Full-length extracellular region of the var2CSA variant of PfEMP1 is required for specific, high-affinity binding to CSA.
Pregnancy-associated malaria (PAM) is a serious consequence of sequestration of Plasmodium falciparum-parasitized erythrocytes (PE) in the placenta through adhesion to chondroitin sulfate A (CSA) present on placental proteoglycans. Recent work implicates var2CSA, a member of the PfEMP1 family, as the mediator of placental sequestration and as a key target for PAM vaccine development. Var2CSA is a 350 kDa transmembrane protein, whose extracellular region includes six Duffy-binding-like (DBL) domains. Due to its size and high cysteine content, the full-length var2CSA extracellular region has not hitherto been expressed in heterologous systems, thus limiting investigations to individual recombinant domains. Here we report for the first time the expression of the full-length var2CSA extracellular region (domains DBL1X to DBL6epsilon) from the 3D7 parasite strain using the human embryonic kidney 293 cell line. We show that the recombinant extracellular var2CSA region is correctly folded and that, unlike the individual DBL domains, it binds with high affinity and specificity to CSA (K(D) = 61 nM) and efficiently inhibits PE from binding to CSA. Structural characterization by analytical ultracentrifugation and small-angle x-ray scattering reveals a compact organization of the full-length protein, most likely governed by specific interdomain interactions, rather than an extended structure. Collectively, these data suggest that a high-affinity, CSA-specific binding site is formed by the higher-order structure of the var2CSA extracellular region. These results have important consequences for the development of an effective vaccine and therapeutic inhibitors.
Srivastava
Anand
A
Institut Pasteur, Unité de Biologie des Interactions Hôte-Parasite, Centre National de la Recherche Scientifique Unité de Recherche Associée 2581, 25 rue du Docteur Roux, F-75724 Paris Cedex 15, France.
Gangnard
Stéphane
S
Round
Adam
A
Dechavanne
Sébastien
S
Juillerat
Alexandre
A
Raynal
Bertrand
B
Faure
Grazyna
G
Baron
Bruno
B
Ramboarina
Stéphanie
S
Singh
Saurabh Kumar
SK
Belrhali
Hassan
H
England
Patrick
P
Lewit-Bentley
Anita
A
Scherf
Artur
A
Bentley
Graham A
GA
Gamain
Benoît
B
D000818:Animals; D000953:Antigens, Protozoan / Q000737:chemistry* / Q000378:metabolism*; D002460:Cell Line; D011508:Chondroitin Sulfate Proteoglycans / Q000378:metabolism; D002809:Chondroitin Sulfates / Q000378:metabolism*; D002942:Circular Dichroism; D058575:Decorin; D004912:Erythrocytes / Q000378:metabolism / Q000469:parasitology; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005110:Extracellular Space / Q000737:chemistry*; D005260:Female; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D010271:Parasites / Q000378:metabolism; D010920:Placenta / Q000378:metabolism; D010963:Plasmodium falciparum / Q000378:metabolism*; D011247:Pregnancy; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011509:Proteoglycans / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D000953:Antigens, Protozoan; D011508:Chondroitin Sulfate Proteoglycans; C546878:DCN protein, human; D058575:Decorin; D016326:Extracellular Matrix Proteins; D020033:Protein Isoforms; D011509:Proteoglycans; D011994:Recombinant Proteins; C512601:VAR2CSA protein, Plasmodium falciparum; D002809:Chondroitin Sulfates