Plasmodium falciparum Erythrocyte Membrane Protein 3 (PfEMP3) Destabilizes Erythrocyte Membrane Skeleton

Abstract

Plasmodium falciparum erythrocyte membrane protein 3 (PfEMP3) is a parasite-derived protein that appears on the cytoplasmic surface of the host cell membrane in the later stages of the parasite's development where it associates with membrane skeleton. We have recently demonstrated that a 60-residue fragment (FIa1, residues 38 -97) of PfEMP3 bound to spectrin. Here we show that this polypeptide binds specifically to a site near the C terminus of ␣-spectrin at the point that spectrin attaches to actin and protein 4.1R in forming the junctions of the membrane skeletal network. We further show that this polypeptide disrupts formation of the ternary spectrin-actin-4.1R complex in solution. Importantly, when incorporated into the cell, the PfEMP3 fragment causes extensive reduction in shear resistance of the cell. We conjecture that the loss of mechanical cohesion of the membrane may facilitate the exit of the mature merozoites from the cell.The intraerythrocytic form of Plasmodium falciparum, the agent of the most severe type of human malaria, exports many (according to a proteomic estimate, up to 400) proteins into the host cell in the course of its growth and development (1-3). Certain of these proteins are known to associate with the host cell membrane skeleton and thereby modify its structure and properties. Among the changes that have been reported are an altered morphology, an increased membrane rigidity, and an enhanced propensity to adhere to the vascular endothelium (4). Several such proteins that bind to the red cell membrane skeleton have so far been characterized. When the parasite first invades red cells, it deposits RESA (the ring parasite-infected erythrocyte surface antigen) at the membrane skeleton of the newly invaded cell where it binds to spectrin and protects against thermal damage (5-7). As the intracellular parasite further matures, it traffics further proteins to the skeleton. P. falciparum erythrocyte membrane protein 1, or PfEMP1, 2 is inserted into the red cell membrane and its extracellular domain adheres to receptors on endothelial cells (8). PfEMP1 clusters on the red cell surface at dimpled areas called knobs by binding of its intracellular domain to the parasite-encoded protein KAHRP (knob-associated histidine-rich protein) from which knobs are formed (9) and to spectrin and actin (10). KAHRP itself is stabilized at the membrane by interactions with the fourth repeat of spectrin ␣-chain (11). MESA (the mature parasite-infected erythrocyte surface antigen) binds to the 30-kDa domain of protein 4.1R and displaces the host protein p55 (12, 13). Its role in parasite biology is still uncertain, but interference with MESA binding is lethal to the parasite (14). The P. falciparum erythrocyte membrane protein 3 (PfEMP3), with which we are concerned here, is a large protein of 315 kDa that is expressed from the late ring stage onward and is exported via the Maurer's clefts, vesicular structures of parasite origin, into the cytoplasm of the red cell, where it associates with membrane skeleton. H...

Plasmodium falciparum STEVOR proteins impact erythrocyte mechanical properties

“…7 Moreover, other exported proteins have been reported to contribute to the overall rigidity of the infected erythrocyte, such as KAHRP or PfEMP3, which both interact with the erythrocyte membrane skeleton. 4,26,27 However, the strong increase in rigidity during the life cycle of the KAHRP-and PfEMP3-deficient B3 clone reported here suggests that these proteins play a secondary role in the rigidification of the infected erythrocyte.…”

Plasmodium falciparum STEVOR phosphorylation regulates host erythrocyte deformability enabling malaria parasite transmission

“…9 These proteins associate with the erythrocyte membrane skeleton where they are proposed to induce cross-linking of cytoskeletal proteins. [10][11][12][13] In sexual stages, the switch in deformability is linked to expression and localization of STEVOR (SubTElomeric Variable Open Reading frame) proteins at the erythrocyte membrane. 6 The stevor multicopy gene family is 1 of the 3 major families of variant genes in P falciparum, and comprises 35 genes that are clonally expressed.…”

A switch in infected erythrocyte deformability at the maturation and blood circulation of Plasmodium falciparum transmission stages

“…A possible interaction with erythrocyte cytoskeletal proteins may induce spectrin cross-linking, as proposed for the plasmodial proteins KAHRP and PfEMP3 exported in asexual stages. [34][35][36] Deassociation from the erythrocyte membrane in mature stages may result from proteolytic cleavage or conformational changes on posttranslational modifications. Such events are probably responsible for the failure of our antibodies to detect STEVOR association with the erythrocyte membrane in mature GIEs, although this was observed using a different set of antibodies raised to small peptides.…”