Effects of the antibiotic peptide microcin J25 on liposomes: role of acyl chain length and negatively charged phospholipid

This paper reports the effects of microcin J25 (MccJ25) on the microviscosi ty and permeability of phospholipid vesicles of different compositions. The results obtained indicate that MccJ25 interacts with egg L-alpha -phosphat idylcholine (PC) vesicles as demonstrated by peptide intrinsic fluorescence determinations. The interaction depends on the lipid composition of the ve sicles. MccJ25 interaction induces a significant fluidity increase of egg P C vesicles. This effect is time and concentration dependent. Both trimethyl ammonium 1,6-diphenyl-1,3,5-hexatriene and 1,6-diphenyl-1,3,5-hexatriene g ave the same results. The microviscosity of L-a-phosphatidylcholine dipalmi toyl small unilamellar vesicles (SUVs) was affected while that of L-alpha - phosphatidylcholine dimyristoyl vesicles was not, indicating that the effec t was strongly dependent on the chain length of fatty acids. On the other h and, negatively charged L-alpha -phosphatidyl-DL-glycerol (PC) vesicles rem arkably inhibited the peptide effect. Nevertheless vesicles composed of L-a lpha -phosphatidylethanolamine :PG:cardiolipin (7:2:1), a composition resem bling bacterial membrane, were sensitive to the MccJ25 effect. MccJ25 effec tively dissipated the valinomycin-induced membrane potential, but induced o nly a modest leakage (5%) of the trapped Tb+3-dipicolinic acid complex. The se results indicate that the peptides interact and perturb the bilayer of S UVs. The relationships between this effect and bactericidal action remain t o be elucidated. (C) 2000 Elsevier Science B.V. All rights reserved.