to yield versiconal (VAL) (PubMed:15006741). Versicolorin B synthase aflK then converts VAL to versicolorin B (VERB) by closing the bisfuran ring of aflatoxin which is required for DNA-binding, thus giving to aflatoxin its activity as a mutagen (PubMed:8662689, PubMed:15932995, PubMed:1731640, PubMed:8368837, PubMed:8784203, PubMed:14602595, PubMed:15006741). Then, the activity of the versicolorin B desaturase aflL leads to versicolorin A (VERA) (PubMed:15006741, PubMed:8368837). A branch point starts from VERB since it can also be converted to dihydrodemethylsterigmatocystin (DMDHST), probably also by aflL, VERA being a precursor for aflatoxins B1 and G1, and DMDHST for aflatoxins B2 and G2 (PubMed:15006741). Next, the versicolorin reductase aflM and the cytochrome P450 monooxygenase aflN are involved in conversion of VERA to demethylsterigmatocystin (DMST) (PubMed:15006741, PubMed:1339261, PubMed:15771506). AflX and aflY seem also involved in this step, through probable aflX-mediated epoxide ring-opening step following versicolorin A oxidation and aflY-mediated Baeyer-Villiger oxidation required for the formation of the xanthone ring (PubMed:16332900, PubMed:16461654). The methyltransferase aflO then leads to the modification of DMST to sterigmatocystin (ST), and of DMDHST to dihydrosterigmatocystin (DHST) (PubMed:10543813). Both ST and DHST are then substrates of the O-methyltransferase aflP to yield O-methylsterigmatocystin (OMST) and dihydro-O-methylsterigmatocystin (DHOMST), respectively (PubMed:8434913). Finally OMST is converted to aflatoxins B1 and G1, and DHOMST to aflatoxins B2 and G2, via the action of several enzymes including O-methylsterigmatocystin oxidoreductase aflQ, the cytochrome P450 monooxygenase aflU, but also the NADH-dependent flavin oxidoreductase nadA which is specifically required for the synthesis of AFG1 (PubMed:15006741, PubMed:11996570, PubMed:15528514, PubMed:18486503). {ECO:0000269|PubMed:10543813, ECO:0000269|PubMed:10584035, ECO:0000269|PubMed:11055914, ECO:0000269|PubMed:11996570, ECO:0000269|PubMed:1339261, ECO:0000269|PubMed:14602595, ECO:0000269|PubMed:15006741, ECO:0000269|PubMed:15528514, ECO:0000269|PubMed:15771506, ECO:0000269|PubMed:15932995, ECO:0000269|PubMed:16256699, ECO:0000269|PubMed:16332900, ECO:0000269|PubMed:16461654, ECO:0000269|PubMed:1731640, ECO:0000269|PubMed:18403714, ECO:0000269|PubMed:18486503, ECO:0000269|PubMed:8368836, ECO:0000269|PubMed:8368837, ECO:0000269|PubMed:8434913, ECO:0000269|PubMed:8662689, ECO:0000269|PubMed:8784203, ECO:0000305|PubMed:15006741}. |
| Temperature Dependency | |
| PH Dependency | BIOPHYSICOCHEMICAL PROPERTIES: pH dependence: Optimum pH is 5.5. {ECO:0000269|PubMed:14602595, ECO:0000269|PubMed:1731640}; |
| Pathway | PATHWAY: Mycotoxin biosynthesis; aflatoxin biosynthesis. {ECO:0000269|PubMed:15094053, ECO:0000305|PubMed:15006741}. |
| nucleotide Binding | NP_BIND 84..85; /note=FAD; /evidence=ECO:0000250|UniProtKB:E4QP00; NP_BIND 105..106; /note=FAD; /evidence=ECO:0000250|UniProtKB:E4QP00; NP_BIND 171..174; /note=FAD; /evidence=ECO:0000250|UniProtKB:E4QP00; NP_BIND 624..625; /note=FAD; /evidence=ECO:0000250|UniProtKB:E4QP00 |
| Features | Binding site (1); Chain (1); Glycosylation (3); Nucleotide binding (4); Propeptide (1) |
| Keywords | Cytoplasm;Direct protein sequencing;FAD;Flavoprotein;Glycoprotein;Lyase;Reference proteome |
| Interact With | |
| Induction | |
| Subcellular Location | SUBCELLULAR LOCATION: Cytoplasm, cytosol {ECO:0000269|PubMed:14602595, ECO:0000305|PubMed:15932995}. |
| Modified Residue | |
| Post Translational Modification | PTM: N-glycosylated. {ECO:0000269|PubMed:8995367}. |
| Signal Peptide | |
| Structure 3D | |
| Cross Reference PDB | - |
| Mapped Pubmed ID | - |
| Motif | |
| Gene Encoded By | |
| Mass | 70,271 |
| Kinetics | BIOPHYSICOCHEMICAL PROPERTIES: Kinetic parameters: KM=20 uM for 5'-oxoaverantin {ECO:0000269|PubMed:14602595, ECO:0000269|PubMed:1731640}; KM=3.1 uM for versiconal (at pH 6.0 and 30 degrees Celsius) {ECO:0000269|PubMed:14602595, ECO:0000269|PubMed:1731640}; Vmax=6.67 nmol/min/mg enzyme with 5'-oxoaverantin as substrate {ECO:0000269|PubMed:14602595, ECO:0000269|PubMed:1731640}; Vmax=0.15 umol/min/mg enzyme with versiconal (at pH 6.0 and 30 degrees Celsius) as substrate {ECO:0000269|PubMed:14602595, ECO:0000269|PubMed:1731640}; |
| Metal Binding | |
| Rhea ID | RHEA:33859; RHEA:35671 |
| Cross Reference Brenda | 4.2.1.142;4.2.1.143; |