title: Redox-active tyrosine residue in the microcin J25 molecule.
abstract: Microcin J25 (MccJ25) is a 21 amino acid lasso-peptide antibiotic produced by Escherichia coli and composed of an 8-residues ring and a terminal 'tail' passing through the ring. We have previously reported two cellular targets for this antibiotic, bacterial RNA polymerase and the membrane respiratory chain, and shown that Tyr9 is essential for the effect on the membrane respiratory chain which leads to superoxide overproduction. In the present paper we investigated the redox behavior of MccJ25 and the mutant MccJ25 (Y9F). Cyclic voltammetry measurements showed irreversible oxidation of both Tyr9 and Tyr20 in MccJ25, but infrared spectroscopy studies demonstrated that only Tyr9 could be deprotonated upon chemical oxidation in solution. Formation of a long-lived tyrosyl radical in the native MccJ25 oxidized by H₂O₂ was demonstrated by Electron Paramagnetic Resonance Spectroscopy; this radical was not detected when the reaction was carried out with the MccJ25 (Y9F) mutant. These results show that the essential Tyr9, but not Tyr20, can be easily oxidized and form a tyrosyl radical.
authors.affiliation: Departamento de Bioquímica de la Nutrición, Instituto Superior de Investigaciones Biológicas (Consejo Nacional de Investigaciones Científicas y Técnicas-Universidad Nacional de Tucumán) and Instituto de Química Biológica Dr Bernabé Bloj, Chacabuco 461, 4000 San Miguel de Tucumán, Tucumán, Argentina.
authors.forename: Miriam C
authors.initials: MC
authors.lastname: Chalón
authors.forename: Natalia
authors.initials: N
authors.lastname: Wilke
authors.forename: Jens
authors.initials: J
authors.lastname: Pedersen
authors.forename: Stefano
authors.initials: S
authors.lastname: Rufini
authors.forename: Roberto D
authors.initials: RD
authors.lastname: Morero
authors.forename: Leonardo
authors.initials: L
authors.lastname: Cortez
authors.forename: Rosana N
authors.initials: RN
authors.lastname: Chehín
authors.forename: Ricardo N
authors.initials: RN
authors.lastname: Farias
authors.forename: Paula A
authors.initials: PA
authors.lastname: Vincent
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D001430:Bacteriocins / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005292:Ferricyanides; D006861:Hydrogen Peroxide / Q000737:chemistry; D010084:Oxidation-Reduction; D013055:Spectrophotometry, Infrared; D014443:Tyrosine / Q000737:chemistry*; D014732:Vibration
chemical_list: D000900:Anti-Bacterial Agents; D001430:Bacteriocins; D005292:Ferricyanides; C007931:hexacyanoferrate III; C020411:microcin; D014443:Tyrosine; D006861:Hydrogen Peroxide