Plasmodium falciparum erythrocyte membrane protein 1 is anchored to the actin-spectrin junction and knob-associated histidine-rich protein in the erythrocyte skeleton

A distinctive pathological feature of Plasmodium falciparum malaria is the endothelial attachment of erythrocytes infected with mature asexual-stage p arasites in microvessels of the major organs. Electron-dense protrusions de scribed as knobs are displayed on the surface of parasitized erythrocytes a nd act as attachment points in cytoadherence. Parasite-encoded knob-associa ted histidine-rich protein (KAHRP) is a major component of knobs found on t he cytoplasmic side of the host cell membrane. P. falciparum erythrocyte me mbrane protein 1 (PfEMP1) is a family of parasite-encoded cytoadherence rec eptors localized to knobs on the surface of parasitized erythrocytes. Despi te its high antigenic diversity, PfEMP1 has a remarkably conserved cytoplas mic domain. We demonstrate in this study that the cytoplasmic domain of PfE MP1 (VAR(CD)) binds to host spectrin and actin and to full-length KAHRP in vitro. Apparent dissociation constants determined for VAR(CD)/F-actin and V AR(CD)/KAHRP interactions are 44.9-16.4 and 10.7 +/- 2.2 nM, respectively. Further, we provide evidence that KAHRP polypeptides self-associate in solu tion to form structures similar to knobs and show binding of self-associate d KAHRP clusters to spectrin-actin-protein 4.1 complexes. Findings in this study suggest that PfEMP1 is localized to the knob in P. falciparum-infecte d erythrocytes by binding to the host spectrin-actin junction and to self-a ssociated KAHRP through its conserved cytoplasmic domain. (C) 2000 Elsevier Science B.V. All rights reserved.