An Invariant Protein That Colocalizes With VAR2CSA on Plasmodium falciparum-Infected Red Cells Binds to Chondroitin Sulfate A

Background Plasmodium falciparum-infected red blood cells (iRBCs) bind and sequester in deep vascular beds, causing malaria-related disease and death. In pregnant women, VAR2CSA binds to chondroitin sulfate A (CSA) and mediates placental sequestration, making it the major placental malaria (PM) vaccine target. Methods In this study, we characterize an invariant protein associated with PM called P falciparum chondroitin sulfate A ligand (PfCSA-L). Results Recombinant PfCSA-L binds both placental CSA and VAR2CSA with nanomolar affinity, and it is coexpressed on the iRBC surface with VAR2CSA. Unlike VAR2CSA, which is anchored by a transmembrane domain, PfCSA-L is peripherally associated with the outer surface of knobs through high-affinity protein-protein interactions with VAR2CSA. This suggests that iRBC sequestration involves complexes of invariant and variant surface proteins, allowing parasites to maintain both diversity and function at the iRBC surface. Conclusions The PfCSA-L is a promising target for intervention because it is well conserved, exposed on infected cells, and expressed and localized with VAR2CSA. PfCSA-L, an invariant protein that binds both CSA and VAR2CSA with high affinity, is exported to the iRBC surface and colocalizes with VAR2CSA. PfCSA-L is the target of antibodies in multigravid women and a promising placental malaria vaccine target.