Attachment of beta 2-glycoprotein I to negatively charged liposomes may prevent the release of daughter vesicles from the parent membrane.

The temperature-induced budding of POPC-cardiolipin-cholesterol, POPC-POPS-cholesterol and POPC-POPG-cholesterol giant lipid vesicles in the presence of beta 2-glycoprotein I (beta 2-GPI) in the outer solution was studied experimentally and theoretically. The observed budding transition of vesicles was continuous which can be explained by taking into account the orientational ordering and direct interactions between oriented lipids. The attachment of positively charged beta 2-GPI to the negatively charged outer surface of POPC-cardiolipin-cholesterol, POPC-POPS-cholesterol and POPC-POPG-cholesterol giant vesicles caused coalescence of the spheroidal membrane bud with the parent vesicle before the bud could detach from the parent vesicle, i.e. vesiculate. Theoretically, the protein-mediated attraction between the membrane of a bud and the parent membrane was described as an interaction between two electric double layers. It was shown that the specific spatial distribution of charge within beta 2-GPI molecules attached to the negatively charged membrane surface may explain the observed attraction between like-charged membrane surfaces.