| Antimicrob Agents Chemother. 2014;58(3):1420-4. |
| Antibiotic streptolydigin requires noncatalytic Mg2+ for binding to RNA polymerase.[Pubmed: 24342645] |
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.
METHODS AND RESULTS:
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.
CONCLUSIONS:
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. |
| J Bacteriol. 2011 Aug;193(16):4214-23. |
| Amino acid precursor supply in the biosynthesis of the RNA polymerase inhibitor streptolydigin by Streptomyces lydicus.[Pubmed: 21665968] |
Biosynthesis of the hybrid polyketide-nonribosomal peptide antibiotic streptolydigin, 3-methylaspartate, is utilized as precursor of the tetramic acid moiety.
METHODS AND RESULTS:
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 ∼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.
CONCLUSIONS:
Overexpression of either slgE3 or slgE1-slgE2 in S. lydicus led to an increase in the yield of streptolydigin. |
| J Am Chem Soc. 2011 Aug 10;133(31):12172-84. |
| Chemical synthesis enables biochemical and antibacterial evaluation of streptolydigin antibiotics.[Pubmed: 21714556] |
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.
CONCLUSIONS:
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. |
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