A novel alternate secretory pathway for the export of Plasmodium proteins into the host erythrocyte

Abstract

The malarial parasite dramatically alters its host cell by exporting and targeting proteins to specific locations within the erythrocyte. Little is known about the mechanisms by which the parasite is able to carry out this extraparasite transport. The fungal metabolite brefeldin A (BFA) has been used to study the secretory pathway in eukaryotes. BFA treatment of infected erythrocytes inhibits protein export and results in the accumulation of exported Plasmodium proteins into a compartment that is at the parasite periphery. Parasite proteins that are normally localized to the erythrocyte membrane, to nonmembrane bound inclusions in the erythrocyte cytoplasm, or to the parasitophorous vacuolar membrane accumulate in this BFA-induced compartment. A single BFA-induced compartment is detected per parasite and the various exported proteins colocalize to this compartment regardless of their final destinations. Parasite membrane proteins do not accumulate in this novel compartment, but accumulate in the endoplasmic reticulum (ER), suggesting that the parasite has two secretory pathways. This alternate secretory pathway is established immediately after merozoite invasion and at least some dense granule proteins also use the alternate pathway. The BFA-induced compartment exhibits properties that are similar to the ER, but it is clearly distinct from the ER. We propose to call this new organelle the secondary ER of apicomplexa. This ER-like organelle is an early, if not the first, step in the export of Plasmodium proteins into the host erythrocyte.

trans Expression of a Plasmodium falciparum Histidine-rich Protein II (HRPII) Reveals Sorting of Soluble Proteins in the Periphery of the Host Erythrocyte and Disrupts Transport to the Malarial Food Vacuole

“…This suggests that unlike transport to apical organelles (32), protein secretion to the red cell is not temporally regulated. This argues against a "secondary ER" that has been proposed to exist as a specialized compartment in Plasmodium dedicated to ring stage export to the erythrocyte (33).…”

“…A biochemical analysis with isolated fv was undertaken to facilitate quantitative estimation of marker association with the vacuoles. These fv preparations have been previously characterized to show that they are enriched in resident proteases but relatively depleted in other cellular proteinases (31,33). They are isolated from trophozoite-stage (24 -36 h) parasites, because this is the time of active hemozoin production.…”

Targeting the Malarial Plastid via the Parasitophorous Vacuole

“…The reasons for the lack of uniform distribution of PTS-GFP accumulated in the ER are not known. A "secondary ER" that accumulates secretory protein in the presence of Bfa has been described in P. falciparum (30). However, the secondary ER is thought to be depleted in PfBiP, suggesting that PTS-GFP does not accumulate there.…”

Developmental-stage-specific triacylglycerol biosynthesis, degradation and trafficking as lipid bodies inPlasmodium falciparum-infected erythrocytes

“…Effect of BFA and trifluoperazine on the formation and trafficking of lipid bodies To gain mechanistic insights into the export of lipid bodies to the cytosol of P. falciparum-infected erythrocytes, we tested the effect of BFA, which has been shown to inhibit the transport and sorting of intracellular molecules through the parasites' endoplasmic reticulum (ER) (Elmendorf and Haldar, 1993;Benting et al, 1994;Wiser et al, 1997;Adisa et al, 2001;Hayashi et al, 2001;Wickham et al, 2001). Tightly synchronized ring stage cultures treated with 5 µg ml -1 BFA for 26 hours or 30 hours were compared with control cultures treated with the carrier solvent, ethanol.…”