Abstract
Aflatoxins (AFs) are highly toxic and cancer-causing compounds, predominantly synthesized by the Aspergillus species. AFs biosynthesis is a lengthy process that requires as minimum as 30 genes grouped inside 75 kilobytes (kB) of gene clusters, which are regulated by specific transcription factors, including aflR, aflS, and some general transcription factors. This paper summarizes the status of research on characterizing structural and regulatory genes associated with AF production and their roles in aflatoxigenic fungi, particularly Aspergillus flavus and A. parasiticus, and enhances the current understanding of AFs that adversely affect humans and animals with a great emphasis on toxicity and preventive methods.
Highlights
Aflatoxins (AFs) are secondary metabolites predominantly synthesized by Aspergillus flavus and A. parasiticus
The term AF was given to the toxin since it was produced by A. flavus
AF exposure is closely related to increased risk of hepatocellular carcinoma (HCC), AIDS, stunting, and malnutrition in children in America, Asia, and Africa [6,7,8,9,10,11,12,13,14]
Summary
Aflatoxins (AFs) are secondary metabolites predominantly synthesized by Aspergillus flavus and A. parasiticus. NOR, an essential metabolite synthesized in the AF’s biosynthetic pathway, exhibits a red–orange color in mutant strains of aflD (nor-1) of A. parasiticus [26]. VAL Conversion to Versicolorin-B (VERB) AflK, a cyclase that catalyzes the cyclodehydration of VAL into VERB [23] This is a crucial phase in the AF’s biosynthetic pathway as the closure of the bisfuran ring occurs at this stage. VERB Conversion to Versicolorin A (VERA)-AFB1-AFG1 Pathway AflL, a monooxygenase of cytochrome P450, is responsible for converting the tetrahydrofuran ring to a dihydrobisfuran ring [34]. AflM, aflN, aflY, and aflX are putative enzymes involved in DMST formation in the biosynthetic pathway of AFB1-AFG1 [35]. The same enzymatic steps have been suggested in the biosynthetic pathway of AFB2-AFG2, but using VERB as a substrate rather than VERA, resulting in DHDMST formation. It is sensitive to temperature during incubation; the expressions of aflS and aflR were increased by 24 times at 30 ◦C compared to 37 ◦C [46]
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