Plasmodium falciparum: D260, an intraerythrocytic parasite protein, is a member of the glutamic acid dipeptide-repeat family of proteins.

Members of a serologically cross-reacting family of proteins including Ag332 and Pf11.1, megadalton proteins of schizont-infected red blood cells, and gametocytes, respectively, and Pf155-RESA, a 155-kDa protein of ring-infected red blood cells, have been reported to share amino acid repeat sequences. These repeats are rich in glutamic acid dipeptides postulated to be involved in generating serologic cross-reactivity. We report the identification and characterization of another member of this cross-reacting family, a 260-kDa glutamic acid-rich intraerythrocytic protein. Human antibodies affinity purified on the 260-kDa region of Western boots of trophozoite proteins of Plasmodium falciparum were used to screen a trophozoite-stage lambda gt11 cDNA library. A 1.8-kb clone was identified and human antibodies were affinity purified on the expressing clone. Using this affinity-purified antibody and the 1.8-kb clone, the corresponding protein, its gene, and its chromosomal location were investigated. The 260-kDa corresponding protein serologically cross-reacts with Pf155-RESA, but is the product of a different gene. The 260-kDa protein is Triton X-100 soluble and is variable in molecular weight in different isolates. Immunoprecipitation of [35S]methionine-labeled infected red blood cells indicates that the protein is synthesized throughout the intraerythrocytic cycle but is most prominent in schizonts. The protein, as has been shown previously, is not immunoprecipitated from 125I surface-labeled infected red blood cells and is thus not PfEMP1, the antigen associated with cytoadherence. Indirect fluorescent antibody studies using fixed infected red blood cells suggest that the protein is localized to the periphery of the intraerythrocytic parasite.