Biosynthesis and biosynthetic engineering of calcium-dependent lipopeptide antibiotics

Abstract

Biosynthetic engineering involves the reprogramming of genes that are involved in the biosynthesis of natural products to generate new "non-natural" products, which might otherwise not exist in nature. Potentially this approach can be used to provide large numbers of secondary metabolite variants, with altered biological activities, many of which are too complex for effective total synthesis. Recently we have been investigating the biosynthesis of the calcium-dependent antibiotics (CDAs) which are members of the therapeutically relevant class of acidic lipopeptide antibiotics. CDAs are assembled by nonribosomal peptide synthetase (NRPS) enzymes. These large modular assembly-line enzymes process intermediates that are covalently tethered to peptidyl carrier protein (PCP) domain bonds, which makes them particularly amenable to reprogramming. The CDA producer, Streptomyces coelicolor, is also a genetically tractable model organism which makes CDAs an ideal template for biosynthetic engineering. To this end, we have elucidated many of the key steps in CDA biosynthesis and utilized this information to develop methods that have enabled the engineered biosynthesis of a wide range of CDA-type lipopeptides.

Solid-Phase Total Synthesis of Dehydrotryptophan-Bearing Cyclic Peptides Tunicyclin B, Sclerotide A, CDA3a, and CDA4a using a Protected β-Hydroxytryptophan Building Block

“…Like daptomycin, the CDAs are biosynthesized by NRPS. 109 Three subunits of the NRP synthetases CdaPS1, CdaPS2 and CdaPS3 are involved in the synthesis of the antibiotics. These subunits possess a modular organization and are composed of repeating condensation (C), adenylation (A), and thiolation (T) domains.…”

“…These subunits possess a modular organization and are composed of repeating condensation (C), adenylation (A), and thiolation (T) domains. 109 These CAT domains facilitate the addition of amino acids to the growing peptide. Several modules are flanked by epimerization domains that are involved in the formation of D-configured amino acids, such as D-HOAsn.…”

“…Researchers have speculated that the biosynthetic pathway begins at the epoxidated lipid where it is bound to the CdaPS1 subunit by a C domain (Figure 3.3). 107,109 Figure 3.3. First steps in the biosynthesis of CDAs.…”

“…The 2,3-epoxyhexanoyl fatty side chain, biosynthesized from Fatty Acid Synthetase (FAS), oxidase (HxcO) and monooxygenase (HcmO) enzymes, is transferred to CdaPSI enzyme of NRPS. 109 Researchers have determined that the Z-dehydrotryptophan of the CDAs is likely produced through direct dehydrogenation of a Trp residue in a fashion similar to that of the enzyme L-tryptophan -oxidase from Chromobacterium violaceum. 31 Similarly, the D-amino acids as well as the MeGlu residues are incorporated directly into the growing CDA peptide using epimerization and adenylation domains respectively.…”

Isolation and structure elucidation of lipopeptide antibiotic taromycin B from the activated taromycin biosynthetic gene cluster

“…6 The aspartic acid residue Asp-7 allows for coordination of Ca 2+ in a 1:1 stoichiometric ratio, resulting in daptomycin aggregation in the cytoplasmic membrane of Gram-positive bacteria. 7…”