Antimicrobial · Lasso peptide; ribosomally synthesised and post-translationally modified peptide
Microcin J25
Also known as MccJ25
A 21-residue bacterial lasso peptide with a defined RNA polymerase target and transport-dependent antimicrobial activity.
- Length
- 21 amino acids
- Half-life
- Not well characterised
- Mechanism
- Microcin J25 binds within the secondary channel of susceptible bacterial RNA polymerase and inhibits transcription. In susceptible Gram-negative bacteria, uptake depends on proteins including FhuA, the TonB system and SbmA; effects on bacterial respiration have also been reported.
- Studied in
- Purified bacterial RNA polymerase assays, transcription complexes, bacterial uptake mutants and respiratory measurements are used to distinguish target inhibition from transport-dependent susceptibility.
About Microcin J25
Microcin J25 was discovered as a plasmid-encoded antimicrobial peptide produced by Escherichia coli. Its 21-residue mature sequence is GGAGHVPEYFVGIGTPISFYG. A covalent bond between the amino group of Gly1 and the side-chain carboxyl group of Glu8 creates an eight-residue ring. The remaining tail passes through this ring and is sterically trapped, producing the characteristic lasso topology rather than an ordinary head-to-tail cyclic peptide or a disulphide-stabilised fold.
The mcj gene cluster encodes the precursor and machinery responsible for maturation and export. Structural and biochemical studies place microcin J25 in the secondary channel of bacterial RNA polymerase, where it interferes with transcription. Whole-cell susceptibility also depends on access to that intracellular target. Consequently, resistant uptake mutants and purified-enzyme experiments can give different results without contradiction, making transport controls essential when interpreting bacterial activity alongside biochemical target engagement.
Laboratory notes
- Verify the mature lasso topology; the correct sequence and lactam linkage do not by themselves establish correct threading.
- Include uptake-deficient controls when separating FhuA-, TonB- or SbmA-dependent susceptibility from RNA polymerase inhibition.
- Assess stability under the actual assay conditions rather than inferring a quantitative half-life from the constrained structure.
Storage and reconstitution basics: storage guide.
Questions about Microcin J25
What makes microcin J25 a lasso peptide?
Its tail threads through a ring formed by a Gly1–Glu8 isopeptide bond and is held in place by steric constraints.
Is FhuA its intracellular target?
No. FhuA is an outer-membrane uptake receptor in susceptible bacteria; bacterial RNA polymerase is a well-characterised intracellular target.
Why can a bacterium resist microcin J25 despite having susceptible RNA polymerase?
Changes in uptake machinery can prevent sufficient peptide from reaching the enzyme, so whole-cell resistance need not imply target-level resistance.
Is Microcin J25 for human use?
No. It is supplied strictly for in-vitro laboratory research and is not for human or animal consumption.
Related research peptides
All products are sold for laboratory research use only. Not for human consumption, not a medicine, not for diagnosing, treating or preventing any condition.