title: Fungal biosynthesis of non-ribosomal peptide antibiotics and alpha, alpha-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.
authors.affiliation: Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands. J.Raap@chem.LeidenUniv.nl
authors.forename: Jan
authors.initials: J
authors.lastname: Raap
authors.forename: Kees
authors.initials: K
authors.lastname: Erkelens
authors.forename: Andrey
authors.initials: A
authors.lastname: Ogrel
authors.forename: Dmitri A
authors.initials: DA
authors.lastname: Skladnev
authors.forename: Hans
authors.initials: H
authors.lastname: Brückner
mesh_terms: D000478:Alkylation; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000900:Anti-Bacterial Agents / Q000138:chemical synthesis* / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D032641:Eurotiales / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D010455:Peptides; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D000596:Amino Acids; D000900:Anti-Bacterial Agents; D010455:Peptides