P. falciparum EBA-181 ligand - searching for the receptor on human erythrocytes

Malaria caused by Plasmodium is responsible for approximately 250 million clinical cases and 600,000 deaths per year, mostly in Africa. Our understanding of Plasmodium parasite biology remains incomplete. The key step of Plasmodium invasion is the blood stage, which is mediated by Erythrocyte binding-like (EBL) and Reticulocyte binding-like (RBL) proteins. Three P. falciparum EBL proteins and their receptors are functional: EBA-175 - Glycophorin A (GPA), EBL-1 - Glycophorin B (GPB), and EBA-140 - Glycophorin C (GPC). Because the fourth EBA-181 ligand recognizes the mysterious erythrocyte receptor Z, which remains unknown, we aimed to characterize its specificity and search for its receptor. The Surface Plasmon Resonance method was employed to evaluate the interaction of the recombinant EBA-181 ligand with sugar moieties and the Rh2b ligand. We have demonstrated that the EBA-181 ligand binds to Neu5Ac and Neu5Gc sialic acids, interacting with the Rh2b protein with a dissociation constant of approximately 3 µM. Moreover, the EBA-181 protein binds to about 100 kDa erythrocyte membrane protein. The P. falciparum EBA-181 merozoite ligand binding was shown to be sialic acid-dependent. It seems that the Rh2b merozoite protein might be the co-ligand cooperating with EBA-181 in erythrocyte invasion. Finally, our studies suggested that erythrocyte Band 3 protein may be a putative receptor for the EBA-181 ligand.