Streptolydigin

The Streptomyces lydicus

Amino acid precursor supply in the biosynthesis of the RNA polymerase inhibitor streptolydigin by Streptomyces lydicus.[Pubmed:21665968]

J Bacteriol. 2011 Aug;193(16):4214-23.

Biosynthesis of the hybrid polyketide-nonribosomal peptide antibiotic Streptolydigin, 3-methylaspartate, is utilized as precursor of the tetramic acid moiety. The three genes from the Streptomyces lydicus Streptolydigin gene cluster slgE1-slgE2-slgE3 are involved in 3-methylaspartate supply. SlgE3, a ferredoxin-dependent glutamate synthase, is responsible for the biosynthesis of glutamate from glutamine and 2-oxoglutarate. In addition to slgE3, housekeeping NADPH- and ferredoxin-dependent glutamate synthase genes have been identified in S. lydicus. The expression of slgE3 is increased up to 9-fold at the onset of Streptolydigin biosynthesis and later decreases to approximately 2-fold over the basal level. In contrast, the expression of housekeeping glutamate synthases decreases when Streptolydigin begins to be synthesized. SlgE1 and SlgE2 are the two subunits of a glutamate mutase that would convert glutamate into 3-methylaspartate. Deletion of slgE1-slgE2 led to the production of two compounds containing a lateral side chain derived from glutamate instead of 3-methylaspartate. Expression of this glutamate mutase also reaches a peak increase of up to 5.5-fold coinciding with the onset of antibiotic production. Overexpression of either slgE3 or slgE1-slgE2 in S. lydicus led to an increase in the yield of Streptolydigin.

Biosynthesis of the RNA polymerase inhibitor streptolydigin in Streptomyces lydicus: tailoring modification of 3-methyl-aspartate.[Pubmed:21398531]

J Bacteriol. 2011 May;193(10):2647-51.

The asparaginyl-tRNA synthetase-like SlgZ and methyltransferase SlgM enzymes are involved in the biosynthesis of the tetramic acid Streptolydigin in Streptomyces lydicus. Inactivation of slgZ led to a novel Streptolydigin derivative. Overexpression of slgZ, slgM, or both in S. lydicus led to a considerable increase in Streptolydigin production.

Antibiotic streptolydigin requires noncatalytic Mg2+ for binding to RNA polymerase.[Pubmed:24342645]

Antimicrob Agents Chemother. 2014;58(3):1420-4.

Multisubunit RNA polymerase, an enzyme that accomplishes transcription in all living organisms, is a potent target for antibiotics. The antibiotic Streptolydigin inhibits RNA polymerase by sequestering the active center in a catalytically inactive conformation. Here, we show that binding of Streptolydigin to RNA polymerase strictly depends on a noncatalytic magnesium ion which is likely chelated by the aspartate of the bridge helix of the active center. Substitutions of this aspartate may explain different sensitivities of bacterial RNA polymerases to Streptolydigin. These results provide the first evidence for the role of noncatalytic magnesium ions in the functioning of RNA polymerase and suggest new routes for the modification of existing and the design of new inhibitors of transcription.

Chemical synthesis enables biochemical and antibacterial evaluation of streptolydigin antibiotics.[Pubmed:21714556]

J Am Chem Soc. 2011 Aug 10;133(31):12172-84.

Inhibition of bacterial transcription represents an effective and clinically validated anti-infective chemotherapeutic strategy. We describe the evolution of our approach to the Streptolydigin class of antibiotics that target bacterial RNA polymerases (RNAPs). This effort resulted in the synthesis and biological evaluation of Streptolydigin, Streptolydiginone, streptolic acid, and a series of new Streptolydigin-based agents. Subsequent biochemical evaluation of RNAP inhibition demonstrated that the presence of both streptolic acid and tetramic acid subunits was required for activity of this class of antibiotics. In addition, we identified 10,11-dihydroStreptolydigin as a new RNAP-targeting agent, which was assembled with high synthetic efficiency of 15 steps in the longest linear sequence. DihydroStreptolydigin inhibited three representative bacterial RNAPs and displayed in vitro antibacterial activity against S. salivarius . The overall increase in synthetic efficiency combined with substantial antibacterial activity of this fully synthetic antibiotic demonstrates the power of organic synthesis in enabling design and comprehensive in vitro pharmacological evaluation of new chemical agents that target bacterial transcription.

Insights into the roles of exogenous glutamate and proline in improving streptolydigin production of Streptomyces lydicus with metabolomic analysis.[Pubmed:23990132]

J Ind Microbiol Biotechnol. 2013 Nov;40(11):1303-14.

The addition of precursors was one strategy to improve antibiotic production. The exogenous proline and glutamate, as precursors of Streptolydigin, could significantly improve the Streptolydigin production, but their underlying molecular mechanisms remain unknown. Herein, metabolomic analysis was carried out to explore the metabolic responses of Streptomyces lydicus to the additions of proline and glutamine. The significant differences in the quantified 53 metabolites after adding the exogenous proline and glutamate were enunciated by gas chromatography coupled to time-of-flight mass spectrometry. Among them, the levels of some fatty acids (e.g., dodecanoic acid, octadecanoic acid, hexadecanoic acid) were significantly decreased after adding glutamate and proline, indicating that the inhibition of fatty acid synthesis might be benefit for the accumulation of Streptolydigin. Particularly, the dramatic changes of the identified metabolites, which are involved in glycolysis, the tricarboxylic acid cycle, and the amino acid and fatty acid metabolism, revealed that the additions of glutamate and proline possibly caused the metabolic cross-talk in S. lydicus. Additionally, the level of intracellular glutamate dramatically enhanced at 12 h after adding proline, showing that exogenous proline may be firstly convert into glutamate and consequently result in crease of the Streptolydigin production. The high levels of Streptolydigin at 12 and 24 h after adding glutamate unveiled that part glutamate were rapidly used to synthesize the Streptolydigin. Furthermore, there is the significant difference in metabolomic characteristics of S. lydicus after adding glutamate and proline, uncovering that multiple regulatory pathways are involved in responses to the additions of exogenous glutamate and proline. Taken together, exogenous glutamate and proline not only directly provided the precursors of Streptolydigin biosynthesis, but also might alter the metabolic homeostasis of S. lydicus E9 during improving the production of Streptolydigin.

Streptolydigin (Portamycin) is a 3-acetyltetramic acid antibiotic and a potent bacterial RNA polymerase inhibitor with a Ki of 18 μM and a Kd of 15 μM. Streptolydigin inhibits RNA synthesis by binding to RNA polymerase and does not inhibit eukaryotic RNA polymerases. Streptolydigin possess potent antibacterial activity, particularly against anaerobes and some Gram-positive aerobes.

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