Engagement rules that underpin DBL-DARC interactions for ingress of Plasmodium knowlesi and Plasmodium vivax into human erythrocytes

Plasmodium parasites are unicellular organisms that cause malaria and ensuing morbidity in afflicted regions of the world. Although the most dreadful of human malaria parasites is P. falciparum, its variant P. vivax is common in India, South East Asia and Latin America. In addition, a fifth human parasite called P. knowlesi is able to cause infections in humans in some regions. P. vivax has a wide distribution with 40% of world9s population at risk of infection and 70-130 million annual cases. The molecular mechanisms by which P. knowlesi and P. vivax invade human red blood cells have long been studied. Malaria parasite erythrocytic stages comprise of repeated propagation of parasites via cyclical invasion of host RBCs via dedicated receptor-ligand interactions. A family of erythrocyte-binding antigens (EBAs) that include P. knowlesi and P. vivax Duffy-binding proteins (PvDBP and PkDBP respectively) attach to duffy antigen (DARC) on human erythrocytes for invasion via their duffy binding-like domains (DBLs). Here, we provide a comprehensive overview that presents new insights on the atomic resolution interactions that underpin the binding of Duffy antigen on human red blood cells (DARC) with P. knowlesi and P. vivax DBL domains. Using extensive structural and biochemical data from the past decade, we provide a novel, testable and overarching model that fully rationalizes even contradictory pieces of evidence that have so far existed in the literature. We resolve the conundrum of how parasite-encoded DBL domains recognize human DARC and its two sulfated tyrosine residues. We provide evidence of two distinct DARC binding sites on P. knowlesi and P. vivax DBLs that together likely engage the extracellular domain of DARC. These analyses are important for both malaria vaccine and inhibitor development efforts that are targeted at abrogating DARC-DBL interactions as an avenue to prevent invasion of malaria parasites into human red blood cells.