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Mechanism of action of purpuromycin
P Landini1, E Corti, B P Goldstein
1Marion Merrel Dow Research Institute, Lepetit Research Center, Varese, Italy.
Abstract:
Purpuromycin, an antibiotic active against both fungi and bacteria, shows different modes of action against these two kinds of micro-organisms; in Candida albicans it inhibits RNA synthesis, whereas in Bacillus subtilis protein synthesis is primarily affected, with DNA and RNA synthesis blocked at higher concentrations of the drug. In bacterial cell-free protein-synthesis systems, purpuromycin did not inhibit synthesis from endogenous mRNA (elongation of peptides initiated within the intact cell) but inhibited MS2-phase RNA-dependent protein synthesis (which requires initiation) by 50% at 0.1 mg/l. Poly(U)-directed polyphenylalanine synthesis was 50% inhibited by 20 mg of purpuromycin/l when added to a complete system; however, when purpuromycin was preincubated with ribosomes dissociated into 30 S and 50 S subunits, the concentration for 50% inhibition fell to 0.1 mg/l. By contrast, in a C. albicans cell-free system poly(U)-directed polyphenylalanine synthesis was partially inhibited only at 200 mg/l. Purpuromycin also inhibited polynucleotide synthesis in vitro in reactions using Escherichia coli or wheat-germ RNA polymerases or E. coli DNA polymerase I. We suggest that in bacteria the primary target of purpuromycin is on ribosomes and that its action precedes the elongation step of protein synthesis. The effect on nucleic acid synthesis in both fungi and bacteria may be due to interaction of purpuromycin with DNA.
Insights
Purpuromycin, an antibiotic, targets bacterial protein synthesis initiation and fungal RNA synthesis. Its primary action in bacteria involves ribosomes, potentially affecting DNA interactions.
Area of Science:
- Microbiology
- Molecular Biology
- Pharmacology
Background:
- Purpuromycin exhibits antimicrobial activity against both fungi and bacteria.
- The antibiotic displays distinct mechanisms of action depending on the microorganism.
- Understanding these mechanisms is crucial for developing targeted antimicrobial therapies.
Purpose of the Study:
- To elucidate the differential modes of action of purpuromycin in fungi (Candida albicans) and bacteria (Bacillus subtilis).
- To investigate the specific molecular targets of purpuromycin in bacterial protein synthesis.
- To examine the effects of purpuromycin on nucleic acid synthesis in vitro.
Main Methods:
- Utilized bacterial and fungal cell-free systems to assess protein and nucleic acid synthesis.
- Investigated the inhibition of protein synthesis using endogenous mRNA and MS2-phase RNA.
- Examined the effect of purpuromycin on polyphenylalanine synthesis in the presence and absence of pre-incubated ribosomal subunits.
- Assessed the inhibition of polynucleotide synthesis using bacterial and plant RNA and DNA polymerases.
Main Results:
- In Candida albicans, purpuromycin primarily inhibits RNA synthesis.
- In Bacillus subtilis, purpuromycin primarily affects protein synthesis initiation, with secondary effects on DNA and RNA synthesis at higher concentrations.
- Purpuromycin significantly inhibits bacterial protein synthesis initiation at low concentrations (0.1 mg/l), with pre-incubation with ribosomal subunits enhancing this effect.
- Higher concentrations (200 mg/l) were required to partially inhibit protein synthesis in a fungal cell-free system.
- Purpuromycin demonstrated inhibitory effects on in vitro polynucleotide synthesis mediated by various RNA and DNA polymerases.
Conclusions:
- The primary target of purpuromycin in bacteria is the ribosome, specifically inhibiting the initiation step of protein synthesis.
- The observed effects on nucleic acid synthesis in both fungi and bacteria may stem from purpuromycin's interaction with DNA.
- Purpuromycin possesses distinct antimicrobial mechanisms, offering potential for selective therapeutic applications.