Identification of a protein unique to the genus Plasmodium that contains a WD40 repeat domain and extensive low-complexity sequence.

Proteins containing WD40 domains play important roles in the formation of multiprotein complexes. Little is known about WD40 proteins in the malaria parasite. This report contains the initial description of a WD40 protein that is unique to the genus Plasmodium and possibly closely related genera. The N-terminal portion of this protein consists of seven WD40 repeats that are highly conserved in all Plasmodium species. Following the N-terminal region is a central region that is conserved within the major Plasmodium clades, such as parasites of great apes, monkeys, rodents, and birds, but partially conserved across all Plasmodium species. This central region contains extensive low-complexity sequence and is predicted to have a disordered structure. Proteins with disordered structure generally function in molecular interactions. The C-terminal region is semi-conserved across all Plasmodium species and has no notable features. This WD40 repeat protein likely functions in some aspect of parasite biology that is unique to Plasmodium and this uniqueness makes the protein a possible target for therapeutic intervention.

Identification of Plasmodium falciparum HSP70-2 as a resident of the Plasmodium export compartment.

The malarial parasite remodels the host erythrocyte following invasion. Well-known examples are adhesive proteins inserted into the host erythrocyte membrane, which function as virulence factors. The modification of the host erythrocyte may be mediated by a specialized domain of the endoplasmic reticulum, or Plasmodium export compartment (PEC). Previously, monoclonal antibodies recognizing the PEC were generated and one of these monoclonal antibodies recognize a 68 kDa parasite protein. In this study, the 68 kDa protein was affinity purified and analyzed by peptide mapping using mass spectrometry. The results demonstrate that the 68 kDa protein is the P. falciparum homolog of the endoplasmic reticulum resident HSP70 called PfHSP70-2. This finding is consistent with the PEC being a domain of the endoplasmic reticulum and suggests a role for PfHSP70-2 in the export of Plasmodium proteins into the host erythrocyte.

Merozoite release from Plasmodium falciparum-infected erythrocytes involves the transfer of DiIC16 from infected cell membrane to Maurer's clefts.

Merozoite release from infected erythrocytes is a complex process, which is still not fully understood. Such process was characterised at ultra-structural level in this work by labelling erythrocyte membrane with a fluorescent lipid probe and subsequent photo-conversion into an electron-dense precipitate. A lipophilic DiIC(16) probe was inserted into the infected erythrocyte surface and the transport of this phospholipid analogue through the erythrocyte membrane was followed up during 48 h of the asexual erythrocyte cycle. The lipid probe was transferred from infected erythrocyte membranes to Maurer's clefts during merozoite release, thereby indicating that these membranes remained inside host cells after parasite release. Fluorescent structures were never observed inside infected erythrocytes preceding merozoite exit and merozoites released from infected erythrocyte were not fluorescent. However, specific precipitated material was localised bordering the parasitophorous vacuole membrane and tubovesicular membranes when labelled non-infected erythrocytes were invaded by merozoites. It was revealed that lipids were interchangeable from one membrane to another, passing from infected erythrocyte membrane to Maurer's clefts inside the erythrocyte ghost, even after merozoite release. Maurer's clefts became photo-converted following merozoite release, suggesting that these structures were in close contact with infected erythrocyte membrane during merozoite exit and possibly played some role in malarial parasite exit from the host cell.