Authors

B Farrell¹; N Alam¹; M Hart²; A Jamwal¹; R Ragotte¹; H Walters-Morgan¹; S Draper¹; E Knuepfer²; MK Higgins¹;  ¹ University of Oxford, UK;  ² The Royal Veterinary College, UK

Discussion

Invasion of erythrocytes by Plasmodium falciparum, the deadliest human malaria parasite, is a tightly coordinated process involving many host-pathogen interactions. Among these is the essential interaction between PfRH5 and basigin on the red blood cell surface. PfRH5 is a member of the five-component PfPCRCR complex also containing PfCyRPA, PfRIPR, PfCSS and PfPTRAMP. Each of these five conserved proteins are essential to erythrocyte invasion, and each raises invasion-blocking antibodies or nanobodies, making them the leading blood stage malaria vaccine candidates. Despite its essential role, the molecular mechanism by which the PfPCRCR complex acts remains unclear. To gain insights, we determined the structure of the PfRCR complex comprising PfRH5, PfCyRPA and PfRIPR using cryo-EM. This reveals the structure of PfRIPR for the first time, showing that it is composed of a novel multi-domain core attached flexibly to an elongated tail. We find that PfRH5 is largely structurally unchanged when part of the PfRCR complex, and that a rigid disulphide-locked PfRH5 mediates efficient erythrocyte invasion, suggesting that it does not undergo large conformational changes. Additionally, we show that the parasite surface complex PfCSS-PfPTRAMP binds to the tail of PfRIPR, the target of anti-PfRIPR growth neutralising antibodies. Together with composite modelling of the PfRCR complex on the erythrocyte surface, these data indicate that the PfRCR complex acts to bridge the parasite and erythrocyte membranes, with a modular PfRIPR anchoring the complex to the parasite surface through its tail, presenting its structured core bound to PfCyRPA and PfRH5 such that they can engage with erythrocyte receptors. These findings provide novel insight into erythrocyte invasion and open the way to new approaches in rational vaccine design.