Protein Targeting to the Parasitophorous Vacuole Membrane of Plasmodium falciparum

Abstract

Red blood cell (RBC) invasion and parasitophorous vacuole (PV) formation by Plasmodium falciparum are critical for the development and pathogenesis of malaria, a continuing global health problem. Expansion of the PV membrane (PVM) during growth is orchestrated by the parasite. This is particularly important in mature RBCs, which lack internal organelles and no longer actively synthesize membranes. Pfs16, a 16-kDa integral PVM protein expressed by gametocytes, was chosen as a model for studying the trafficking of material from the parasite across the PV space to the PVM. The locations of Pfs16-green fluorescent protein (GFP) reporter proteins containing distinct regions of Pfs16 were tracked from RBC invasion to emergence. Inclusion of the 53 C-terminal amino acids (aa) of Pfs16 to a GFP reporter construct already containing the N-terminal secretory signal sequence was sufficient for targeting to and retention on the PVM. An amino acid motif identified in this region was also found in seven other known PVM proteins. Removal of the 11 C-terminal aa did not affect PVM targeting, but membrane retention was decreased. Additionally, during emergence from the PVM and RBC, native Pfs16 and the full-length Pfs16-GFP reporter protein were found to concentrate on the ends of the gametocyte. Capping was not observed in constructs lacking the amino acids between the N-terminal secretory signal sequence and the transmembrane domain, suggesting that this region, which is not required for PVM targeting, is involved in capping. This is the first report to define the amino acid domains required for targeting to the P. falciparum PVM.

Changes in the transcriptome of the malaria parasite Plasmodium falciparumduring the initial phase of transmission from the human to the mosquito

“…The gene pfs16 was selected as an internal control, because it is known to be highly expressed in gametocytes throughout development, while it is absent in the gametes [7,27,28]. Furthermore two sexual stage-specific genes, actin II and pfs25 , served as external controls.…”

“…Pfs16 is a transmembrane protein of the gametocyte PVM [12,27,48,49]. After the PVM has ruptured during the egress of the activated gametocyte from the host cell, Pfs16 is not detectable any longer in the sexual stage parasites [7] (see below), explaining the decrease of transcript following activation.…”

The PHIST protein GEXP02 targets the host cytoskeleton during sexual development of Plasmodium falciparum

“…Similar to GEXP02-tdTomato, GEXP02-HA localises to the GIE periphery in all stages as shown by immunofluorescence assays (IFA) with a signal also observed within the parasite. We used antibodies against Pfs16, a gametocyte-specific protein localising to the parasitophorous vacuolar membrane (PVM; Eksi & Williamson, 2011), to confirm that GEXP02-HA was exported into the RBC in sexual stages (Figure 1c).…”

Human Erythrocyte Remodelling by Plasmodium falciparum

“…These data indicate that the parasite's translocation machinery is able to recognize both the classical and recessed signal peptides, and in the absence of any additional sorting information, proteins are transported into the parasitophorous vacuole. However, a 34 amino acid sequence in the C-terminal region of eight studied PVM proteins was proposed to be the parasitophorous targeting motif (Eksi & Williamson, 2011). On the other hand, additional information is required for most proteins, which are exported beyond the confines of the parasite across the parasitophorous vacuole to the erythrocyte cytosol and surface.…”