Molecular dynamics and FTIR studies of Microcin J25 and lipid membrana interaction

TORRES BUGEAU, C.; DUPUY, F.; AVILA, C.L.; MORERO, R.D.; CHEHÍN, R

La Plata- Argentina

Congreso; XXXVII Reunión Anual de la Sociedad Argentina de Biofísica.; 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 membrames was studied by means of both experimental and modeling techniques, i.e Fourier transform infrared spectroscopy (FTIR) and Molecular Dynamics simulations (MD). In order to detect the most probable peptide-membrane orientation, electrostatic free energy of the system as a function of protein orientation was explored and the orientation in which the system reachs the minimal ÄGel was determinated. MD simulations of MccJ25 in interaction with a hydrated dipalmitoylphosphatidylcholine (DPPC) bilayer was employed. The peptide conformation remained stable during the 6.5 ns simulation. The results revealed that the peptide can reach the hydrophobic region of the membrane 7 A° depth regarding the membrane plane. The peptide insertion within the membrane has a disordering effect (in good agreement with experimental data) and a fluidifying effect on lipids directly interacting with it, and an ordering effect on those not directly interacting. FTIR spectroscopy also demonstrated that the interaction between MccJ25 and zwiterionic membranes produced a strong perturbation in the hydrophobic region of the bilayer.