Bilayer conformation changes induced by the antibiotic peptide MccJ25 binding: new insights in its mechanism of action

TORRES-BUGEAU, CLARISA MARÍA; DUPUY, FERNANDO; AVILA, CESAR LUIS; MORERO, ROBERTO D; CHEHIN, ROSANA

Cancún, Mexico

Congreso; International Conference & Meetings EMBnet-RIBio 2009; 2009

Microcin J25 is a 21 aminoacid peptide active against Escherichia coli and Salmonella enteritidis strains. The structure of the peptide was elucidated based on mass spectrometry and nuclear magnetic resonance showing a distinctive lasso-structure. Convincing evidence that RNA polymerase is the main target for MccJ25 in E. coli was provided by our laboratory. The peptide activity against cellular and model membranes has also been demonstrated. The interaction and binding of peptides to membranes is of central importance to understand the membrane activity of MccJ25. Since no Trp residue is present on the wild-type MccJ25, the MccJ25 I13W mutant sharing similar structural and microbiological characteristics was obtained to perform fluorescence experiments. In order to explain the peptide activity on membranes, molecular dynamics (MD) simulations of MccJ25 I13W embedded on dipalmitoyl phosphatidylcholine (DPPC) bilayer were carried out. According to our results, the peptide was capable to form stable complex with DPPC membranes and it penetrates into the membrane via its b-hairpin while the terminal rig as well as C-terminal fragment stays adsorbed on the bilayer surface. The maximal depth of insertion was observed for the residue G12 which reach about 5,5 Å from the bilayer center. The membrane response to the peptide insertion was also evidenced from de MD trajectories since the simulations revealed bilayer changes as response to the peptide binding. The average thickness of the lipid bilayer was significantly enhanced in comparison with pure DPPC. Moreover, the order parameter of acyl chains of lipids was increased.  These results suggest that the MccJ25 I13W-membrane binding could form ordered lipid domains. Considering that packing defects in boundaries of different fluidity domains has been proposed, we have tested this possibility by experimental techniques and the obtained results indicates that changes in membrane permeability could explain the antimicrobial effect of the peptide.