Aims: 

Lactobacillus plantarum C11 releases plantaricin A (PlnA), a 26-mer cationic peptide pheromone that also has a membrane-permeabilizing, antibacterial effect. We have previously shown that PlnA may also permeabilize eukaryotic cells, with a potency that differs between cell types. It is generally assumed that cationic antimicrobial peptides exert their effects through electrostatic attraction to negatively charged phospholipids in the membrane. The aim of the present study was to investigate if also negative charge linked to macromolecules at the cell surface may be essential for the permeabilizing effect of PlnA.

Methods: 

We have tested this hypothesis by studying the effects of PlnA on clonal rat anterior pituitary cells (GH4) using patch clamp and microfluorometric techniques.

Results: 

In normal solution, GH4 cells are highly sensitive to PlnA, but the sensitivity was dramatically reduced in solutions with either 10x elevated Ca²⁺ concentration or containing 5 mg/ml poly-D-lysine. Such solutions partly neutralize the negative surface charge of the cells, thus confirming that electrostatic interactions are probably important for the PlnA effects. Trypsination of the cells prior to PlnA exposure also rendered the cells insensitive to the peptide, suggesting that negative charges linked to membrane proteins are crucial for the permeabilizing action of PlnA. Finally, pre-exposure of the cells to a mixture of enzymes that split carbohydrate residues from the protein backbone of proteoglycans also abolished the permeabilizing effect of PlnA.

Conclusion: 

Electrical attraction between PlnA and glycosylated membrane proteins is probably an essential first step before PlnA can interact with membrane phospholipids.