Mapping regions containing binding residues within functional domains of Plasmodium vivax and Plasmodium knowlesi erythrocyte-binding proteins

Invasion of erythrocytes by malaria parasites is mediated by specific molec ular interactions. Whereas Plasmodium vivax and Plasmodium knowlesi use the Duffy blood group antigen, Plasmodium falciparum uses sialic acid residues of glycophorin A as receptors to invade human erythrocytes. P. knowlesi us es the Duffy antigen as well as other receptors to invade rhesus erythrocyt es by multiple pathways. Parasite ligands that bind these receptors belong to a family of erythrocyte-binding proteins (EBP). The EBP family includes the P. vivax and P. knowlesi Duffy-binding proteins, P. knowlesi beta and g amma proteins, which bind alternate receptors on rhesus erythrocytes, and P . falciparum erythrocyte-binding antigen (EBA-175), which binds sialic acid residues of human glycophorin A. Binding domains of each EBP lie in a cons erved N-terminal cysteine-rich region, region II, which contains around 330 amino acids with 12 to 14 conserved cysteines. Regions containing binding residues have now been mapped within P. vivax and P. knowlesi beta region I I. Chimeric domains containing P. vivax region II sequences fused to P. kno wlesi beta region II sequences were expressed on the surface of COS cells a nd tested for binding to erythrocytes, Binding residues of P. vivax region II lie in a 170-aa stretch between cysteines 4 and 7, and binding residues of P. knowlesi beta region II lie in a 53-aa stretch between cysteines 4 an d 5. Mapping regions responsible for receptor recognition is an important s tep toward understanding the structural basis for the interaction of these parasite ligands with host receptors.