title: Plasmodium falciparum malaria: association of knobs on the surface of infected erythrocytes with a histidine-rich protein and the erythrocyte skeleton.
abstract: Plasmodium falciparum-infected erythrocytes (RBC) develop surface protrusions (knobs) which consist of electron-dense submembrane cups and the overlying RBC plasma membrane. Knobs mediate cytoadherence to endothelial cells. Falciparum variants exist that lack knobs. Using knobby (K+) and knobless (K-) variants of two strains of P. falciparum, we confirmed Kilejian's original observation that a histidine-rich protein occurred in K+ parasites but not K- variants (Kilejian, A., 1979, Proc. Natl. Acad. Sci. USA, 76:4650-4653; and Kilejian, A., 1980, J. Exp. Med., 151:1534-1538). Two additional histidine-rich proteins of lower molecular weight were synthesized by K+ and K- variants of both strains. We used differential detergent extraction and thin-section electron microscopy to investigate the subcellular location of the histidine-rich protein unique to K+ parasites. Triton X-100, Zwittergent 314, cholic acid, CHAPS, and Triton X-100/0.6 M KCl failed to extract the unique histidine-rich protein. The residues insoluble in these detergents contained the unique histidine-rich protein and electron-dense cups. The protein was extracted by 1% SDS and by 1% Triton X-100/9 M urea. The electron-dense cups were missing from the insoluble residues of these detergents. The electron-dense cups and the unique histidine-rich protein appeared to be associated with the RBC skeleton, particularly RBC protein bands 1, 2, 4.1, and 5. We propose that the unique histidine-rich protein binds to the RBC skeleton to form the electron-dense cup. The electron-dense cup produces knobs by forming focal protrusions of the RBC membrane. These protrusions are the specific points of attachment between infected RBC and endothelium.
mesh_terms: D000818:Animals; D001798:Blood Proteins; D002427:Cebidae; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000648:ultrastructure*; D006023:Glycoproteins / Q000097:blood*; D006461:Hemolysis; D008288:Malaria / Q000097:blood*; D008854:Microscopy, Electron; D010963:Plasmodium falciparum / Q000472:pathogenicity*; D011506:Proteins / Q000302:isolation & purification; D000099053:Histidine-Rich Glycoprotein
chemical_list: D001798:Blood Proteins; D006023:Glycoproteins; D011506:Proteins; D000099053:Histidine-Rich Glycoprotein