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So, you want to know about siderophore synthesis Presented by: Steven Backues Brooks Maki and Donnie Berkholz “The Invisible Man”
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Hydroxamic Acid Groups N-Alkylation of O-substituted Hydroxamic acid. Formation of an oxime from an aldehyde and a hydroxylamine. Followed by reduction and acylation These derivatives allowed synthesis of several siderophores and their analogues
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Alternative Methods Oxidation of Lysine and OrnithineWith DMD (dimethyldioxarine) Conversion of primary amines to imines, with oxidation of imines to oxaziridines. Hydrolysis leads to hydroxylamines. D-Ferrichrome synthesized by this method
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Danoxamine Composed of a linear series of three hydroxamic acids. Composed of two major groups linked by succinic acid.
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Biosynthesis of Siderophores How it’s really done.
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Hydroxamate Siderophores
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Step 1: Ornithine N 5 - Oxygenase The formation of the N-O bond is the first committed step in hydroxamate synthesis Ornithine, an amino acid used in the urea cycle, is reacted with O 2 and NADPH to give an N-O bond at the end of its side chain.
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Step 2: N 5- Transacylase The nitrogen modified in this way is additionally attached to an acyl group carried by coenzyme A This completes the hydroxamate prosthetic group
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The Hydroxamate prosthetic group :
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Step 3: Non-ribosomal Peptide Synthetase This synthetase is a large complex with many subdomains, including an adenylation domain, a thiolation domain, and a condensation domain.
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Adenylation First, the hydroxamate is is activated by addition of an adenylate group at its C terminus The source of the adenylate group is ATP, and the reaction occurs with production of pyrophosphate
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Thiolation The hydroxamate group is then transferred to the enzyme through the formation of a thioester linkage with displacement of the adenylate group.
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Condensation Finally, the hydroxamate group is attached to another molecule (perhaps another hydroxamate group, or else a growing chain) by the nucleophilic attack of an OH or NH from the chain on the S-linked carbonyl, displacing the sulfur.
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Cathechols: Vibriobactin Vibriobactin is a siderophore used by Vibrio cholerae Its synthesis also involves a large, non- ribosomal peptide synthetase, and follows many of the same pathways as the synthesis of hydroxamate siderophores outlined above.
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Vibriobactin
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The Cathechol Prosthetic Group The cathechol prosthetic group is 2,3- dihydroxybenzoic acid, which is formed from chorismic acid
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Nonribosomal Peptide Synthetase 2,3-dihydrobenzoic acid then acts as a substrate for Vibirobactin Syntetase It is first activated by adenylation, then transferred to the enzyme with formation of a thioester
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Transfer to Norspermidine This thioester complex then undergoes nucleophilic attack by a primary amine on norspermidine. The norspermidine/cathechol complex goes on to react with two more cathechol prosthetic groups (these, however, attached by threonine derived linkages) to form the final siderophore
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Norspermidine+cathecol
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Yersiniabactin
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Synthesis Although it has neither hydroxamate nor cathechol groups, Yersiniabactin follows some of the same synthesis pathways, using a nonribosomal peptide sythetase that has clear homologies with, for example, vibriobactin sythetase
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Beginnings Synthesis begins with salicylic acid (2- hydroxy-benzoic acid) This is activated by the attachment of an adenylate group, then loaded onto the enzyme by the formation of a thioester, as before
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Elongation At the same time, two cystines are also activated then loaded onto the same enzyme, also via a thioester linkage Then, in the condensation/cyclization domain, the salicyate group is transferred onto one of the cystines, which is then cyclized. This cyclization is an unusual property of this particular synthetaes
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Completion A second cystine is added, and also cyclized, and the resulting molecule undergoes the addition of a malonyl group, S- adenosylmethionine, and an additional cystine to complete the synthesis
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Overview: The use of a large, multidomain nonribosomal peptide synthetase was a common element of all of these syntheses. All of these processes included the activation of a substrate by adenylation and the transfer to a thioester linkage with the enzyme, followed by condensation to form a longer chain. This is similar to the process followed in biosynthesis of fatty acids.
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References Roosenberg, J.M. and Miller, M.J. Total Synthesis of the Siderophore Danoxamine. J. Org. Chem. 2000 Vol. 65 No. 16. 4833 – 4838. Lin, Y. and Miller, M.J. Synthesis of Siderophore Components by and Indirect Oxidation Method. J. Org. Chem. 1999 Vol. 64 No. 20. 7451 – 7458. Gaspar, M., Grazina, R., Bodor, A., Farkas, E., and Santos, M.A. Macrocyclic tetraamine tris(hydroxamate) ligand. J. Chem Soc. 1999 799 – 806. Duhme, A.K. Synthesis of two dioxomolybdenum complexes of a siderophore analogue. J. Chem. Soc. 1997 773 – 778. Atkinson, A. Bacterial Iron Transport. Biochemistry. 1998. 15965 - 15973
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