Plasmodium falciparum is the causative agent of the most severe form of malaria in humans. The merozoite, an extracellular stage of the parasite lifecycle, invades erythrocytes in which they develop. The most abundant protein on the surface of merozoites is Merozoite Surface Protein 1 (MSP1), which consists of four processed fragments. Studies have indicated that MSP1 interacts with other peripheral merozoite surface proteins to form a large complex. Successful invasion of merozoites into host erythrocytes is dependent on this protein complex; however, the identity of all components and its function remain largely unknown. We have shown that the peripheral merozoite surface proteins, MSPDBL1 and MSPDBL2 are part of the large MSP1 complex. Using Surface Plasmon Resonance, we determined the binding affinities of MSPDBL1 and MSPDBL2 to MSP1 to be 171.6 nM and 445.4 nM respectively. Both proteins bind to 3 of the 4 proteolytically cleaved fragments of MSP1 (P42, P38 and P83). In addition, MSPDBL1 and MSPDBL2, but not MSP1, bind directly to human erythrocytes. This demonstrates that the MSP1 complex acts as a platform for display of MSPDBL1 and MSPDBL2 on the merozoite surface for binding to receptors on the erythrocyte and invasion.
American Society for Biochemistry and Molecular Biology