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Published on: March 6, 2013
Synthetic tripeptides as alternate substrates of murein peptide ligase (Mpl)
Mireille Hervé1, Andreja Kovač, Cécile Cardoso
1Univ Paris-Sud, Laboratoire des Enveloppes Bactériennes et Antibiotiques, Institut de Biochimie et Biophysique Moléculaire et Cellulaire, UMR 8619, F-91405 Orsay, France.
Abstract:
Murein peptide ligase (Mpl) is an enzyme found in Gram-negative bacteria. It catalyses the addition of tripeptide L-Ala-γ-D-Glu-meso-diaminopimelate to nucleotide precursor UDP-N-acetylmuramic acid during the recycling of peptidoglycan. Although not essential, this enzyme represents an interesting target for antibacterial compounds through the synthesis of alternate substrates whose incorporation into peptidoglycan might be deleterious for the bacterial cell. Therefore, we have synthesised 10 tripeptides L-Ala-γ-D-Glu-Xaa in which Xaa represents amino acids different from diaminopimelic acid. Tripeptide with Xaa = ε-D-Lys proved to be an excellent substrate of Escherichia coli Mpl in vitro. Tripeptides with Xaa = p-amino- or p-nitro-L-phenylalanine were poor substrates, while tripeptides with Xaa = D- or L-2-aminopimelate, DL-2-aminoheptanoic acid, L-Glu, L-norleucine, L-norvaline, L-2-aminobutyric acid or L-Ala were not substrates at all. Although a good Mpl substrate, the D-Lys-containing tripeptide was devoid of antibacterial activity against E. coli, presumably owing to poor uptake.
Insights
Murein peptide ligase (Mpl) is a target for new antibacterial drugs. Researchers synthesized tripeptides to test Mpl activity, finding one with D-Lys was a good substrate but lacked antibacterial effects.
Area of Science:
- Biochemistry
- Microbiology
- Medicinal Chemistry
Background:
- Murein peptide ligase (Mpl) is crucial for peptidoglycan recycling in Gram-negative bacteria.
- Mpl is a potential target for developing novel antibacterial agents.
- Altering peptidoglycan synthesis via Mpl substrates could inhibit bacterial growth.
Purpose of the Study:
- To synthesize and evaluate novel tripeptide substrates for Mpl.
- To investigate the potential of these substrates as antibacterial agents.
Main Methods:
- Synthesis of ten tripeptides (L-Ala-γ-D-Glu-Xaa) with varying amino acids at the Xaa position.
- In vitro enzymatic assays using purified Escherichia coli Mpl.
- Assessment of antibacterial activity against E. coli.
Main Results:
- A tripeptide containing ε-D-Lys was identified as an excellent Mpl substrate in vitro.
- Tripeptides with p-amino/nitro-L-phenylalanine were poor substrates.
- Several other tripeptides were not Mpl substrates.
- The D-Lys-containing tripeptide showed no antibacterial activity against E. coli, likely due to poor cellular uptake.
Conclusions:
- The study identified an effective in vitro substrate for Mpl, demonstrating the enzyme's substrate specificity.
- Despite effective Mpl interaction, the D-Lys tripeptide's lack of antibacterial activity highlights the importance of cellular permeability for drug efficacy.
- Mpl remains a viable target, but substrate design must consider bacterial uptake mechanisms.
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