averufin and averantin

Eight anthraquinones (1-8), three xanthones (11-13) and two phenols (9-10) were isolated from Aspergillus sp. associated with Panax notoginseng, and their structures were determined as ziganein-1-methyl ether (1), 8-O-methylchrysophanol (2), averythrin (3), averufin (4), 8-O-methyl averufin (5), versicolorin B (6), averantin (7), methyl-averantin (8), arugosin C (9), diorcinol (10), sterigmatocystin (11), demethylsterigmatocystin (12) and dihydrosterigmatocystin (13) by spectroscopic analyses. Compounds 1, 2 and 5 were the novel isolates from genus Aspergillus. Compounds 3, 6 and 7 exhibited antifungal activity against Fusariumsolani, pathogenic fungus of P. notoginseng, with minimum inhibitory concentrations (MICs) of 16-32 μg/mL, and compounds 1, 3, 4, 7 and 9 showed antibacterial activity against Bacillussubtilis with MICs of 64-128 μg/mL, 16-32 μg/mL, 8-16 μg/mL, 16-32 μg/mL and 64-128 μg/mL, respectively. The metabolites showed the potential value in the research of antifungal agents, especially in searching for a biocontrol of diseases of P. notoginseng. The preliminary structure-activity relationships have been discussed for some of the compounds.

Topics: Anthraquinones; Anti-Bacterial Agents; Antifungal Agents; Aspergillus; Bacillus subtilis; Fusarium; Microbial Sensitivity Tests; Molecular Structure; Panax notoginseng; Structure-Activity Relationship; Xanthones

Sterigmatocystin (ST) and aflatoxin B(1) (AFB(1)) are two polyketide-derived Aspergillus mycotoxins synthesized by functionally identical sets of enzymes. ST, the compound produced by Aspergillus nidulans, is a late intermediate in the AFB(1) pathway of A. parasiticus and A. flavus. Previous biochemical studies predicted that five oxygenase steps are required for the formation of ST. A 60-kb ST gene cluster in A. nidulans contains five genes, stcB, stcF, stcL, stcS, and stcW, encoding putative monooxygenase activities. Prior research showed that stcL and stcS mutants accumulated versicolorins B and A, respectively. We now show that strains disrupted at stcF, encoding a P-450 monooxygenase similar to A. parasiticus avnA, accumulate averantin. Disruption of either StcB (a putative P-450 monooxygenase) or StcW (a putative flavin-requiring monooxygenase) led to the accumulation of averufin as determined by radiolabeled feeding and extraction studies.

Topics: Anthraquinones; Aspergillus nidulans; Cytochrome P-450 Enzyme System; Oxygenases; Sterigmatocystin; Transformation, Genetic

Recent studies have shown that at least 17 genes involved in the aflatoxin biosynthetic pathway are clustered within a 75-kb DNA fragment in the genome of Aspergillus parasiticus. Several additional transcripts have also been mapped to this gene cluster. A gene, avnA (previously named ord-1), corresponding to one of the two transcripts identified earlier between the ver-1 and omtA genes on the gene cluster was sequenced. The nucleotide sequence of the avnA gene contains a coding region for a protein of 495 amino acids with a calculated molecular mass of 56.3 kDa. The gene consists of three exons and two introns. Disruption of the avnA gene in the wild-type aflatoxigenic A. parasiticus strain (SU1-N3) resulted in a nonaflatoxigenic mutant which accumulated a bright yellow pigment. Thin-layer chromatographic studies with six different solvent systems showed that the migration patterns of the accumulated metabolite were identical to those of averantin, a known aflatoxin precursor. Precursor feeding studies with this mutant showed that norsolorinic acid and averantin were not converted to aflatoxin whereas 5'-hydroxyaverantin, averufanin, averufin, versicolorin A. sterigmatocystin, and O-methylsterigmatocystin were converted to aflatoxins. Southern blot analysis of the wild-type strain and avnA-disrupted mutant strain indicated that the avnA gene was disrupted in the mutant strain. A search of the GenBank database for similarity indicated that the avnA gene encodes a cytochrome P-450-type monooxygenase, and it has been assigned to a new P-450 gene family named CYP60A1. We have therefore concluded that the avnA gene encodes a fungal cytochrome P-450-type enzyme which is involved in the conversion of averantin to averufin in the aflatoxin biosynthetic pathway in A. parasiticus.

Topics: Aflatoxins; Amino Acid Sequence; Anthraquinones; Aspergillus; Base Sequence; Cytochrome P-450 Enzyme System; Gene Expression Regulation, Fungal; Genome, Fungal; Molecular Sequence Data; Multigene Family; Mutation

Wild-type Aspergillus parasiticus produces, in addition to the colorless aflatoxins, a number of pigmented secondary metabolites. Examination of these pigments demonstrated that a major component was an anthraquinone, averufanin. Radiolabeling studies with [14C]averufanin showed that 23% of the label was incorporated into aflatoxin B1 by the wild type and that 31% of the label was incorporated into O-methylsterigmatocystin by a non-aflatoxin-producing isolate. In similar studies with blocked mutants of A. parasiticus the 14C label from averufanin was accumulated in averufin (72%) and versicolorin A (54%) but not averantin. The results demonstrate that averufanin is a biosynthetic precursor of aflatoxin B1 between averantin and averufin.

Topics: Aflatoxin B1; Aflatoxins; Anthraquinones; Aspergillus; Pigments, Biological