MetaCyc Enzyme: versiconal cyclase

Gene: vbs Accession Number: G-10727 (MetaCyc)

Synonyms: aflK

Species: Aspergillus parasiticus

Subunit composition of versiconal cyclase = [Vbs]2
         versiconal cyclase subunit = Vbs

The native apparent molecular mass was determined by gel filtration chromatography [McGuire96].

There is evidence that the product of Aspergillus parasiticus gene vbs can catalyze both this reaction and the 5'-oxoaverantin cyclase reaction in the aflatoxin biosynthesis pathway [Sakuno05] (see superpathway of aflatoxin biosynthesis). This suggests that one enzyme may catalyze two different reactions in a secondary metabolic pathway [Sakuno05].

This enzyme is strictly stereospecific for the (2'S) configuration of versiconal. Although this substrate is racemic, the (2'R) spontaneously forms the (2'S) configuration under physiological conditions. This produces optically pure versicolorin B and determines the configuration of the bisfuran ring system of sterigmatocystin and the aflatoxins in the aflatoxin biosynthesis pathway. This configuration is essential to the interaction of the metabolically activated aflatoxin product with DNA ([Yabe93], in [McGuire96, Sakuno05] and reviewed in [Yabe04]). See superpathway of aflatoxin biosynthesis.

The native enzyme is extensively glycosylated. The deduced protein sequence of recombinant enzyme expressed in Saccharomyces cerevisiae showed three potential N-linked glycosylation sites [Silva97].
The apparent molecular mass of the subunit was determined by SDS-PAGE [McGuire96].

Gene Citations: [Silva96, Yu04]

Molecular Weight of Polypeptide: 70.721 kD (from nucleotide sequence), 78.0 kD (experimental) [McGuire96 ]

Molecular Weight of Multimer: 140.0 kD (experimental) [McGuire96]

pI: 3.95 [Lin92a]

Unification Links: Protein Model Portal:Q12062 , UniProt:Q12062

Relationship Links: Entrez-Nucleotide:RELATED-TO:AY371490 , InterPro:IN-FAMILY:IPR000172 , InterPro:IN-FAMILY:IPR007867 , InterPro:IN-FAMILY:IPR012132 , Pfam:IN-FAMILY:PF00732 , Pfam:IN-FAMILY:PF05199 , Prosite:IN-FAMILY:PS00623 , Prosite:IN-FAMILY:PS00624

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Created 27-Jun-2008 by Fulcher CA , SRI International

Enzymatic reaction of: versiconal cyclase

Synonyms: versicolorin B synthase

EC Number:

versiconal <=> versicolorin B + H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the direction shown.

In Pathways: superpathway of aflatoxin biosynthesis , versicolorin B biosynthesis

The Km value is relatively low for a secondary metabolic enzyme and indicates a high affinity of the enzyme for its substrate [McGuire96].

Inhibitors (Unknown Mechanism): versicolorin B [McGuire96]

Kinetic Parameters:

Km (μM)

pH(opt): 5.5 [Lin92a]


Lin92a: Lin BK, Anderson JA (1992). "Purification and properties of versiconal cyclase from Aspergillus parasiticus." Arch Biochem Biophys 293(1);67-70. PMID: 1731640

McGuire96: McGuire SM, Silva JC, Casillas EG, Townsend CA (1996). "Purification and characterization of versicolorin B synthase from Aspergillus parasiticus. Catalysis of the stereodifferentiating cyclization in aflatoxin biosynthesis essential to DNA interaction." Biochemistry 35(35);11470-86. PMID: 8784203

Sakuno05: Sakuno E, Wen Y, Hatabayashi H, Arai H, Aoki C, Yabe K, Nakajima H (2005). "Aspergillus parasiticus cyclase catalyzes two dehydration steps in aflatoxin biosynthesis." Appl Environ Microbiol 71(6);2999-3006. PMID: 15932995

Silva96: Silva JC, Minto RE, Barry CE, Holland KA, Townsend CA (1996). "Isolation and characterization of the versicolorin B synthase gene from Aspergillus parasiticus. Expansion of the aflatoxin b1 biosynthetic gene cluster." J Biol Chem 271(23);13600-8. PMID: 8662689

Silva97: Silva JC, Townsend CA (1997). "Heterologous expression, isolation, and characterization of versicolorin B synthase from Aspergillus parasiticus. A key enzyme in the aflatoxin B1 biosynthetic pathway." J Biol Chem 272(2);804-13. PMID: 8995367

Yabe04: Yabe K, Nakajima H (2004). "Enzyme reactions and genes in aflatoxin biosynthesis." Appl Microbiol Biotechnol 64(6);745-55. PMID: 15022028

Yabe93: Yabe K, Hamasaki T (1993). "Stereochemistry during aflatoxin biosynthesis: cyclase reaction in the conversion of versiconal to versicolorin B and racemization of versiconal hemiacetal acetate." Appl Environ Microbiol 59(8);2493-500. PMID: 8368837

Yu04: Yu J, Chang PK, Ehrlich KC, Cary JW, Bhatnagar D, Cleveland TE, Payne GA, Linz JE, Woloshuk CP, Bennett JW (2004). "Clustered pathway genes in aflatoxin biosynthesis." Appl Environ Microbiol 70(3);1253-62. PMID: 15006741

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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