Abstract
Streptomyces are producers of valuable secondary metabolites with unique scaffolds that perform a plethora of biological functions. Nonribosomal peptides are of special interest due to their variety and complexity. They are synthesized by nonribosomal peptide synthetases, large biosynthetic machineries that are encoded in the genome of many Streptomyces species. The identification of new peptides and the corresponding biosynthetic gene clusters is of major interest since knowledge can be used to facilitate combinatorial biosynthesis and chemical semisynthesis of natural products. The recently discovered bosamycins are linear octapeptides with an interesting 5-OMe tyrosine moiety and various modifications at the N-terminus. In this study, the new cyclic depsibosamycins B, C, and D from Streptomyces aurantiacus LU19075 were discovered. In comparison to the linear bosamycins B, C, and D, which were also produced by the strain, the cyclic depsibosamycins showed a side-chain-to-tail lactonization of serine and glycine, leading to a ring of four amino acids. In silico identification and heterologous expression of the depsibosamycin (dbm) gene cluster indicated that the cyclic peptides, rather than the linear derivatives, are the main products of the cluster.
Highlights
Valérie LeclèreStreptomyces are known to produce valuable secondary metabolites with a plethora of unique structural classes [1,2]
Streptomyces aurantiacus LU19075 caught our attention due due to the production of a large quantity of compounds that were identified as well deto the production of a large quantity of compounds that were identified as well described scribed members of the nactin family (Figure 2) [18]
Determination of the Direct Biosynthetic Product of the dbm Gene Cluster. Both the linear bosamycins and the cyclic depsibosamycins have been identified in the strain S. aurantiacus LU19074, while only linear derivatives were reported in a previous study [9]
Summary
Streptomyces are known to produce valuable secondary metabolites with a plethora of unique structural classes [1,2] These compounds often express a variety of biological functions, which are the product of centuries of evolutionary design to develop a selective advantage for the strain [3]. Biosynthesis is initiated by the A-domain, which activates natural or modified amino acids. The condensation reaction with another amino acid, selected by an adjacent module, is catalyzed by the C-domain. Structure studies revealed a side-chain-to-tail lactonizationlactonization of serine andofglycine within the structure elucidation studies revealed a side-chain-to-tail serine and glycine within depsibosamycin This led to aThis ring including four amino acids, a feature hasthat the structure depsibosamycin.
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