Abstract
Lipid rafts, sterol-rich and sphingolipid-rich microdomains on the plasma membrane are important in processes like cell signaling, adhesion, and protein and lipid transport. The virulence of many eukaryotic parasites is related to raft microdomains on the cell membrane. In the malaria parasite Plasmodium falciparum, glycosylphosphatidylinositol-anchored proteins, which are important for invasion and are possible targets for vaccine development, are localized in the raft. However, rafts are poorly understood. We used quick-freezing and freeze-fracture immuno-electron microscopy to examine the localization of monosialotetrahexosylganglioside (GM1) and monosialodihexosylganglioside (GM3), putative raft microdomain components in P. falciparum and infected erythrocytes. This method immobilizes molecules in situ, minimizing artifacts. GM3 was localized in the exoplasmic (EF) and cytoplasmic leaflets (PF) of the parasite and the parasitophorous vacuole (PV) membranes, but solely in the EF of the infected erythrocyte membrane, as in the case for uninfected erythrocytes. Phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) was localized solely in the PF of erythrocyte, parasite, and PV membranes. This is the first time that GM3, the major component of raft microdomains, was found in the PF of a biological membrane. The unique localization of raft microdomains may be due to P. falciparum lipid metabolism and its unique biological processes, like protein transport from the parasite to infected erythrocytes.
Highlights
Lipid rafts, sterol-rich and sphingolipid-rich microdomains on the plasma membrane are important in processes like cell signaling, adhesion, and protein and lipid transport
Our results in this study demonstrated that GM3, a major component of the raft microdomain, was symmetrically localized in both the exoplasmic and cytoplasmic leaflets in the P. falciparum plasma membrane and parasitophorous vacuole (PV) membrane
P. falciparum can be clearly observed in erythrocytes using our freeze-fracture replica method (Fig. 1)
Summary
Nanoscale‐level distribution of GM3 on both the PF and the EF of the P. falciparum plasma membrane and the PV membrane. The gold labeling densities of GM3 of both sides of the PV membrane were much lower than those in the P. falciparum plasma membrane (Fig. 3C) These distribution patterns of GM3 in the parasite plasma membrane and the PV membrane were very similar among any parasites residing in the erythrocyte during the asexual developing stage. It is well known that in mammalian cells PtdIns[4,5]P2 is mainly localized in the plasma membrane and distributed on its PF, but not the EF, Previously, using the freeze-fracture EM method we demonstrated that the highly specific labeling of the probe GST-PLCδ1-PH, which selectively binds to PtdIns[4,5]P2, was detected on the PF, but not the EF, of the human fibroblast plasma m embrane. The localization of GM3 in the plasma membrane of the infected erythrocyte was basically
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