Identification of the initial binding sites of αs2-casein f(183–207) and effect on bacterial membranes and cell morphology

The aim of this work was to identify the initial binding sites to the bacterial membranes of the antimicrobial peptide αs2-casein f(183–207) and also to acquire further insight into membrane permeabilization of this peptide. Furthermore, cell morphology was studied by transmission electron microscopy. In all the experiments, bovine LFcin was employed as a comparison. Results showed that initial binding sites of αs2-casein f(183–207) peptide were lipoteichoic acid in Gram-positive bacteria and lipopolysaccharide in Gram-negative. The peptide was able to permeabilize the outer and inner membranes. Moreover, the αs2-casein peptide f(183–207) generated pores in the outer membrane of Gram-negative bacteria and in the cell wall of Gram-positive bacteria. In the Gram-negative bacteria, f(183–207) originated cytoplasm condensation, and in the Gram-positive bacteria the cytoplasmic content leaked into the extracellular medium. Furthermore, the experiments of inner and outer membrane permeabilization performed with LFcin-B showed that this peptide also has the ability to permeabilize both the inner and outer membranes.