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.