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Actin in the merozoite of the malaria parasite, Plasmodium falciparum
S J Field1, J C Pinder, B Clough
1Medical Research Council Muscle and Cell Motility Unit, King's College, London, England.
Abstract:
Merozoites of the human malaria parasite, Plasmodium falciparum, when treated with cytochalasin B, will attach irreversibly to red cells with formation of a vestigial internal (parasitophorous) vacuole, but they are inhibited from moving into the cell. The existence of an actin-based motile mechanism is implied. Immunoblotting, peptide mapping and the DNase inhibition assay have been used to show that the merozoite contains actin. It makes up an estimated 0.3% of the total parasite protein and is partitioned in the ratio of about 1:2 between the cytosolic and particulate protein fractions. In the former it is unpolymerised and in the latter filamentous. Most of the anti-actin-reactive protein in the soluble fraction and about 20% of that in the pellet has an apparent molecular weight of 55,000 and reacts with an anti-ubiquitin antibody; it is thus evidently ubiquitinyl actin, or arthrin, which has so far been detected only in insect flight muscle.
Insights
The malaria parasite Plasmodium falciparum merozoite contains actin, a protein crucial for motility. This discovery suggests a potential new target for antimalarial drugs.
Area of Science:
- Cell Biology
- Parasitology
- Biochemistry
Background:
- Merozoites of Plasmodium falciparum are the infectious stage of the human malaria parasite.
- Cytochalasin B treatment inhibits merozoite invasion into red blood cells, suggesting a motility mechanism.
Purpose of the Study:
- To investigate the presence and characteristics of actin in Plasmodium falciparum merozoites.
- To explore the potential role of actin in merozoite motility and invasion.
Main Methods:
- Immunoblotting
- Peptide mapping
- DNase inhibition assay
- Protein fractionation (cytosolic and particulate)
Main Results:
- Actin was detected in Plasmodium falciparum merozoites, constituting approximately 0.3% of total parasite protein.
- Actin exists in both unpolymerized (cytosolic) and filamentous (particulate) forms.
- A significant portion of the actin-reactive protein is ubiquitinylated (arthrin), a form previously found only in insect muscle.
Conclusions:
- The Plasmodium falciparum merozoite possesses an actin-based motility system, implied by cytochalasin B inhibition.
- The presence of ubiquitinylated actin (arthrin) in the parasite is a novel finding.
- Understanding merozoite actin dynamics could reveal new therapeutic targets for malaria.