Erythrocyte binding protein homologues of rodent malaria parasites

Erythrocyte invasion by malaria parasites requires specific molecular interactions between the merozoite and erythrocyte surface receptors. A well- conserved, functionally important family of erythrocyte binding proteins is the EBP family. The EBP family includes the Plasmodium vivax/P. knowlesi Duffy binding protein (DBP) family and the P. falciparum erythrocyte binding antigen-175 (EBA-175). The EBP are transmembrane proteins, characterized by two conserved cysteine-rich domains, expressed in the micronemes of invasive merozoites. Oligonucleotide primers matching the region encoding the carboxyl cysteine-rich domain of the EBA-175 were used in a polymerase chain reaction to identify homologous genes in P. berghei and P. yoelii yoelii, leading to the isolation of a P. berghei partial genomic clone. This clone contained a 323 bp region that had high deduced amino acid sequence similarity to the amino acid sequences of the carboxyl cysteine-rich domains of the DBP family and EBA-175. The P. berghei carboxyl cysteine-rich domain was followed by a putative transmembrane domain and a cytoplasmic domain, demonstrating an exon-intron structure at the 3' end homologous to P. vivax dbp and P. falciparum eba-175. The carboxyl cysteine-rich domain is also highly conserved among P. berghei, P. y. yoelii, P. chabaudi and P. vinckei and is encoded by a single copy gene. Antisera prepared against the carboxyl cysteine-rich domain of the rodent malaria EBP homologues reacted with a 120 and 128 kDa protein doublet on Western blots of P. berghei parasite antigen and showed an apical localization pattern within merozoites by indirect immunofluorescence assays.