Methionine transport in the malaria parasite Plasmodium falciparum

Abstract

The intraerythrocytic malaria parasite, Plasmodium falciparum, derives amino acids from the digestion of host cell haemoglobin. However, it also takes up amino acids from the extracellular medium. Isoleucine is absent from adult human haemoglobin and an exogenous source of isoleucine is essential for parasite growth. An extracellular source of methionine is also important for the normal growth of at least some parasite strains. In this study we have characterised the uptake of methionine by P. falciparum-infected human erythrocytes, and by parasites functionally isolated from their host cells by saponin-permeabilization of the erythrocyte membrane. Infected erythrocytes take up methionine much faster than uninfected erythrocytes, with the increase attributable to the flux of this amino acid via the New Permeability Pathways induced by the parasite in the erythrocyte membrane. Having entered the infected cell, methionine is taken up by the intracellular parasite via a saturable, temperature-dependent process that is independent of ATP, Na(+) and H(+). Substrate competition studies, and comparison of the transport of methionine with that of isoleucine and leucine, yielded results consistent with the hypothesis that the parasite has at its surface one or more transporters which mediate the flux into and out of the parasite of a broad range of neutral amino acids. These transporters function most efficiently when exchanging one neutral amino acid for another, thus providing a mechanism whereby the parasite is able to import important exogenous amino acids in exchange for surplus neutral amino acids liberated from the digestion of host cell haemoglobin.

Transport proteins of parasitic protists and their role in nutrient salvage

“…The single predicted AAAP in P. falciparum (TransportDB; Figure 2) reflects the parasite's ability to internalize and digest haemoglobin from the host (Wunderlich et al, 2012), a valuable source of amino acids. However, haemoglobin is absent in isoleucine and low in methionine, which likely explains why the parasite imports these amino acids (Cobbold et al, 2011), although the transporter(s) responsible has not yet been identified.…”

Identification of inhibitors that dually target the new permeability pathway and dihydroorotate dehydrogenase in the blood stage of Plasmodium falciparum

“…In addition, parasites require purine precursors and pantothenate from the plasma56. While many of these metabolites can be transported across the erythrocyte plasma membrane and be subsequently utilized by intracellular parasite stages, others are either not transported or transported at a rate that is insufficient to sustain rapid parasite growth578910. The malaria parasite overcomes this problem by remodelling nutrient transport pathways in the erythrocyte membrane through the expression of the new permeability pathways (NPPs), which allow entry of a wide range of nutrients required for parasite growth, allowing faster permeation of smaller, anionic and non-polar solutes1112.…”

Chemical activation of a high-affinity glutamate transporter in human erythrocytes and its implications for malaria-parasite–induced glutamate uptake

“…The infected erythrocytes were cultivated either under "shaking" conditions, in RPMI 1640 medium (PAA E15-840; supplemented with 0.5% wt/vol AlbuMax II (Invitrogen), 25mM HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid), 20mM glucose, 24 g/mL gentamicin and 200M hypoxanthine) at a hematocrit of 2%, 31 or under "static" conditions in the same medium supplemented with 10% vol/vol human serum (from the Marburg Blood Bank). 32 Experiments were carried out with trophozoitestage P falciparum-infected erythrocytes (30-35 hours after invasion) enriched to 85%-95% parasitemia either using a VarioMACS separation unit (Miltenyi Biotec) as described elsewhere, 6 or using the plasmagel method. 33 …”

“…The estimation of the amount of radiolabel trapped in the extracellular space of the cell pellet, and the calculation of the distribution ratio, was performed as described elsewhere. 6 …”

“…[1][2][3][4][5] The increased permeability facilitates the uptake into the infected cell of several key nutrients, [6][7][8] as well as the uptake of various antiparasitic agents. [8][9][10][11][12] Parasiteinduced pathways also mediate both the efflux of metabolic wastes, 6,13 and a marked change in the ionic composition of the host cell cytosol. 4,14 The question of the number and origin of the pathways underpinning the parasite-induced increase in host erythrocyte permeability has been a vexed one.…”