A family of erythrocyte binding proteins of malaria parasites.

  • Adams J
  • Sim B
  • Dolan S
 et al. 
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Malaria erythrocyte binding proteins use the Duffy blood group antigen (Plasmodium vivax and Plasmodium knowlesi) and sialic acid (Plasmodiumfalciparum) on the eryth-rocyte surface as receptors. We had previously cloned the one P. vivar gene, the one P. fakiparum gene, and part of one of the three P. knowlesi genes encoding these erythrocyte binding proteins and described the homology between the P. knowlesi and P. vivax genes. We have completed the cloning and sequencing of the three P. knowlesi genes and identified introns in the P. vivax and P. falciparum genes that correct the previously published deduced amino acid sequences. All have similar structures, with one or two exons encoding the signal sequence and the erythrocyte binding domain, an exon encod-ing the transmembrane domain, and two exons encoding the cytoplasmic domain with the exception of the P. knowlesi (3 gene. The regions of amino acid sequence homology among all the genes are the 5' and 3' cysteine-rich regions of the eryth-rocyte binding domain. On the basis of gene structure and amino acid homology, we propose that the Duffy binding proteins and the sialic acid binding protein are members of a gene family. The level of conservation (-70%) of the deduced amino acid sequences in the 5' cysteine-rich region between the P. vivax protein and the three P. knowlesi proteins is as great as between the three P. knowlesi proteins themselves; the P. knowlesi (3 protein just 3' to this cysteine-rich region is homol-ogous to the P. vivax protein but not to the other P. knowlesi proteins. Conservation of amino acid sequences among these organisms, separated in evolution, may indicate the regions where the adhesin function resides. Invasion of erythrocytes by malaria parasites is dependent on binding of parasite proteins to receptors on the erythrocyte surface (1). Plasmodium knowlesi and Plasmodium vivax require interaction with the Duffy blood group antigen (Duffy-positive human erythrocytes) and cannot invade Duffy-negative human erythrocytes. Plasmodium falci-parum, the major human malaria, can invade Duffy-negative and -positive erythrocytes equally well and, instead, binds specifically to neuraminidase-sensitive sialic acids on eryth-rocyte glycophorin. Neuraminidase treatment of erythro-cytes does not reduce invasion by P. knowlesi. Thus, differ-ent parasite species use different receptors for invasion of erythrocytes (1). The parasite proteins that bind to the Duffy blood group antigen in P. knowlesi (2) and P. vivax (3) or to sialic acid in P. falciparum (4) were identified, and the genes encoding them were partially cloned and sequenced (5-7). The P. falciparum protein that binds to erythrocytes has a molecular mass of 175 kDa and was called erythrocyte binding antigen 175 (EBA175). Because it has now been shown that EBA175 binds specifically to sialic acid (8, 9), we

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  • J. H. Adams

  • B. K. Sim

  • S. A. Dolan

  • X. Fang

  • D. C. Kaslow

  • L. H. Miller

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