Sequential roles for red blood cell binding proteins enable phased commitment to invasion for malaria parasites

Abstract

Invasion of red blood cells (RBCs) by Plasmodium merozoites is critical to their continued survival within the host. Two major protein families, the Duffy binding-like proteins (DBPs/EBAs) and the reticulocyte binding like proteins (RBLs/RHs) have been studied extensively in P. falciparum and are hypothesized to have overlapping, but critical roles just prior to host cell entry. The zoonotic malaria parasite, P. knowlesi, has larger invasive merozoites and contains a smaller, less redundant, DBP and RBL repertoire than P. falciparum. One DBP (DBPα) and one RBL, normocyte binding protein Xa (NBPXa) are essential for invasion of human RBCs. Taking advantage of the unique biological features of P. knowlesi and iterative CRISPR-Cas9 genome editing, we determine the precise order of key invasion milestones and demonstrate distinct roles for each family. These distinct roles support a mechanism for phased commitment to invasion and can be targeted synergistically with invasion inhibitory antibodies.

PlasmodiumRON11 triggers biogenesis of the merozoite rhoptry pair and is essential for erythrocyte invasion

“…Interestingly, we observed by live imaging that -RON11 merozoites that are unable to complete invasion, are still able to induce strong deformations on RBCs. Since gliding motility is required for deformation (Yahata et al 2021; Hart et al 2023), this suggests that RON11 may not be required for motility of P. falciparum merozoites, unlike previously observed for P. berghei sporozoites (Bantuchai et al 2019). RON11 deficient merozoites engage and deform host cells for significantly longer before the RBCs undergo echinocytosis, a process that is thought to follow rhoptry secretion (Weiss et al 2015).…”

“…Invasion is a rapid and complex process involving multiple steps. Newly egressed merozoites initiate an early attachment, leading to RBC deformation and merozoite reorientation (Groomes, Kanjee, and Duraisingh 2022; Hart et al 2023; Weiss et al 2015). Once its apical end is reoriented towards the RBC, the merozoite appears to form a pore in the RBC membrane, secretes proteins from rhoptries into the RBC, which together with micronemal proteins on the merozoite membrane, form an irreversible tight junction at the interface merozoite-RBC (Cova, Lamarque, and Lebrun 2022; Geoghegan et al 2021; Riglar et al 2011; Vulliez-Le Normand et al 2012; Weiss et al 2015).…”

Conservation of red blood cell signalling in Plasmodium merozoite invasion

“…In contrast, PkDBPα and PkNBPXa are essential for P. knowlesi invasion into human RBCs. PkNBPXa-receptor interaction was shown to mediate RBC deformation, which is a key step that commits the parasite to invasion (Hart et al, 2022;Yahata et al, 2021). PkDBPα-DARC interaction was instead proposed to function at a step downstream of PkNBPXa before rhoptry secretion and reorientation (Hart et al, 2022).…”