ABSTRACT
Daptomycin is a lipopeptide antibiotic produced by a nonribosomal peptide synthetase (NRPS) in Streptomyces roseosporus. The holoenzyme is composed of three subunits, encoded by the dptA, dptBC, and dptD genes, each responsible for incorporating particular amino acids into the peptide. We introduced expression plasmids carrying dptD or NRPS genes encoding subunits from two related lipopeptide biosynthetic pathways into a daptomycin nonproducing strain of S. roseosporus harboring a deletion of dptD. All constructs successfully complemented the deletion in trans, generating three peptide cores related to daptomycin. When these were coupled with incomplete methylation of 1 amino acid and natural variation in the lipid side chain, 18 lipopeptides were generated. Substantial amounts of nine of these compounds were readily obtained by fermentation, and all displayed antibacterial activity against gram-positive pathogens.
Subject(s)
Anti-Bacterial Agents/pharmacology , Genetic Engineering , Lipoproteins/pharmacology , Peptide Synthases/metabolism , Streptomyces/metabolism , Amino Acid Sequence , Anti-Bacterial Agents/biosynthesis , Base Sequence , Cloning, Molecular , Daptomycin/chemistry , Daptomycin/pharmacology , Gram-Positive Bacterial Infections/drug therapy , Lipoproteins/biosynthesis , Lipoproteins/chemistry , Methylation , Molecular Sequence Data , Multigene Family , Peptide Synthases/chemistry , Peptide Synthases/genetics , Plasmids , Protein Subunits , Streptomyces/geneticsABSTRACT
Daptomycin and the A21978C antibiotic complex are lipopeptides produced by Streptomyces roseosporus and also in recombinant Streptomyces lividans TK23 and TK64 strains, when a 128 kbp region of cloned S. roseosporus DNA containing the daptomycin gene cluster is inserted site-specifically in the phiC31 attB site. A21978C fermentation yields were initially much lower in S. lividans than in S. roseosporus, and detection was complicated by the production of host metabolites. However A21978C production in S. lividans was improved by deletion of genes encoding the production of actinorhodin and by medium optimization to control the chemical form of the calcium dependent antibiotic (CDA). This latter compound has not previously been chemically characterized as a S. lividans product. Adding phosphate to a defined fermentation medium resulted in formation of only the phosphorylated forms of CDA, which were well separated from A21978C on chromatographic analysis. Adjusting the level of phosphate in the medium led to an improvement in A21978C yield from 20 to 55 mg/l.
Subject(s)
Anti-Bacterial Agents/metabolism , Daptomycin/biosynthesis , Peptides/metabolism , Recombinant Proteins/metabolism , Streptomyces lividans/metabolism , Streptomyces/metabolism , Anthraquinones/metabolism , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Calcium/metabolism , Culture Media , Daptomycin/chemistry , Fermentation , Gene Deletion , Intercellular Signaling Peptides and Proteins , Multigene Family , Peptides/chemistry , Streptomyces/genetics , Streptomyces lividans/geneticsABSTRACT
Daptomycin is a 13 amino acid, cyclic lipopeptide produced by a non-ribosomal peptide synthetase (NRPS) mechanism in Streptomyces roseosporus. A 128 kb region of S. roseosporus DNA was cloned and verified by heterologous expression in Streptomyces lividans to contain the daptomycin biosynthetic gene cluster (dpt). The cloned region was completely sequenced and three genes (dptA, dptBC, dptD) encoding the three subunits of an NRPS were identified. The catalytic domains in the subunits, predicted to couple five, six or two amino acids, respectively, included a novel activation domain and amino-acid-binding pocket for incorporating the unusual amino acid l-kynurenine (Kyn), three types of condensation domains and an extra epimerase domain (E-domain) in the second module. Novel genes (dptE, dptF) whose products likely work in conjunction with a unique condensation domain to acylate the first amino acid, as well as other genes (dptI, dptJ) probably involved in supply of the non-proteinogenic amino acids l-3-methylglutamic acid and Kyn, were located next to the NRPS genes. The unexpected E-domain suggested that daptomycin would have d-Asn, rather than l-Asn, as originally assigned, and this was confirmed by comparing stereospecific synthetic peptides and the natural product both chemically and microbiologically.
