Small Variant STEVOR Antigen Is Uniquely Located within Maurer's Clefts in Plasmodium falciparum -Infected Red Blood Cells

Abstract

Malaria parasite antigens encoded by multigene families are important factors in virulence and in disease pathology. In Plasmodium falciparum, the virulence factor PfEMP-1 is encoded by the var multigene family and is exposed at the infected erythrocyte surface. PfEMP-1 is clonally variant, allowing the parasite to evade host immunity. The recently identified P. falciparum stevor multigene family and its products also have the potential to be involved in similar important aspects of host-parasite interactions. Here, we show tightly regulated stage-specific transcription of stevor occurring over just a few hours of the asexual parasite life cycle. Only a subset of stevor genes are transcribed in parasite populations maintained in cultures and in single micromanipulated parasites. Antibodies against STEVOR recognize proteins of the expected size (ϳ37 kDa) and localize STEVOR in Maurer's clefts, unique membranous structures located in the cytoplasm of infected erythrocytes. The fact that the timing of stevor expression and the location of STEVOR are clearly distinct from those of other parasite variant antigens suggests that this gene family may have a novel role in P. falciparum biology.To facilitate intraerythrocytic growth and survival, the asexual stage of malaria parasites makes extensive modifications to the parasitized host red blood cell (pRBC) (1). These modifications include the presentation of immunogenic parasite proteins at the surface of the pRBC, exposing the parasite to the effects of host immunity (14,25). Several of these surface proteins, for example, PfEMP-1 in Plasmodium falciparum and SICA antigen in P. knowelsi, induce antibody responses in the infected host which correlate with protection (11, 12). These molecules, encoded by multigene families, have also been shown to be clonally variant, allowing the parasite to evade host immunity. PfEMP-1, encoded by the var multigene family, facilitates the binding of pRBCs to a variety of host receptors on the endothelium, leading to the obstruction of blood vessels and contributing to the pathology and disease severity seen with P. falciparum. PfEMP-1 is thus considered a major virulence factor in P. falciparum infections in humans.Research on malaria multigene families has so far focused on var and rif in P. falciparum and py235 in P. yoelii. However, the Malaria Genome Project has now revealed additional families, including stevor in P. falciparum. Although relatively little is known about stevor, the possibility that its expression product, STEVOR, is involved in virulence, pathology, immunity, and immune evasion warrants more detailed investigation. First reported as 7h8, stevor was initially identified as an expressed sequence detected by a monoclonal antibody (29). There are about 30 to 40 copies of stevor per haploid genome, clustered within 50 kb of the telomeres on all chromosomes (13). Like rif, stevor has short first and longer (ϳ1-kb) second exons. The protein (STEVOR) has a predicted size of 30 to 40 kDa (13) and structurally may be simil...

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

“…We further confirmed these observations in 22-hpi asexual stages before endogenous expression of STEVOR. 16,30,31 At these stages, overexpression of the full copy of STEVOR in the Full-Ty1 line substantially increased the retention rates compared with the control line (78% vs 51.9%, P 5 0), whereas the retention rates of the Trunc-Ty1 line were at the same level as the control line (54.9% vs 51.9%, P 5 .9; Figure 1E-G). Altogether, these results indicate that STEVOR-mediated rigidity of infected erythrocytes is dependent on the C-terminal domain in both asexual and gametocytes stages.…”

A Cluster of Ring Stage–specific Genes Linked to a Locus Implicated in Cytoadherence inPlasmodium falciparumCodes for PEXEL-negative and PEXEL-positive Proteins Exported into the Host Cell

“…In this respect, it is interesting to note that evidence for the presence of different domains in the PVM has recently been provided (Spielmann et al, 2006). Although several transmembrane proteins, such as members of the RIFIN (Kyes et al, 1999), STEVOR (Kaviratne et al, 2002), and PfMC-2TM (Sam-Yellowe et al, 2004) families, are exported in a PEXEL-dependent manner (Marti et al, 2004;Przyborski et al, 2005), these proteins are expressed at the trophozoite stage when the Maurer's clefts have already formed. This would not allow them to be exported during cleft biogenesis.…”

Export of virulence proteins by malaria-infected erythrocytes involves remodeling of host actin cytoskeleton

“…Cells were labeled with antibodies: a-PTP1 (1:500), a-SBP1 (1:500), a-REX1 (1:2000), 32 a-GFP (1:500), a-HA (1:100), a-MAHRP1 (1:100), 33 a-Pf332 (1:500), 34 a-STEVOR (1:500), 35 a-Rif29 (1:200), 36 a-Hsp70-x (1:200), 37 a-PTP2 (1:250). 38 Cells were viewed with a Zeiss Plan-Apochromat 1003/1.4 numeric aperture oil-immersion lens on a Zeiss Axioskop 2 microscope equipped with a PCO SensiCam (12-bit) camera.…”