Fungal biosynthesis of non-ribosomal peptide antibiotics and α, α-dialkylated amino acid constituents

Abstract

Zervamicins (Zrv) IIA and IIB are membrane modifying peptide antibiotics of fungal origin, characterized by a sequence of 15 amino acid residues. The primary structure of Zrv-IIA contains five alpha-aminoisobutyric acid residues at positions 4, 7, 9, 12 and 14 of the linear peptide. The sequence of Zrv-IIB is similar, but contains a D-isovaline at position 4. When the free amino acid Aib was added to the peptone-glucose culture medium, the fungus Emericellopsis salmosynnemata produced Zrv-IIA as the major secondary metabolite, whereas addition of DL-Iva to the culture led to a high production of Zrv-IIB. This observation is rationalized by a lack of selectivity of the non-ribosomal peptide synthetase with respect to the thiolester activated amino acid substrates during step 12 of peptide synthesis. Analysis of the configuration of the Iva residue of Zrv-IIB showed a high enantiomeric purity of the D-enantiomer, indicating a high stereoselectivity of the peptide synthetase for this substrate.When the culture was supplemented with [(15)N]DL-Iva, the nitrogen isotope was not only found at the D-Iva residue, but surprisingly also at the Aib residues as well as at the proteinogenic residues of Zrv. The partial catabolism of exogenous [(15)N]DL-Iva is explained by the assumption of a decarboxylation-dependent transamination reaction, catalysed by 2,2-dimethylglycine decarboxylase. The same enzyme might also be involved in the reversed carboxylation reactions of acetone and 2-butanone, during the anabolic biosynthesis of Aib and Iva, respectively. Zrv might possibly act as a thermodynamic sink to shift these equilibrium reactions towards the reversed side.

Characterization of lignocellulolytic activities from fungi isolated from the deep-sea sponge Stelletta normani

“…Moreover Emericellopsis spp. have also been isolated from different marine macroalgae and sponges and have previously been studied due to their ability to produce non-ribosomal peptide antibiotics [11,86–90]. They have also recently been reported to influence the community structure in photosynthetic microbial mats, by degrading the top photoautotrophic layer of these intertidal hypersaline mats [91].…”

Biosynthesis and Molecular Genetics of Peptaibiotics—Fungal Peptides Containing Alpha, Alpha-Dialkyl Amino Acids

“…Kubicek et al [16] and Raap et al [65] proposed two likely pathways for Aib formation. In one, Aib is formed by its ste-reochemical neighbor, e.g., L-alanine, which would imply one or (in the case of lisovaline) two methyltransferase reactions, using adenosyl-methionine as a methyl group donor [16,65]. However, these hypotheses require confirmation by molecular genetic evidence.…”

“…Moreover, the addition of Aib to the culture of a T. harzianum strain generated new peptaibol molecules, in which all Iva residues were replaced by Aib, while the Glu-supply favored the synthesis of acidic longibrachins of T. longibrachiatum [67]. When free Aib or Iva is added to culture medium, the ratio between the peptaibols of Emericellopsis salmosynnemata can be manipulated [65]. If Aib is added, E. salmosynnemata produces Zrv-IIA as the major secondary metabolite, whereas the addition of DL-Iva to the culture increases the production of Zrv-IIB.…”

“…The function of these α (alpha), α (alpha)-dialkyl amino acids is to promote the formation of helical structures and to increase the resistance to proteolytic degradation [65]. However, the biosynthesis of these two special amino acids has not been studied extensively in peptaibiotic-producing strains.…”

Neuroleptic Properties of the Ion‐Channel‐Forming Peptaibol Zervamicin: Locomotor Activity and Behavioral Effects

“…Depending on the fungus strain, Emericellopsis salmosynnemata can produce eleven isoforms of zervamicin, with zervamicin IIA (Zrv-IIA) and zervamicin IIB (Zrv-IIB) as the major products [6] [7]. The primary structures of the Zrv-IIA and Zrv-IIB, distinct from each other by one residue at position 4, are as follows:…”