A malaria invasion receptor, the 175-kilodalton erythrocyte binding antigen of Plasmodium falciparum recognizes the terminal Neu5Ac(alpha 2-3)Gal- sequences of glycophorin A.
Plasmodium falciparum malaria parasites invade human erythrocytes by means of a parasite receptor for erythrocytes, the 175-kD erythrocyte binding antigen (EBA-175). Similar to invasion efficiency, binding requires N-acetylneuraminic acid (Neu5Ac) on human erythrocytes, specifically the glycophorins. EBA-175 bound to erythrocytes with receptor-like specificity and was saturable. The specificity of EBA-175 binding was studied to determine if its binding is influenced either by simple electrostatic interaction with the negatively charged Neu5Ac (on the erythrocyte surface); or if Neu5Ac indirectly affected the conformation of an unknown ligand, or if Neu5Ac itself in specific linkage and carbohydrate composition was the primary ligand for EBA-175 as demonstrated for hemagglutinins of influenza viruses. Most Neu5Ac on human erythrocytes is linked to galactose by alpha 2-3 and alpha 2-6 linkages on glycophorin A. Soluble Neu5Ac by itself in solution did not competitively inhibit the binding of EBA-175 to erythrocytes, suggesting that linkage to an underlying sugar is required for binding in contrast to charge alone. Binding was competitively inhibited only by Neu5Ac(alpha 2-3)Gal-containing oligosaccharides. Similar oligosaccharides containing Neu5Ac(alpha 2-6)Gal-linkages had only slight inhibitory effects. Binding inhibition assays with modified sialic acids and other saccharides confirmed that oligosaccharide composition and linkage were primary factors for efficient binding. EBA-175 bound tightly enough to glycophorin A that the complex could be precipitated with an anti-glycophorin A monoclonal antibody. Selective cleavage of O-linked tetrasaccharides clustered at the NH2 terminus of glycophorin A markedly reduced binding in inhibition studies. We conclude that the Neu5Ac(a2,3)-Gal- determinant on O-linked tetrasaccharides of glycophorin A appear to be the preferential erythrocyte ligand for EBA-175.
Orlandi
P A
PA
Department of Immunology, Walter Reed Army Institute of Research, Washington, D.C. 20307-5100.
Klotz
F W
FW
Haynes
J D
JD
D000818:Animals; D000953:Antigens, Protozoan / Q000737:chemistry / Q000378:metabolism*; D000954:Antigens, Surface / Q000737:chemistry / Q000378:metabolism; D001667:Binding, Competitive; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D006021:Glycophorins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D010504:Periodic Acid / Q000494:pharmacology; D010963:Plasmodium falciparum / Q000276:immunology*; D015800:Protozoan Proteins; D012794:Sialic Acids / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology
D000953:Antigens, Protozoan; D000954:Antigens, Surface; D002352:Carrier Proteins; D006021:Glycophorins; D009844:Oligosaccharides; D015800:Protozoan Proteins; D012794:Sialic Acids; C065668:erythrocyte-binding antigen 175, Plasmodium; D010504:Periodic Acid; D019158:N-Acetylneuraminic Acid