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Title: Calcium-dependent antibiotics : directed biosynthesis and mechanistic studies
Author: Heidari, B. A.
ISNI:       0000 0004 2679 0370
Awarding Body: The University of Manchester
Current Institution: University of Manchester
Date of Award: 2007
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Calcium-dependent antibiotics (CDA) are acidic lipopeptides produced nonribosomally by the soil bacterium Streptomyces coelicolor. CDA is a cyclic undecapeptide lactone with an unusual 2,3-epoxyhexanoyl fatty acid side chain. CDAs are structurally very similar to the antibiotic daptomycin (Cubicin®), which is currently in use for the treatment of skin infections caused by Gram positive pathogens such as MRSA. The CDA biosynthetic gene cluster has been fully sequenced. This cluster contains open reading frames (ORF) which encode three megasynthases (CdaPS1-3) involved in the incorporation of the 11 amino acids, the enzymes responsible for fatty acid incorporation (fab operon), and a number of enzymes putatively responsible for the biosynthesis of amino acid precursors and for peptide modifications. The work described in this dissertation aims to delineate the biosynthetic pathways and mechanisms involved in the production and modification of CDA, specifically hydroxylation of asparagines, inclusion of the fatty acid moiety, and side chain dehydrogenation of tryptophan. The strategies exploited include substrate specificity investigations using a purified recombinant enzyme, classical stereochemical studies using stereospecific 2H labelling and 13C-2H dual labelling, and mutation-enforced precursor-directed biosynthesis. Mutant strains derived from CDA producing parent strains are used. Organic synthesis methodologies are employed to provide substrates and LC-MS and NMR are utilized for analysis. The investigations revealed the stereochemical course of tryptophan dehydrogenation as an overall Syn mechanism via a direct dehydrogenation. Moreover, mechanistic implications of fatty acid incorporation especially chain length limitation were highlighted. Furthermore, the research resulted in the production of novel CDA derivatives, containing modified fatty acid tails or tryptophan analogues.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available