Abstract
Members of the fungal genus Fusarium can produce numerous secondary metabolites, including the nonribosomal mycotoxins beauvericin (BEA) and enniatins (ENNs). Both mycotoxins are synthesized by the multifunctional enzyme enniatin synthetase (ESYN1) that contains both peptide synthetase and S-adenosyl-l-methionine-dependent N-methyltransferase activities. Several Fusarium species can produce ENNs, BEA or both, but the mechanism(s) enabling these differential metabolic profiles is unknown. In this study, we analyzed the primary structure of ESYN1 by sequencing esyn1 transcripts from different Fusarium species. We measured ENNs and BEA production by ultra-performance liquid chromatography coupled with photodiode array and Acquity QDa mass detector (UPLC-PDA-QDa) analyses. We predicted protein structures, compared the predictions by multivariate analysis methods and found a striking correlation between BEA/ENN-producing profiles and ESYN1 three-dimensional structures. Structural differences in the β strand’s Asn789-Ala793 and His797-Asp802 portions of the amino acid adenylation domain can be used to distinguish BEA/ENN-producing Fusarium isolates from those that produce only ENN.
Highlights
Enniatins (ENNs) and beauvericin (BEA) are structurally-related mycotoxins (Figure 1) produced by several fungal species
We confirmed our working hypothesis that the difference in ENN and BEA chemotypes of the strains under study depends on the ESYN1 protein sequence and its three-dimensional structure
The novel analytical method in which UPLC was coupled with an MS-QDa detector resulted in a unique chromatographic run that could measure BEA and ENN levels in agar samples
Summary
Enniatins (ENNs) and beauvericin (BEA) are structurally-related mycotoxins (Figure 1) produced by several fungal species. These compounds have antibiotic and ionophoric properties and different bioactivities [1]. BEA and ENNs are non-ribosomal cyclic hexadepsipeptides that consist of alternating. The three amino acid residues are aromatic N-methyl-phenylalanines, whereas in type A and B enniatins, the amino acid residues are aliphatic N-methyl-valine, or N-methyl-isoleucine, or mixtures of these amino acids [2]. The subunits are linked by peptide bonds and intramolecular ester (lactone) bonds, forming a cyclic depsipeptide.
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