Characterization of a protein correlated with the production of knob-like protrusions on membranes of erythrocytes infected with Plasmodium falciparum

Abstract

Membranes of erythrocytes infected with Plasmodium falciparum develop protrusions called "knobs." These protrusions are not apparent on erythrocytes infected with young parasites (rings) but develop with the growth of parasites to the trophozoite and schizont stages. The nature and origin of knobs were characterized by comparing the stagespecific proteins of two culture lines of P. falciparum, K+ and K-. K+ parasites produce knobs; K-parasites do not. Erythrocytes infected with both types of parasites were labeled metabolically and samples were analyzed by electrophoresis in sodium dodecyl sulfate/polyacrylamide gels. There were no apparent differences in Coomassie blue-stained or radioactive components of rings of K+ Membranes of erythrocytes infected with Plasmodium falciparum develop morphological alterations that were first described as "knob-like protrusions" (1). These protrusions are not apparent on erythrocytes that are infected with ring stages; they develop with the growth of parasites. In infected hosts, erythrocytes parasitized with multinucleate stages become sequestered and are not seen in the peripheral circulation. The knobs have been shown to be the sites of adhesion between sequestered erythrocytes and venous endothelial cells (2).A previous study (3) demonstrated that these protrusions were antigenically different from adjacent areas devoid of them. In an attempt to determine whether knob constituents were antigens of parasite origin that were incorporated into the host cell membrane, membrane fractions enriched in knobs were isolated from metabolically labeled infected erythrocytes and compared with fractions devoid of knobs. An additional labeled protein, with an apparent molecular weight of 70,000-80,000, was identified in samples enriched with knobs (4). From these results it could not be concluded with certainty whether this protein was a knob constituent or some other protein associated with membranes. Recently, it was noted that in cultures of an African strain of P. falciparum (FCR-3/Gambia) that had been maintained in flow vials (5) for >2 years by W. Trager some parasites failed to produce knobs (6). We were able to select for these parasites and obtain a culture line that showed mainly (about 99%) parasitized erythrocytes with smooth membranes (A. Kilejian and W. Trager, unpublished data). For purposes of discussion, the parent strain will be referred to as K+ and the derived culture line that does not produce knobs, as K-.This communication is a report on the comparison of stagespecific proteins of K+ and K-parasites. The results show that a metabolically labeled protein, of -80,000 molecular weight, that had been noted in a previous study (4) is correlated with the production of knobs. Two additional components that are synthesized during the development of merozoites have been identified.MATERIALS AND METHODS Parasites. P. falciparum (FCR-3/Gambia) was cultured in 100mm petri dishes in a candle jar (7). Cultures of K+ and Kparasites were synchronized by treatment with s...

Characterization of antigens from erythrocytic stages of Plasmodium falciparum reacting with human immune sera

“…Our results in this respect confirm and extend the earlier results of KILEJIAN (1979). We also detected a schizont-specific polypeptide of molecular weight 82 k-dalton which may be analogous to the 80 k-dalton polypeptides associated with knobs (KILEJIAN, 1979).…”

“…We also detected a schizont-specific polypeptide of molecular weight 82 k-dalton which may be analogous to the 80 k-dalton polypeptides associated with knobs (KILEJIAN, 1979).…”

N-terminal processing of proteins exported by malaria parasites

“…As the parasite matures within a parasitophorous vacuole (PV) inside the red blood cell (RBC), it extensively modifies the RBC to make it amenable for nutrient uptake and to prevent clearance by the spleen [2,3]. The parasite accomplishes this remodeling of the terminally differentiated RBC by exporting proteins across the parasite plasma membrane and the parasitophorous vacuolar membrane (PVM) to the red cell cytosol (RCC) or red cell membrane (RCM).…”

“…The parasite accomplishes this remodeling of the terminally differentiated RBC by exporting proteins across the parasite plasma membrane and the parasitophorous vacuolar membrane (PVM) to the red cell cytosol (RCC) or red cell membrane (RCM). A major example of a parasite-induced modification to the host RBC is the formation of knobs on the outer surface of the RCM [3]. These large protrusions consist of the parasite-encoded knob-associated histidine-rich protein (KAHRP) anchoring the immunovariant adhesin P. falciparum erythrocyte membrane protein 1 (PfEMP1) to the RBC cytoskeleton [4][5][6].…”

Histidine-rich domain of the knob protein of the human malaria parasite Plasmodium falciparum.

“…Several lines of evidence have suggested a relationship of KP with the histidine-rich protein (HRP) of Plasmodium lophurae, a polypeptide that contains over 70% histidine (10). KP is one of a few identified polypeptides of P. falciparum that incorporate relatively large amounts of exogenous histidine (8,9,11,12), and it is serologically crossreactive with the HRP (25).…”