Oral Presentation Lorne Infection and Immunity 2023

PCRCR complex is essential for invasion of human erythrocytes by Plasmodium falciparum (#31)

Stephen W Scally 1 , Tony Triglia 1 , Cindy Evelyn 1 , Benjamin A Seager 1 , Michal Pasternak 1 , Pailene S Lim 1 , Julie Healer 1 , Niall D Geogheghan 1 , Amy Adair 1 , Wai-Hong Tham 1 , Laura F Dagley 1 , Kelly L Rogers 1 , Alan F Cowman 1
  1. Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia

The most severe form of malaria is caused by Plasmodium falciparum. These parasites invade human erythrocytes in a complex multistep process that ultimately ends with the internalization of the parasite. An essential step in this process involves the ligand PfRh5, which forms a complex with the cysteine-rich protective antigen (CyRPA) and the PfRh5-interacting protein (PfRipr; RCR complex) and binds basigin on the host cell. However, it was unclear what tethers the RCR complex to the parasite surface, as all three proteins lack a transmembrane region or GPI anchor. We identified a heteromeric disulphide-linked complex consisting of the Plasmodium Thrombospondin-Related Apical Merozoite Protein (PfPTRAMP) and the Cysteine rich Small-Secreted protein (PfCSS) and have shown it binds RCR to form a pentameric complex PCRCR. Importantly, PfPTRAMP has a single transmembrane domain and likely tethers the complex to the parasite. Using P. falciparum lines with conditional knockouts and invasion inhibitory nanobodies to both PfPTRAMP and PfCSS we utilised lattice light-sheet microscopy and show they are essential for parasite invasion. The PCRCR complex functions to anchor the contact between parasite and erythrocyte membranes brought together by strong parasite deformations. Furthermore, we determined the X-ray crystal structure of PfCSS in complex with one neutralizing and one non-neutralizing nanobody. Our results define the function of the PCRCR complex and identify invasion neutralising epitopes providing a roadmap for structure-guided development of these proteins for a blood stage malaria vaccine.