| Abstract
| - The glycolipid transfer protein (GLTP) is monomeric in aqueous solutions, and it binds weakly to membraneinterfaces with or without glycolipids. GLTP is a surface-active protein and adsorbs to exert a maximal surface pressurevalue of 19 mN/m. The change in surface pressure following GLTP adsorption decreased linearly with initial surfacepressure. The exclusion pressure for different phospholipids and sphingolipids was between 23 and 31 mN/m, beingclearly highest for the negatively charged dipalmitoyl-phosphatidylserine. This can be explained by electrostatic forceswhen GLTP is positively charged at neutral pH (isoelectric point = 9.0) and by phosphatidylserine being negativelycharged. If GLTP is injected under a palmitoyl-galactosylceramide monolayer above 30 mN/m, the presence of GLTPleads to a decrease in the surface pressure as a function of time. This suggests that GLTP is able to remove glycolipidsfrom the monolayer without penetrating the monolayer. On the other hand, if phospholipid vesicles with or withoutglycolipids are also present in the subphase, no change in the surface pressure takes place. This suggests that GLTPin the presence of curved membranes is not able to transfer from or to planar membranes. We also show that transferof fluorescently labeled galactosylceramide is faster from small highly curved palmitoyl-oleoyl-phosphatidylcholineand dipalmitoyl-phosphatidylcholine bilayer vesicles but not from palmitoyl-sphingomyelin vesicles regardless of thesize.
|
