Plasmodium falciparum Rosetting Epitopes Converge in the SD3-Loop of PfEMP1-DBL1α

Davide Angeletti,María Del Pilar Quintana,Susanna M Bächle,Alan Sawyer,Letusa Albrecht,Tahmina Akhter,Kirsten Moll,Karin Blomqvist,Adnane Achour,Mats Wahlgren,Tatyana Sandalova

doi:10.1371/journal.pone.0050758

Davide Angeletti, María Del Pilar Quintana + Show 9 more

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https://doi.org/10.1371/journal.pone.0050758

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Abstract

The ability of Plasmodium falciparum parasitized RBC (pRBC) to form rosettes with normal RBC is linked to the virulence of the parasite and RBC polymorphisms that weaken rosetting confer protection against severe malaria. The adhesin PfEMP1 mediates the binding and specific antibodies prevent sequestration in the micro-vasculature, as seen in animal models. Here we demonstrate that epitopes targeted by rosette disrupting antibodies converge in the loop of subdomain 3 (SD3) which connects the h6 and h7 α-helices of PfEMP1-DBL1α. Both monoclonal antibodies and polyclonal IgG, that bound to epitopes in the SD3-loop, stained the surface of pRBC, disrupted rosettes and blocked direct binding of recombinant NTS-DBL1α to RBC. Depletion of polyclonal IgG raised to NTS-DBL1α on a SD3 loop-peptide removed the anti-rosetting activity. Immunizations with recombinant subdomain 1 (SD1), subdomain 2 (SD2) or SD3 all generated antibodies reacting with the pRBC-surface but only the sera of animals immunized with SD3 disrupted rosettes. SD3-sequences were found to segregate phylogenetically into two groups (A/B). Group A included rosetting sequences that were associated with two cysteine-residues present in the SD2-domain while group B included those with three or more cysteines. Our results suggest that the SD3 loop of PfEMP1-DBL1α is an important target of anti-rosetting activity, clarifying the molecular basis of the development of variant-specific rosette disrupting antibodies.

Highlights

The ability of P. falciparum parasitized RBC to form rosettes, clustering of uninfected erythrocytes around pRBC, is an adhesion property that varies in-between isolates which has been found associated with the virulence of the parasite [1,2,3,4,5,6,7]
To identify and characterize the structures in Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) that mediate rosetting we expressed three different species of NTSDBL1a of the rosetting parasites FCR3S1.2, R29 and PaloAlto varO as histidine-tagged proteins in E.coli
We report the generation of a number of antibodies to distinct NTS-DBL1a-domains that bind to the surface of pRBCs that disrupt rosettes or antibodies that only stain the pRBC-surface

Summary

Introduction

The ability of P. falciparum parasitized RBC (pRBC) to form rosettes, clustering of uninfected erythrocytes around pRBC, is an adhesion property that varies in-between isolates which has been found associated with the virulence of the parasite [1,2,3,4,5,6,7]. The vaso-occlusive effects of rosetting have been suggested to be important for the development of severe malaria [15]. Rosetting is mediated by the interaction of the parasite ligand Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) with serum-proteins and receptors on the human RBC surface [6,7].

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