Molecular view by fourier transform infrared spectroscopy of the relationship between lactocin 705 and membranes: speculations on antimicrobial mechanism

Abstract

Lactocin 705 is a bacteriocin whose activity depends upon the complementation of two peptides, termed Lac705alpha and Lac705beta. Neither Lac705alpha nor Lac705beta displayed bacteriocin activity by itself when the growth of sensitive cells was monitored. To obtain molecular insights into the lactocin 705 mechanism of action, Fourier transform infrared spectroscopy was used to investigate the interactions of each peptide (Lac705alpha and Lac705beta) with dipalmitoylphosphatidylcholine liposomal membranes. Both peptides show the ability to interact with the zwitterionic membrane but at different bilayer levels. While Lac705alpha interacts with the interfacial region inducing dehydration, Lac705beta peptide interacts with only the hydrophobic core. This paper presents the first experimental evidence that supports the hypothesis that Lac705alpha and Lac705beta peptides could form a transmembrane oligomer. From the obtained results, a mechanism of action of lactocin 705 on membrane systems is proposed. The component Lac705alpha could induce the dehydration of the bilayer interfacial region, and the Lac705beta peptide could insert in the hydrophobic region of the membrane where the peptide has adequate conditions to achieve the oligomerization.

FIG. 1.

Temperature dependence of the wave number of symmetric methylene stretching ν_s [CH₂] vibration bands of DPPC at pD 7.0 for a pure DPPC SUV liposome (○) and in the presence of Lac705β (•) or Lac705α (▴).

FIG. 2.

FTIR absorption spectra in the amide I′ region of the Lac705β peptide (solid line) and the Lac705β peptide with DPPC liposomes (dashed lines) at 25°C (A) and 50°C (B).