Ca2+-induced fusion of sulfatide-containing phosphatidylethanolamine small unilamellar vesicles

Abstract

The fusogenic properties of sulfatide-containing 1,2-dioleoyl-3sn -phosphatidylethanolamine (DOPE) small unilamellar vesicles (SUVs) in the presence of CaCl 2 were studied by mixing membrane lipids based on an assay of fluorescence resonance energy transfer (FRET). Fusion of the vesicles was also confirmed by mixing aqueous contents with the Tb/dipicolinate (DPA) assay. The half-times of lipid mixing revealed that the fusion rate decreased with increasing molar concentration of sulfatide. This inhibitory effect was more obvious at sulfatide concentrations higher than 30 mol%, where hydration at the membrane surface reached its maximum and the fusion was no longer pH-sensitive in the range of pH 6.0 -9.0. Similar inhibitory effect was also observed in Ca 2 ϩ -induced fusion of DOPE/ganglioside GM 1 vesicles but at a lower concentration of the glycosphingolipid (20 mol%). In contrast, increasing the concentration of phosphatidylserine (PS) in DOPE/PS SUVs resulted in an increase in the rate of Ca 2 ؉ -induced lipid mixing and the pH sensitivity of this system was not affected. These results are consistent with an increasing steric hindrance to membrane fusion at higher molar concentration and larger headgroup size of the glycosphingolipids. Interestingly, the pH sensitivity of the sulfatide-containing liposomes was retained when they were allowed to fuse with synaptosomes in the absence of Ca 2 ؉ by a mechanism involving protein mediation. -Wu, X., and Q-T. Li. Ca 2 ؉ -induced fusion of sulfatide-containing phosphatidylethanolamine small unilamellar vesicles.

Sphingolipids (Galactosylceramide and Sulfatide) in Lamellar−Hexagonal Phospholipid Phase Transitions and in Membrane Fusion

“…This inhibition was found to have two components, namely, inhibition of enzyme activity and stabilization of lamellar phases by gangliosides, resulting in inhibition of the putative nonlamellar fusion intermediates. Various sphingolipids have also been independently assessed as fusion suppressors. , Similar to the case for the inhibition of myelin basic protein-induced vesicle fusion, cerebrosides (Figure ) reproduce the effect of gangliosides, only at higher concentrations, as expected from the results discussed above. The extended fusion lag time in the 20% cerebroside sample (Figure C) is consistent with the idea that formation of the fusion pores is being hindered beyond mere enzyme inhibition (Figure A), the latter being directly responsible for the (smaller) change in vesicle aggregation (Figure B).…”

Identification of the Lipid Antigens Recognized by rHIgM22, a Remyelination-Promoting Antibody

“…Sulfatide topology, distribution and dynamics in phospholipid bilayers, however, is also affected by the presence of proteins that are supposed to be physiologically relevant partners of sulfatide, such as myelin basic protein (MBP) [67,68]. Furthermore, several studies highlighted a role of external factors, like the presence of soluble sulfatide binding proteins [69], pH [70,71], and the presence of cations [72,73] in the dynamics and distribution of sulfatide in phospholipid bilayers. This suggests that the binding of rHIgM22 to sulfatide in oligodendrocytes and in myelin could be affected by a plethora of factors, and could actually be different than the one observed in the in vitro experiments.…”