We report the molecular identification of a sialic acid-independent host–parasite interaction in the Plasmodium falciparum malaria parasite invasion of RBCs. Two nonglycosylated exofacial regions of human band 3 in the RBC membrane were identified as a crucial host receptor binding the C-terminal processing products of merozoite surface protein 1 (MSP1). Peptides derived from the receptor region of band 3 inhibited the invasion of RBCs by P. falciparum. A major segment of the band 3 receptor (5ABC) bound to native MSP142 and blocked the interaction of native MSP142 with intact RBCs in vitro. Recombinant MSP119 (the C-terminal domain of MSP142) bound to 5ABC as well as RBCs. The binding of both native MSP142 and recombinant MSP119 was not affected by the neuraminidase treatment of RBCs, but sensitive to chymotrypsin treatment. In addition, recombinant MSP138 showed similar interactions with the band 3 receptor and RBCs, although the interaction was relatively weak. These findings suggest that the chymotrypsin-sensitive MSP1–band 3 interaction plays a role in a sialic acid-independent invasion pathway and reveal the function of MSP1 in the Plasmodium invasion of RBCs

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In Plasmodium falciparum malaria, erythrocyte invasion by circulating merozoites may occur via two distinct pathways involving either a sialic acid-dependent or -independent mechanism. Earlier, we identified two nonglycosylated exofacial regions of erythrocyte band 3 termed 5ABC and 6A as an important host receptor in the sialic acid-independent invasion pathway. 5ABC, a major segment of this receptor, interacts with the 42-kDa processing product of merozoite surface protein 1 (MSP1 42 ) through its 19-kDa C-terminal domain. Here, we show that two regions of merozoite surface protein 9 (MSP9), also known as acidic basic repeat antigen, interact directly with 5ABC during erythrocyte invasion by P. falciparum. Native MSP9 as well as recombinant polypeptides derived from two regions of MSP9 (MSP9/⌬1 and MSP9/⌬2) interacted with both 5ABC and intact erythrocytes. Soluble 5ABC added to the assay mixture drastically diminished the binding of MSP9 to erythrocytes. Recombinant MSP9/⌬1 and MSP9/⌬2 present in the culture medium blocked P. falciparum reinvasion into erythrocytes in vitro. Native MSP9 and MSP1 42 , the two ligands binding to the 5ABC receptor, existed as a stable complex. Our results establish a novel concept wherein the merozoite exploits a specific complex of co-ligands on its surface to target a single erythrocyte receptor during invasion. This new paradigm poses a new challenge in the development of a vaccine for blood stage malaria.