Abstract
Invasion of erythrocytes by Plasmodium falciparum involves a complex cascade of protein-protein interactions between parasite ligands and host receptors. The reticulocyte binding-like homologue (PfRh) protein family is involved in binding to and initiating entry of the invasive merozoite into erythrocytes. An important member of this family is PfRh5. Using ion-exchange chromatography, immunoprecipitation and mass spectroscopy, we have identified a novel cysteine-rich protein we have called P. falciparum Rh5 interacting protein (PfRipr) (PFC1045c), which forms a complex with PfRh5 in merozoites. Mature PfRipr has a molecular weight of 123 kDa with 10 epidermal growth factor-like domains and 87 cysteine residues distributed along the protein. In mature schizont stages this protein is processed into two polypeptides that associate and form a complex with PfRh5. The PfRipr protein localises to the apical end of the merozoites in micronemes whilst PfRh5 is contained within rhoptries and both are released during invasion when they form a complex that is shed into the culture supernatant. Antibodies to PfRipr1 potently inhibit merozoite attachment and invasion into human red blood cells consistent with this complex playing an essential role in this process.
Highlights
Malaria is caused by parasites from the genus Plasmodium, of which Plasmodium falciparum is associated with the most severe form of the disease in humans
A family of proteins called P. falciparum reticulocyte binding-like homologue (PfRh) proteins are important for recognition of the red blood cell and activation of the invasion process
We have identified a novel cysteine-rich protein we have called P. falciparum Rh5 interacting protein (PfRipr), which forms a complex with PfRh5 in merozoites
Summary
Malaria is caused by parasites from the genus Plasmodium, of which Plasmodium falciparum is associated with the most severe form of the disease in humans. Sporozoite forms of these parasites are injected into humans during mosquito feeding and they migrate to the liver where they invade hepatocytes and develop into merozoites, which are released to invade erythrocytes in the blood stream. PfRh1, PfRh2b, PfRh2a, PfRh4 and PfRh5 bind to erythrocytes and antibodies to them can inhibit merozoite invasion showing they play a role in this process [11,13, 18,19,20,22,23,24]
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