SIZING MEMBRANE PORES IN LIPID VESICLES BY LEAKAGE OF CO-ENCAPSULATEDMARKERS - PORE FORMATION BY MELITTIN

Many toxins and antimicrobial peptides permeabilize membrane vesicles by forming multimeric pores. Determination of the size of such pores i s an important first step for understanding their structure and the me chanism of their self-assembly. We report a simple method for sizing p ores in vesicles based on the differential release of co-encapsulated fluorescently labeled dextran markers of two different sizes. The meth od was tested using the bee venom peptide melittin, which was found to form pores of 25-30 Angstrom diameter in palmitoyloleoylphosphatidylc holine (POPC) vesicles at a lipid-to-peptide ratio of 50. This result is consistent with observations on melittin pore formation in erythroc ytes (Katsu, T., C. Ninomiya, M. Kuroko, H. Kobayashi, T. Hirota, and Y. Fujita. 1988. Action mechanism of amphipathic peptides gramicidin S and melittin on erythrocyte membrane. Biochim. Biophys. Acta, 939:57- 63).