Structure of the malaria vaccine candidate antigen CyRPA and its complex with a parasite invasion inhibitory antibody

Abstract

Invasion of erythrocytes by Plasmodial merozoites is a composite process involving the interplay of several proteins. Among them, the Plasmodium falciparum Cysteine-Rich Protective Antigen (PfCyRPA) is a crucial component of a ternary complex, including Reticulocyte binding-like Homologous protein 5 (PfRH5) and the RH5-interacting protein (PfRipr), essential for erythrocyte invasion. Here, we present the crystal structures of PfCyRPA and its complex with the antigen-binding fragment of a parasite growth inhibitory antibody. PfCyRPA adopts a 6-bladed β-propeller structure with similarity to the classic sialidase fold, but it has no sialidase activity and fulfills a purely non-enzymatic function. Characterization of the epitope recognized by protective antibodies may facilitate design of peptidomimetics to focus vaccine responses on protective epitopes. Both in vitro and in vivo anti-PfCyRPA and anti-PfRH5 antibodies showed more potent parasite growth inhibitory activity in combination than on their own, supporting a combined delivery of PfCyRPA and PfRH5 in vaccines.DOI: http://dx.doi.org/10.7554/eLife.20383.001

Neutralising antibodies block the function of Rh5/Ripr/CyRPA complex during invasion of Plasmodium falciparum into human erythrocytes

“…The anti‐CyRPA mAb 8A7 blocks assembly of PfRh5 into the complex whereas 3D1 and 5B12 do not, despite them all binding to common epitopes. Parallel studies of the CyRPA crystal structure determined that monoclonal antibodies 8A7 and C12 in fact bind to proximal but not identical regions of CyRPA, which may explain their differential abilities to block the Rh5‐CyRPA interaction (Chen et al, ; Favuzza et al, ). Based on cryo‐EM and crosslinking studies (Wong et al, ), the C‐terminal tail of Rh5 interacts with blade 1 beta sheet of CyRPA.…”

“…In the parasite, PfRh5 forms a trimeric complex with the cysteine‐rich protective antigen (CyRPA) and PfRh5‐interacting protein (PfRipr) during merozoite invasion (Chen et al, ; Reddy et al, ; Volz et al, ). The structure of CyRPA has also been solved both by itself and in complex with invasion inhibitory monoclonal antibodies (mAbs), revealing a six‐bladed β‐propeller fold (Chen et al, ; Favuzza et al, ). The crystal structure of PfRipr in isolation has not been solved; however, the structure of the PfRh5/CyRPA/PfRipr complex has recently been determined by cryo‐electron microscopy (Wong et al, ).…”

“…Antibodies to recombinant PfRh5 and basigin, as well as soluble basigin itself, block the function of PfRh5 consequently inhibiting merozoite invasion (Bustamante et al, ; Crosnier et al, ; Douglas et al, ). Rabbit and mouse antibodies raised to recombinant CyRPA and PfRipr also inhibit the function of these proteins and block merozoite invasion (Chen et al, , ; Douglas et al, ; Favuzza et al, ; Reddy et al, ). Furthermore, vaccination of Aotus monkeys with PfRh5 protected individuals against challenge with a heterologous strain of P. falciparum (Douglas et al, ).…”

“…Rabbit and mouse antibodies raised to recombinant CyRPA and PfRipr also inhibit the function of these proteins and block merozoite invasion (Chen et al, 2011(Chen et al, , 2017Douglas et al, 2015;Favuzza et al, 2017;Reddy et al, 2014). Furthermore, vaccination of Aotus monkeys with PfRh5 protected individuals against challenge with a heterologous strain of P. falciparum (Douglas et al, 2015).…”

Plasmodium falciparum subtilisin‐like ookinete protein SOPT plays an important and conserved role during ookinete infection of the Anopheles stephensi midgut

“…The function of many is unknown, but for a number an important role in various cellular functions have been shown (Eyers and Murphy, 2016), including regulation of active enzyme counterparts, signaling, substrate trafficking and in many pathogens also modulation of host immune responses (Reynolds and Fischer, 2015). Plasmodium pseudoenzymes include CyRPA (cysteine-rich protective antigen), a pseudosialidase that forms a multi-protein complex that is essential for merozoite invasion of erythrocytes (Chen et al, 2017;Favuzza et al, 2017), and SERA5, a non-active papain-like protease thought to regulate the function of SERA6 in merozoite egress by controlling access to its substrates (Stallmach et al, 2015). A non-catalytic ATP-dependent caseinolytic protease, ClP-R, has also recently been identified within the parasite apicoplast, although its function is currently unknown (El Bakkouri et al, 2013).…”