A novel Plasmodium falciparum erythrocyte binding protein-2 (EBP2/BAEBL) involved in erythrocyte receptor binding

The 175-kDa erythrocyte binding protein (EBA-175) of Plasmodium falciparum and Duffy antigen binding proteins of P. vivax and P. knowlesi are members of a protein family. The features of this protein family include a cysteine-rich motif present in the erythrocyte receptor-binding domain. We identify here a novel 140-kDa P. falciparum erythrocyte binding protein (EBP2/BAEBL) containing the signature cysteine-rich motif by comparative analysis of gene sequence information. Polyclonal antibodies generated by immunization with an EBP2/BAEBL DNA vaccine immunoprecipitated a 140-kDa protein from P. falciparum schizont-infected erythrocyte lysates. Similar to EBA-175, the binding of EBP2/BAEBL to human erythrocytes was dependent on sialic acids because neuraminidase treatment of those erythrocytes rendered them incapable of binding, but differed from EBA-175 in that trypsin treatment decreased EBP2/BAEBL binding by only twofold compared to a 10-fold reduction in EBA-175 binding. Antibodies raised against the putative erythrocyte-binding domain of EBP2/BAEBL effectively blocked the binding of native EBP2/BAEBL to erythrocytes. These functional antibodies localize EBP2/BAEBL to the invasive apical end of the merozoite. We identify EBP2/BAEBL as a paralogue of EBA-175 and as a novel P. falciparum vaccine candidate.