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Membrane knobs of unfixed Plasmodium falciparum infected erythrocytes: new findings as revealed by atomic force
M Aikawa1, K Kamanura, S Shiraishi
1Research Institute of Medical Sciences, Tokai University, Isehara, Japan.
Abstract:
Cerebral malaria, a severe complication of malaria, is caused by the obstruction of cerebral microvessels by Plasmodium falciparum-infected erythrocytes. Such cells adhere to endothelial cells by means of "knobs" induced on the red cell membrane by the parasites. When atomic force microscopy was used to investigate the structure of the knobs of unfixed infected red cells, each knob was found to consist of two distinct subunits, knob components that have never been seen in chemically fixed knobs examined by conventional transmission electron microscopy. Surface potential spectroscopy revealed that the knobs have a positive charge (+20 mV), whereas the remainder of the red cell plasma membrane is negatively charged. Since endothelial plasma membranes have a negative charge, the charge difference between knobs and endothelium may play a significant role in cytoadherence between the two cell types. The subunit structure of the knobs may be a steric necessity to align adherence molecules so that they can exert their effect. This study shows that the atomic force microscope has great potential for examination of cells in their native state; in combination with surface potential spectroscopy, it may uncover fundamental processes and mechanisms in cell function.
Insights
Atomic force microscopy revealed unique knob structures on malaria-infected red blood cells. These knobs have a positive charge, potentially explaining their adherence to blood vessel walls.
Area of Science:
- Cell Biology
- Parasitology
- Biophysics
Background:
- Cerebral malaria is a severe complication of malaria.
- Obstruction of cerebral microvessels by Plasmodium falciparum-infected erythrocytes causes cerebral malaria.
- Parasite-induced knobs on red blood cells mediate adherence to endothelial cells.
Purpose of the Study:
- To investigate the structure of knobs on unfixed, malaria-infected red blood cells using atomic force microscopy.
- To analyze the surface charge of these knobs and compare it to the surrounding red blood cell membrane and endothelial cells.
- To understand the role of knob structure and charge in cytoadherence.
Main Methods:
- Atomic force microscopy (AFM) was used to examine unfixed, infected red blood cells.
- Surface potential spectroscopy was employed to measure the electrical charge of the knobs.
- Comparison of findings with conventional transmission electron microscopy of fixed cells.
Main Results:
- AFM revealed knobs composed of two distinct subunits, not observed in fixed cells.
- Knobs exhibited a positive surface charge (+20 mV), while the red blood cell membrane was negatively charged.
- The positive charge of knobs and negative charge of endothelium suggest a role in cytoadherence.
Conclusions:
- Atomic force microscopy allows examination of cells in their native state.
- The subunit structure of knobs may be crucial for aligning adherence molecules.
- Surface potential spectroscopy combined with AFM can reveal fundamental mechanisms in cell function, particularly cytoadherence in cerebral malaria.