Erythrocyte Binding Protein PfRH5 Polymorphisms Determine Species-Specific Pathways of Plasmodium falciparum Invasion

Abstract

Summary Some human Plasmodium falciparum parasites, but not others, cause malaria in Aotus monkeys. To identify the basis for this variation, we crossed two clones that differ in A. nancymaae virulence and mapped inherited traits of infectivity to erythrocyte invasion by linkage analysis. A major pathway of invasion was linked to polymorphisms in a newly-identified erythrocyte binding protein, PfRH5, found in the apical region of merozoites. Polymorphisms of PfRH5 from the A. nancymaae-virulent parent (GB4) transformed the non-virulent parent (7G8) to a virulent parasite. Conversely, replacements that removed these polymorphisms from PfRH5 converted a virulent progeny clone (LC12) to a non-virulent parasite. A proteolytic fragment of PfRH5 from the infective parasites bound to A. nancymaae erythrocytes. Our results also suggest that PfRH5 is a parasite ligand for human infection, and that amino acid substitutions can cause its binding domain to recognize different human erythrocyte surface receptors.

Transcriptional variation in the malaria parasitePlasmodium falciparum

“…HB3A and HB3B are stocks of the same HB3 clonal parasite line obtained before (HB3A) or after (HB3B) mosquito and chimpanzee passage (Walliker et al 1987), kindly provided by O. Kaneko (Nagasaki University, Japan). The 7G8 parental parasite line and 7G8 subclones identified as 7G8 self-fertilization events MR4, ATCC; Manassas, VA) in a 7G8 3 GB4 genetic cross (Hayton et al 2008) were obtained from MR4 (http://www.mr4.org). Other subclones were generated in this study by limiting dilution.…”

“…Some of these genes (76 of 138) belong to the large hypervariable families var, rif, stevor, and pfmc-2tm (Sup- (Cortés et al 2004). 7G8 subclones were identified as self-fertilization events after passage through mosquito and splectomized chimpanzee (Hayton et al 2008). HB3B was derived from selfcrossing HB3A (Walliker et al 1987).…”

An evolving picture of the interactions between malaria parasites and their host erythrocytes

“…Evidence suggests that the roles of many of these proteins are overlapping: P. falciparum lines can often invade erythrocytes that lack receptors for specific PfEBL or PfRH proteins (because of inherent mutations or enzyme treatment) and, conversely, knockout parasites that do not express individual PfEBL or PfRH proteins have been found to efficiently invade erythrocytes. It thus came as a surprise that focused efforts to knock out the gene encoding an atypical, foreshortened member of the PfRH family, PfRH5, did not succeed in two laboratories [10,11]. While polymorphisms in PfRH5 could be linked to receptor preferences and an ability of a P. falciparum line to also invade Aotus monkey erythrocytes [11], the function of PfRH5 as a parasite ligand and the erythrocyte receptor(s) that it uses for invasion remained unknown.…”

“…It thus came as a surprise that focused efforts to knock out the gene encoding an atypical, foreshortened member of the PfRH family, PfRH5, did not succeed in two laboratories [10,11]. While polymorphisms in PfRH5 could be linked to receptor preferences and an ability of a P. falciparum line to also invade Aotus monkey erythrocytes [11], the function of PfRH5 as a parasite ligand and the erythrocyte receptor(s) that it uses for invasion remained unknown.…”

“…Results show that PfRH5 binds an isoform of basigin on erythrocytes (BSG-S, the Ok blood group antigen, CD147) and that P. falciparum appears to generally require this interaction to efficiently invade human erythrocytes. In contrast to the effects of glycan removal (by neuraminidase) from Aotus erythrocytes on PfRH5 binding and parasite invasion by particular P. falciparum lines [11], removal of all glycans from human basigin does not alter PfRH5 binding [2]. Further, in experiments with multiple P. falciparum clones, Crosnier et al show that the invasion of human erythrocytes is potently inhibited by a soluble pentamerized form of basigin, by anti-basigin monoclonal antibodies, and by reduction of basigin levels on the erythrocyte surface [2].…”