An FTIR molecular view of the interaction between the antibiotic peptide Microcin J25 and membranes

DUPUY F., CHEHÍN R. AND MORERO R.D.

Buenos Aires, Argentina

Workshop; International Workshop on Infrared Spectroscopy; 2007

Cátedra de Química Inorgánica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires

Microcin J25 is a 21 aminoacid peptide active against Escherichia coli and Salmonella enteritidis strains. The MccJ25 structure is a nosse-like feature comprising a ring formed by a  N-terminus to Glu8 side-chain amide bond and a C-terminal tail which threads through the ring. Bacterial transcription is inhibited by the binding of the peptide within the RNA polymerase secondary channel, through which the substrates diffuse to the enzyme active site. However, the peptide is capable of inhibit respiratory chain enzymes activity and bind to model membranes also (1). A quantitative study of the partition of MccJ25 and some analogous peptides into membranes was carried out with fluorescence spectroscopy. Considering that MccJ25 is able to interact with biological membranes, Fourier transform infrared spectroscopy (FTIR) was used to study the conformational changes of the membrane as well as the peptide induced by the interaction. This technique is known to be a versatile and powerful tool to investigate changes that occur at different levels of the lipid bilayer, i.e, hydrophobic, interfacial and polar regions (2). In this work, the obtained results shows that MccJ25 could not induce dehydration of the bilayer interfacial region of dipalmitoylphophatydilcholine (DPPC) bilayer. However, a strong perturbation in the core of the bilayer is observed, suggesting that the peptide could insert into the DPPC bilayer. As a consequence, the FTIR spectrum of the peptide structure, evidenced by changes in the Amide I region, show changes. Bands at around 1,625 cm-1, that have been associated with intramolecular interactions (3), such as monomer-monomer contacts, increases in the presence of DPPC liposomes. In the present communication, some evidence that could help to understand the mechanism of action of  MccJ25 on the membrane is provided.