Identification of surface and internal antigens from spontaneously releasedPlasmodium falciparum merozoites by radio-iodination and metabolic labelling

Abstract

Spontaneously released merozoites from synchronous Plasmodium falciparum cultures were isolated in the presence of protease blocker. 1-5 X 10(10) merozoites were obtained in each experiment. The isolated merozoites possessed a thick surface coat and about 80% were invasive to human erythrocytes although they did not subsequently develop into ring stages. Tests using several analytical methods showed the merozoite preparations to be free of any erythrocyte contamination. Six labelled proteins were identified after surface radio-iodination, the largest with a molecular weight of 82 000. All six proteins were precipitated with various immune sera. Four other proteins with molecular weights of 200 000 and 160 000-145 000 (a triplet) were identified by precipitation with the same immune sera after metabolically labelling the merozoites. The six surface proteins were not prominent in the metabolically labelled preparations. Using these methods it is possible to identify and differentiate between surface and internal merozoite antigens.

A repetitive antigen of Plasmodium falciparum that is homologous to heat shock protein 70 of Drosophila melanogaster.

“…Intact erythrocytes from synchronized cultures at 8-12% parasitemia, containing ring-, trophozoite-, or schizont-stage parasites were surface labeled with 125I using lactoperoxidase (15). Freshly-collected merozoites were surface labeled with 125I by a modified lactoperoxidase procedure (16).…”

Two MSA 2 peptides that bind to human red blood cells are relevant to Plasmodium falciparum merozoite invasion

“…MSA 2, the second main molecule present on the Plasmodium falciparum merozoite surface, is a 35–56 kDa glycoprotein whose size and isoelectric point vary according to the parasite strain (1, 2). It is expressed during the late ring stage (≈ 12 h after merozoite invasion) and its maximal concentration is observed 42 h after invasion (3, 4). This antigen has been found to be associated with internal membranes in very mature multinucleated schizonts; it is present on the merozoite surface and residual bodies of all P. falciparum strains studied to date (5–9).…”

Isolation and functional characterization of Plasmodium falciparum merozoite antigens

“…Merozoites of P. falciparum (Colombianstrain FCB-I, originally isolated by C. Espinai, Instituto Nacional de Saiud, Bogota, and obtained from K. Rieckman, University of New Mexico, Albuquerque) were prepared according to the procedure of Mrema et ai. [16] and Heidrich et aL [41]. Briefly, highly synchronous cultures of asexual parasites [67,68] were obtained by alternate applications of the Sorbital and the Plasmagel [29,32,42,52] procedures.…”

“…It has been shown that most of the merozoite surface antigens stem from a high molecular weight glycoprotein precursor of 185-195 kDa present in schizonts [13,19,20,46]. During maturation of schizonts to merozoites, this precursor is processed to various smaller proteins which are then found on the merozoite surface [11,16]. Surface radiolabelling of purified merozoites has shown the protein composition of the outer surface to be relatively simple ( Fig.…”

“…Surface radiolabelling of purified merozoites has shown the protein composition of the outer surface to be relatively simple ( Fig. 1), consisting of only 5-6 major and a few minor constituents accessible to radio.iodination [10,16,20]. In one parasite strain at least 4 of these components at 83, 42, 36 and 19 kDa are derived from the precursor.…”