A MccJ25 tyrosil radical is involved in the respiratory chain inhibition by the antimicrobial peptide

M.C. CHALON, N. WILKE, M.V. NIKLISON CHIROU, L. CORTEZ, A. BELLOMIO, R.D. MORERO, R. CHEHÍN, R.N. FARÍAS Y P.A. VINCENT.

Congreso; XXXVIII Reunión anual de la Sociedad Argentina de Biofísica; 2011

MccJ25 is an antimicrobial peptide that targets both, the transcription process and the bacterialmembrane respiratory chain, inhibiting cell oxygen consumption. This last effect is mediated byan increase in superoxide production by the respiratory processes. Tyr9 of MccJ25 wasdemonstrated as essential for the action on the respiratory chain. Redox-active tyrosineresidues play important roles in catalysis in several enzymes, including ribonucleotidereductase, prostaglandin H synthase, and Photosystem II [1]. Here we investigated the tyrosilradical formation in MccJ25 using Electronic Paramagnetic Resonance (EPR) and Fouriertransform infrared spectroscopy (2D-FTIR). The tyrosil radical was detected by EPR whenMccJ25 was incubated in the presence of H2O2 and DBNBS (trapping of the tyrosil radical).Moreover, FTIR experiments showed an increment of tyrosil radical band located at 1,478 cm-1in the spectrum. Moreover the redox potential of microcina J25 was determinated by cyclicvoltammetry techniques and an irreversible oxidation at about 970 mV vs calomel electrode wasdetected, a value corresponding to tyrosine oxidation. On other hand, MccJ25 was unable toinhibited respiratory chain enzymes activities when the experiments were performed withmembranes obtained from E. coli deficient in cytochrome bd and quinones productionpathways. These results confirm the presence of a tyrosil radical in MccJ25 molecule andsuggest that it could be formed by oxidation in the respiratory chain. Moreover, we proposedthat cytochrome bd and quinores are essential for the MccJ25 effect on respiratory chain.[1] Vassiliev, I. R., Offenbacher, A. R., Barry, B. A.,J. Phys. Chem. B., 2005,109:23077-23085.