- Thioesterase from Cereulide Biosynthesis Is Responsible for Oligomerization and Macrocyclization of a Linear Tetradepsipeptide
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Cereulide is a toxic cyclic depsidodecapeptide produced in Bacillus cereus by two nonribosomal peptide synthetases, CesA and CesB. While highly similar in structure to valinomycin and with a homologous biosynthetic gene cluster, recent work suggests that cereulide is produced via a different mechanism that relies on a noncanonical coupling of two didepsipeptide-peptidyl carrier protein (PCP) bound intermediates. Ultimately this alternative mechanism generates a tetradepsipeptide-PCP bound intermediate that differs from the tetradepsipeptide-PCP intermediate predicted from canonical activity of CesA and CesB. To differentiate between the mechanisms, both tetradepsipeptides were prepared as N-acetyl cysteamine thioesters (SNAC), and the ability of the purified recombinant terminal CesB thioesterase (CesB TE) to oligomerize and macrocyclize each substrate was probed. Only the canonical substrate is converted to cereulide, ruling out the alternative mechanism. It was demonstrated that CesB TE can use related tetradepsipeptide substrates, such as the valinomycin tetradespipetide and a hybrid cereulide-valinomycin tetradepsipetide in conjunction with its native substrate to generate chimeric natural products. This work clarifies the biosynthetic origins of cereulide and provides a powerful biocatalyst to access analogues of these ionophoric natural products.
- Boddy, Christopher N.,Heberlig, Graham W.
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supporting information
(2020/07/03)
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- ISOPROPENYL CHLOROCARBONATE (IPCC) IN AMINO ACID AND PEPTIDE CHEMISTRY: ESTERIFICATION OF N-PROTECTED AMINO ACIDS; APPLICATION TO THE SYNTHESIS OF THE DEPSIPEPTIDE VALINOMYCIN
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Esterification of N-protected α-amino acids was achieved via isopropenyl chlorocarbonate (IPCC) activation.In situ alcoholysis of the unstable mixed anhydride intermediate was catalised by 4-(dimethylamino)pyridine (DMAP).Competing isopropenyl ester formation was negligible when using methylene chloride as the solvent.A variety of esters from primary and secondary alcohols were obtained with good yields (60 to 90 percent), and even the more hindered tertiobutyl alcohol gave acceptable yields under more drastic conditions.The improvement in depsipeptide synthetic methodology is illustrated by preparation of the antibiotic valinomycin, using IPCC for ester bond formation, and BOP reagent for peptide coupling and the last-step cyclisation.
- Zeggaf, Choukri,Poncet, Joel,Jouin, Patrick,Dufour, Marie-Noelle,Castro, Bertrand
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p. 5039 - 5050
(2007/10/02)
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