Molecular Dynamics and FTIR studies of Microcin J25 and lipid membranes interaction

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

La Plata

Congreso; XXXVII Reunion Anual de la Sociedad Argentina de Biofisica; 2008

Microcin J25 (MccJ25) is a 21 amino acid antibiotic peptide produced by Escherichia coli strains. Mass spectrometry and nuclear magnetic resonance studies demonstrated that the peptide has a threaded lasso structure and a high hydrophobic character. Bacterial transcription is inhibited by the binding of the peptide within the RNA polymerase secondary channel. However, MccJ25 sensitive strains carrying mutations on RNA polymerase leading to MccJ25 resistance were also isolated, indicating that antibiotic mechanism of action could involve several peptide-target interactions. Indeed, peptide interaction with bacterial membrane leading to permeabilization and inhibition of respiratory chain enzymes activity was demonstrated. MccJ25 is also capable to penetrate PC monolayers and bind to DPPC liposomes. In this work, the interaction of MccJ25 with model membranes was studied by means of both experimental and modeling techniques, i.e Fourier transform infrared spectroscopy (FTIR) and Molecular Dynamics simulations (MD). A mean-field potential based on a continuum electrostatic approximation was used to investigate the importance of thermodynamic and energetic factors in the membrane association of MccJ25. Molecular dynamics trajectories of MccJ25 in an explicit dipalmitoylphosphatidylcholine (DPPC) bilayer were generated to study the details of lipid-protein interactions at the microscopic level. From the initial configuration predicted by the mean-field approach, the peptide conformation remained stable during the 6.5 ns of simulation. During the trajectory, the center of mass of MccJ25 drifted toward the center of the membrane 17,4 ± 0,28 Å along the z axis. The peptide insertion within the membrane has a disordering effect  on lipids directly interacting with it. FTIR spectroscopy also demonstrated that the interaction between MccJ25 and zwiterionic membranes produced a strong perturbation in the hydrophobic region of the bilayer.