An asparagine oxygenase (AsnO) and a 3-hydroxyasparaginyl phosphotranferase (HasP) are involved in the biosynthesis of calcium-dependent lipopeptide antibiotics

Nonribosomal peptides contain a wide range of unusual non-proteinogenic amino acid residues. As a result, these complex natural products are amongst the most structurally diverse secondary metabolites in nature, and possess a broad spectrum of biological activities. β-Hydroxylation of amino acid precursors or peptidyl residues and their subsequent processing by downstream tailoring enzymes are some of the most common themes in the biosynthetic diversification of these therapeutically important peptides. Identification and characterization of the biosynthetic intermediates and enzymes involved in these processes are thus pivotal in understanding nonribosomal peptide assembly and modification. To this end, the putative asparaginyl oxygenase- and 3-hydroxyasparaginyl phosphotransferase-encoding genes hasP and asnO were separately deleted from the calcium-dependent antibiotic (CDA) biosynthetic gene cluster of Streptomyces coelicolor. Whilst the parent strains produce a number of 3-hydroxyasparagine- and 3-phosphohydroxyasparagine-containing CDAs, the ΔhasP mutants produce exclusively non-phosphorylated CDAs. On the other hand, ΔasnO mutants produce several new Asn-containing CDAs not present in the wild-type, which retain calcium-dependent antimicrobial activity. This confirms that AsnO and HasP are required for the β-hydroxylation and phosphorylation of the Asn residue within CDA. © 2007 SGM.