Evidences of a cooperative partition of the MccJ25 peptide into membranes

DUPUY, F; CHEHÍN, RN; MORERO, R.D

Montevideo- Uruguay

Congreso; . IV International conference of Biological Physics; 2007

Sociedad Argentina de Biofísica

Microcin J25 is a 21 aminoacid peptide active against Escherichia coli and Salmonella enteritidis strains. The structure of MccJ25 was elucidated based on mass spectrometry and nuclear magnetic resonance showing a distinctive lasso-structure with high hydrophobic character. Our laboratory provided convincing evidence that RNA polymerase is the main target for MccJ25 action in E. coli. However, peptide activity against cellular and model membranes has also been shown. In a previous report, the interaction of tryptophan containing microcin mutants, MccJ25 I13W and MccJ25 V6W with model membranes was studied by means of fluorescence quenching. In this work, a quantitative study of the partition of the peptides into membranes was carried out with fluorescence spectroscopy. When liposomes made of dipalmitoylphosphatidylcholine are added up to 200:1 phospholipid:peptide ratio, a blue shift of the tryptophan fluorescence spectrum and a sigmoidal enhancement of the intensity are observed, suggesting a cooperative partitions of the peptide into the hydrophobic environment. Both the partition coefficient and the Hill coefficient were calculated by fitting the data to a modified form of the general hyperbolic partition equation, that takes account the sigmoidal; behavior observed, using non-linear least-squares analysis (Sigma Plot). To obtain molecular insights of the peptide partition into membranes, Fourier transform infrared spectroscopy was used. The peptide spectrum in aqueous solution shows two principal shoulders centered at 1645 cm-1 and 1625 cm-1 respectively. The later band is shifted 2 cm-1 to higher wavenumber in the presence of DPPC liposomes, indicating changes in the structure of the peptides upon lipid binding that could be driving the cooperativism of the partition. Significant changes were also observed in the onset of the vas [CH2] and vs [CH2] wavenumbers. However, any detectable effect on the interfacial region of the phospholipids could be seen.