CeITOS, cell traversal protein for ookinetes and sporozoites; CSP, circumsporozoite protein; PfEBA, Plasmodium falciparum erythrocyte binding antigen; PfRH, Plasmodium falciparum reticulocyte-binding ...homologue; PLP, perforin-like protein; PSPECT1, sporozoite protein essential for cell traversal 1; PvRBP, Plasmodium vivax reticulocyte-binding proteins; TRAP, thrombospondin-related adhesive protein. https://doi.org/10.1371/journal.ppat.1007943.g001 Traversal precedes invasion Sporozoites are deposited into the dermis of the host upon the bite of an infected mosquito. Plasmodium parasites contain fourteen 6-cysteine domains containing proteins, which are conserved among different Plasmodium species and play crucial role in fertilization, parasitophorous vacuole membrane fitness, and immune evasion 19. ...several members of this family are potential vaccine candidates 20. The receptor-binding pocket of PvDBP has limited polymorphisms in contrast to the other segments that are highly polymorphic 46. ...it is possible to develop therapeutics targeting the P. vivax DBP-DARC interface to reduce malaria. ...through advanced tools in genetics, structure biology, and immunoparasitology, we have gained immense knowledge about the Plasmodium invasion machinery and its individual components in the last few decades.
Modern vaccine design has sought a minimalization approach, moving to the isolation of antigens from pathogens that invoke a strong neutralizing immune response. This approach has created safer ...vaccines but may limit vaccine efficacy due to poor immunogenicity. To combat global diseases such as COVID-19, malaria, and AIDS there is a clear urgency for more effective next-generation vaccines. One approach to improve the immunogenicity of vaccines is the use of nanoparticle platforms that present a repetitive array of antigen on its surface. This technology has been shown to improve antigen presenting cell uptake, lymph node trafficking, and B-cell activation through increased avidity and particle size. With a focus on design, we summarize natural platforms, methods of antigen attachment, and advancements in generating self-assembly that have led to new engineered platforms. We further examine critical parameters that will direct the usage and development of more effective platforms.
Toxoplasma gondii has evolved a number of strategies to evade immune responses in its many hosts. Previous genetic mapping of crosses between clonal type 1, 2, and 3 strains of T. gondii, which are ...prevalent in Europe and North America, identified two rhoptry proteins, ROP5 and ROP18, that function together to block innate immune mechanisms activated by interferon gamma (IFNg) in murine hosts. However, the contribution of these and other virulence factors in more genetically divergent South American strains is unknown. Here we utilized a cross between the intermediately virulent North American type 2 ME49 strain and the highly virulent South American type 10 VAND strain to map the genetic basis for differences in virulence in the mouse. Quantitative trait locus (QTL) analysis of this new cross identified one peak that spanned the ROP5 locus on chromosome XII. CRISPR-Cas9 mediated deletion of all copies of ROP5 in the VAND strain rendered it avirulent and complementation confirmed that ROP5 is the major virulence factor accounting for differences between type 2 and type 10 strains. To extend these observations to other virulent South American strains representing distinct genetic populations, we knocked out ROP5 in type 8 TgCtBr5 and type 4 TgCtBr18 strains, resulting in complete loss of virulence in both backgrounds. Consistent with this, polymorphisms that show strong signatures of positive selection in ROP5 were shown to correspond to regions known to interface with host immunity factors. Because ROP5 and ROP18 function together to resist innate immune mechanisms, and a significant interaction between them was identified in a two-locus scan, we also assessed the role of ROP18 in the virulence of South American strains. Deletion of ROP18 in South American type 4, 8, and 10 strains resulted in complete attenuation in contrast to a partial loss of virulence seen for ROP18 knockouts in previously described type 1 parasites. These data show that ROP5 and ROP18 are conserved virulence factors in genetically diverse strains from North and South America, suggesting they evolved to resist innate immune defenses in ancestral T. gondii strains, and they have subsequently diversified under positive selection.
In this issue of Structure, Raghavan et al. present the cryo-EM structures of the malaria-associated group A PfEMP1 HB3VAR03 head in both host receptor-free and receptor-bound states. The structures ...are complemented by biophysical analysis and introduce an innovative model in which host-receptor binding induces conformational changes in a PfEMP1 protein.
In this issue of Structure, Raghavan et al. present the cryo-EM structures of the malaria-associated group A PfEMP1 HB3VAR03 head in both host receptor-free and receptor-bound states. The structures are complemented by biophysical analysis and introduce an innovative model in which host-receptor binding induces conformational changes in a PfEMP1 protein.
Slicer and the Argonautes Joshua-Tor, Leemor; Tolia, Niraj H
Nature chemical biology,
01/2007, Volume:
3, Issue:
1
Journal Article
Peer reviewed
Though they started out as somewhat mysterious components of the RNAi effector complexes, Argonaute proteins have since taken center stage in RNAi gene silencing. They interact with small RNAs to ...effect gene silencing in all RNAi-related pathways known so far. We will review the dramatic advances in our understanding of the role of the Argonautes in RNAi through studies of their structure and function.
Pfs28 is a Plasmodium falciparum malaria transmission-blocking vaccine candidate that is anchored to the parasite surface through a C-terminal glycosylphosphatidylinositol (GPI) moiety, and plays a ...role in parasite survival in the mosquito midgut. Pfs28 contains epidermal growth factor (EGF)-like domains and is part of a family of sexual stage malaria proteins that includes the related vaccine antigen Pfs25. The lack of structural definition of Pfs28 and the immune response to this candidate has limited further malaria vaccine development for this antigen. Here, we present the crystal structure of Pfs28, examine its conservation with P. vivax Pvs28, and evaluate the cross-reactivity of Pfs28 to antibodies that recognize Pfs25. Pfs28 is comprised of four EGF-like domains stabilized by ten disulfide bridges with an overall architecture that highly resembles Pfs25. Despite the high sequence and structural similarity between these antigens, no cross reactivity of Pfs28 to anti-Pfs25 monoclonal antibodies could be demonstrated.
The morbidity caused by Plasmodium vivax infection is a major global burden.Duffy-binding protein (DBP) is a leading subunit vaccine candidate because of its role in binding and invading red blood ...cells.Natural infection elicits strain-transcending antibodies that block DBP and neutralize the parasite.Current DBP vaccines elicit large numbers of antibodies that are not cross-neutralizing.Structure-based design of DBP could elicit a more potent and durable antibody response.
Malaria caused by the Plasmodium vivax parasite is a major global health burden. Immunity against blood-stage infection reduces parasitemia and disease severity. Duffy-binding protein (DBP) is the primary parasite protein responsible for the invasion of red blood cells and it is a leading subunit vaccine candidate. An effective vaccine, however, is still lacking despite decades of interest in DBP as a vaccine candidate. This review discusses the reasons for targeting DBP, the challenges associated with developing a vaccine, and modern structural vaccinology methods that could be used to create an effective DBP vaccine. Next-generation DBP vaccines have the potential to elicit a broadly protective immune response and provide durable and potent protection from P. vivax malaria.
Malaria caused by the Plasmodium vivax parasite is a major global health burden. Immunity against blood-stage infection reduces parasitemia and disease severity. Duffy-binding protein (DBP) is the primary parasite protein responsible for the invasion of red blood cells and it is a leading subunit vaccine candidate. An effective vaccine, however, is still lacking despite decades of interest in DBP as a vaccine candidate. This review discusses the reasons for targeting DBP, the challenges associated with developing a vaccine, and modern structural vaccinology methods that could be used to create an effective DBP vaccine. Next-generation DBP vaccines have the potential to elicit a broadly protective immune response and provide durable and potent protection from P. vivax malaria.
Recently, Day et al. identified a receptor-binding site on the malaria parasite protein PfCyRPA that binds the host sugar Neu5Ac, and they found that disrupting this interaction impedes parasite ...growth. A map of the receptor-binding site identifies an attractive target for antimalarial vaccines and therapeutics.
Recently, Day et al. identified a receptor-binding site on the malaria parasite protein PfCyRPA that binds the host sugar Neu5Ac, and they found that disrupting this interaction impedes parasite growth. A map of the receptor-binding site identifies an attractive target for antimalarial vaccines and therapeutics.
Plasmodium vivax and Plasmodium knowlesi invasion depends on the parasite Duffy-binding protein DBL domain (RII-PvDBP or RII-PkDBP) engaging the Duffy antigen receptor for chemokines (DARC) on red ...blood cells. Inhibition of this key interaction provides an excellent opportunity for parasite control. There are competing models for whether Plasmodium ligands engage receptors as monomers or dimers, a question whose resolution has profound implications for parasite biology and control. We report crystallographic, solution and functional studies of RII-PvDBP showing that dimerization is required for and driven by receptor engagement. This work provides a unifying framework for prior studies and accounts for the action of naturally acquired blocking antibodies and the mechanism of immune evasion. We show that dimerization is conserved in DBL-domain receptor engagement and propose that receptor-mediated ligand dimerization drives receptor affinity and specificity. Because dimerization is prevalent in signaling, our studies raise the possibility that induced dimerization may activate pathways for invasion.
Plasmodium parasites use specialized ligands which bind to red blood cell (RBC) receptors during invasion. Defining the mechanism of receptor recognition is essential for the design of interventions ...against malaria. Here, we present the structural basis for Duffy antigen (DARC) engagement by P. vivax Duffy binding protein (DBP). We used NMR to map the core region of the DARC ectodomain contacted by the receptor binding domain of DBP (DBP-RII) and solved two distinct crystal structures of DBP-RII bound to this core region of DARC. Isothermal titration calorimetry studies show these structures are part of a multi-step binding pathway, and individual point mutations of residues contacting DARC result in a complete loss of RBC binding by DBP-RII. Two DBP-RII molecules sandwich either one or two DARC ectodomains, creating distinct heterotrimeric and heterotetrameric architectures. The DARC N-terminus forms an amphipathic helix upon DBP-RII binding. The studies reveal a receptor binding pocket in DBP and critical contacts in DARC, reveal novel targets for intervention, and suggest that targeting the critical DARC binding sites will lead to potent disruption of RBC engagement as complex assembly is dependent on DARC binding. These results allow for models to examine inter-species infection barriers, Plasmodium immune evasion mechanisms, P. knowlesi receptor-ligand specificity, and mechanisms of naturally acquired P. vivax immunity. The step-wise binding model identifies a possible mechanism by which signaling pathways could be activated during invasion. It is anticipated that the structural basis of DBP host-cell engagement will enable development of rational therapeutics targeting this interaction.
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