title: Microcin J25 has a threaded sidechain-to-backbone ring structure and not a head-to-tail cyclized backbone.
abstract: Microcin J25 is a 21 amino acid bacterial peptide that has potent antibacterial activity against Gram-negative bacteria, resulting from its interaction with RNA polymerase. The peptide was previously proposed to have a head-to-tail cyclized peptide backbone and a tight globular structure (Blond, A., Péduzzi, J., Goulard, C., Chiuchiolo, M. J., Barthélémy, M., Prigent, Y., Salomón, R. A., Farías, R. N., Moreno, F. & Rebuffat, S. Eur. J. Biochem. 1999, 259, 747-755). It exhibits remarkable thermal stability for a peptide of its size lacking disulfide bonds and in part this was previously proposed to derive from its macrocyclic structure. We show here that in fact the peptide does not have a head-to-tail cyclic structure but rather a side chain to backbone cyclization between Glu8 and the N-terminus. This creates an embedded ring that is threaded by the C-terminal tail of the molecule, forming a noose-like feature. The three-dimensional structure deduced from NMR data suggests that slippage of the noose is prevented by two aromatic residues flanking the embedded ring. Unthreading does not occur even when the molecule is enzymatically digested with thermolysin. The new structural interpretation fully accounts for previously reported NMR and biophysical data and is consistent with the remarkable stability of this potent antimicrobial peptide.
authors.affiliation: Institute for Molecular Bioscience, University of Queensland, Brisbane QLD 4072, Australia.
authors.forename: K Johan
authors.initials: KJ
authors.lastname: Rosengren
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Clark
authors.forename: Norelle L
authors.initials: NL
authors.lastname: Daly
authors.forename: Ulf
authors.initials: U
authors.lastname: Göransson
authors.forename: Alun
authors.initials: A
authors.lastname: Jones
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000138:chemical synthesis / Q000737:chemistry; D001430:Bacteriocins / Q000138:chemical synthesis / Q000737:chemistry*; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D000900:Anti-Bacterial Agents; D001430:Bacteriocins; D010456:Peptides, Cyclic; C020411:microcin