I02-Macromolecular Crystallography
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Open Access
Abstract: Structure-guided vaccine design provides a route to elicit a focused immune response against the most functionally important regions of a pathogen surface. This can be achieved by identifying epitopes for neutralizing antibodies through structural methods and recapitulating these epitopes by grafting their core structural features onto smaller scaffolds. In this study, we conducted a modified version of this protocol. We focused on the PfEMP1 protein family found on the surfaces of erythrocytes infected with Plasmodium falciparum. A subset of PfEMP1 proteins bind to endothelial protein C receptor (EPCR), and their expression correlates with development of the symptoms of severe malaria. Structural studies revealed that PfEMP1 molecules present a helix-kinked-helix motif that forms the core of the EPCR-binding site. Using Rosetta-based design, we successfully grafted this motif onto a three-helical bundle scaffold. We show that this synthetic binder interacts with EPCR with nanomolar affinity and adopts the expected structure. We also assessed its ability to bind to antibodies found in immunized animals and in humans from malaria-endemic regions. Finally, we tested the capacity of the synthetic binder to effectively elicit antibodies that prevent EPCR binding and analyzed the degree of cross-reactivity of these antibodies across a diverse repertoire of EPCR-binding PfEMP1 proteins. Despite our synthetic binder adopting the correct structure, we find that it is not as effective as the CIDRα domain on which it is based for inducing adhesion-inhibitory antibodies. This cautions against the rational design of focused immunogens that contain the core features of a ligand-binding site of a protein family, rather than those of a neutralizing antibody epitope.
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Feb 2021
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I23-Long wavelength MX
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Diamond Proposal Number(s):
[23459]
Open Access
Abstract: The deadly symptoms of malaria occur as Plasmodium parasites replicate within blood cells. Members of several variant surface protein families are expressed on infected blood cell surfaces. Of these, the largest and most ubiquitous are the Plasmodium-interspersed repeat (PIR) proteins, with more than 1,000 variants in some genomes. Their functions are mysterious, but differential pir gene expression associates with acute or chronic infection in a mouse malaria model. The membership of the PIR superfamily, and whether the family includes Plasmodium falciparum variant surface proteins, such as RIFINs and STEVORs, is controversial. Here we reveal the structure of the extracellular domain of a PIR from Plasmodium chabaudi. We use structure-guided sequence analysis and molecular modeling to show that this fold is found across PIR proteins from mouse- and human-infective malaria parasites. Moreover, we show that RIFINs and STEVORs are not PIRs. This study provides a structure-guided definition of the PIRs and a molecular framework to understand their evolution.
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Nov 2020
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I03-Macromolecular Crystallography
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Ivan
Campeotto
,
Francis
Galaway
,
Shahid
Mehmood
,
Lea K.
Barfod
,
Doris
Quinkert
,
Vinayaka
Kotraiah
,
Timothy W.
Phares
,
Katherine E.
Wright
,
Ambrosius P.
Snijders
,
Simon J.
Draper
,
Matthew K.
Higgins
,
Gavin J.
Wright
Diamond Proposal Number(s):
[23459]
Open Access
Abstract: Plasmodium falciparum RH5 is a secreted parasite ligand that is essential for erythrocyte invasion through direct interaction with the host erythrocyte receptor basigin. RH5 forms a tripartite complex with two other secreted parasite proteins, CyRPA and RIPR, and is tethered to the surface of the parasite through membrane-anchored P113. Antibodies against RH5, CyRPA, and RIPR can inhibit parasite invasion, suggesting that vaccines containing these three components have the potential to prevent blood-stage malaria. To further explore the role of the P113-RH5 interaction, we selected monoclonal antibodies against P113 that were either inhibitory or noninhibitory for RH5 binding. Using a Fab fragment as a crystallization chaperone, we determined the crystal structure of the RH5 binding region of P113 and showed that it is composed of two domains with structural similarities to rhamnose-binding lectins. We identified the RH5 binding site on P113 by using a combination of hydrogen-deuterium exchange mass spectrometry and site-directed mutagenesis. We found that a monoclonal antibody to P113 that bound to this interface and inhibited the RH5-P113 interaction did not inhibit parasite blood-stage growth. These findings provide further structural information on the protein interactions of RH5 and will be helpful in guiding the development of blood-stage malaria vaccines that target RH5.
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Oct 2020
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I03-Macromolecular Crystallography
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Olivia J. S.
Macleod
,
Jean-Mathieu
Bart
,
Paula
Macgregor
,
Lori
Peacock
,
Nicholas J.
Savill
,
Svenja
Hester
,
Sophie
Ravel
,
Jack D.
Sunter
,
Camilla
Trevor
,
Steven
Rust
,
Tristan J.
Vaughan
,
Ralph
Minter
,
Shabaz
Mohammed
,
Wendy
Gibson
,
Martin C.
Taylor
,
Matthew
Higgins
,
Mark
Carrington
Diamond Proposal Number(s):
[18069]
Open Access
Abstract: Persistent pathogens have evolved to avoid elimination by the mammalian immune system including mechanisms to evade complement. Infections with African trypanosomes can persist for years and cause human and animal disease throughout sub-Saharan Africa. It is not known how trypanosomes limit the action of the alternative complement pathway. Here we identify an African trypanosome receptor for mammalian factor H, a negative regulator of the alternative pathway. Structural studies show how the receptor binds ligand, leaving inhibitory domains of factor H free to inactivate complement C3b deposited on the trypanosome surface. Receptor expression is highest in developmental stages transmitted to the tsetse fly vector and those exposed to blood meals in the tsetse gut. Receptor gene deletion reduced tsetse infection, identifying this receptor as a virulence factor for transmission. This demonstrates how a pathogen evolved a molecular mechanism to increase transmission to an insect vector by exploitation of a mammalian complement regulator.
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Mar 2020
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I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[12346]
Abstract: To maintain prolonged infection of mammals, African trypanosomes have evolved remarkable surface coats and a system of antigenic variation. Within these coats are receptors for macromolecular nutrients such as transferrin. These must be accessible to their ligands but must not confer susceptibility to immunoglobulin-mediated attack. Trypanosomes have a wide host range and their receptors must also bind ligands from diverse species. To understand how these requirements are achieved, in the context of transferrin uptake, we determined the structure of a Trypanosoma brucei transferrin receptor in complex with human transferrin, showing how this heterodimeric receptor presents a large asymmetric ligand-binding platform. The trypanosome genome contains a family of around 14 transferrin receptors, which has been proposed to allow binding to transferrin from different mammalian hosts. However, we find that a single receptor can bind transferrin from a broad range of mammals, indicating that receptor variation is unlikely to be necessary for promiscuity of host infection. In contrast, polymorphic sites and N-linked glycans are preferentially found in exposed positions on the receptor surface, not contacting transferrin, suggesting that transferrin receptor diversification is driven by a need for antigenic variation in the receptor to prolong survival in a host.
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Oct 2019
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B21-High Throughput SAXS
I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Open Access
Abstract: A major determinant of pathogenicity in malaria caused by Plasmodium falciparum is the adhesion of parasite-infected erythrocytes to the vasculature or tissues of infected individuals. This occludes blood flow, leads to inflammation, and increases parasitemia by reducing spleen-mediated clearance of the parasite. This adhesion is mediated by PfEMP1, a multivariant family of around 60 proteins per parasite genome which interact with specific host receptors. One of the most common of these receptors is intracellular adhesion molecule-1 (ICAM-1), which is bound by 2 distinct groups of PfEMP1, A-type and B or C (BC)-type. Here, we present the structure of a domain from a B-type PfEMP1 bound to ICAM-1, revealing a complex binding site. Comparison with the existing structure of an A-type PfEMP1 bound to ICAM-1 shows that the 2 complexes share a globally similar architecture. However, while the A-type PfEMP1 bind ICAM-1 through a highly conserved binding surface, the BC-type PfEMP1 use a binding site that is more diverse in sequence, similar to how PfEMP1 interact with other human receptors. We also show that A- and BC-type PfEMP1 present ICAM-1 at different angles, perhaps influencing the ability of neighboring PfEMP1 domains to bind additional receptors. This illustrates the deep diversity of the PfEMP1 and demonstrates how variations in a single domain architecture can modulate binding to a specific ligand to control function and facilitate immune evasion.
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Sep 2019
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
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Daniel G. W.
Alanine
,
Doris
Quinkert
,
Rasika
Kumarasingha
,
Shahid
Mehmood
,
Francesca R.
Donnellan
,
Nana K.
Minkah
,
Bernadeta
Dadonaite
,
Ababacar
Diouf
,
Francis
Galaway
,
Sarah E.
Silk
,
Abhishek
Jamwal
,
Jennifer M.
Marshall
,
Kazutoyo
Miura
,
Lander
Foquet
,
Sean C.
Elias
,
Geneviève M.
Labbé
,
Alexander D.
Douglas
,
Jing
Jin
,
Ruth O.
Payne
,
Joseph J.
Illingworth
,
David J.
Pattinson
,
David
Pulido
,
Barnabas G.
Williams
,
Willem A.
De Jongh
,
Gavin J.
Wright
,
Stefan H. I.
Kappe
,
Carol V.
Robinson
,
Carole A.
Long
,
Brendan S.
Crabb
,
Paul R.
Gilson
,
Matthew
Higgins
,
Simon J.
Draper
Diamond Proposal Number(s):
[18069]
Open Access
Abstract: The Plasmodium falciparum reticulocyte-binding protein homolog 5 (PfRH5) is the leading target for next-generation vaccines against the disease-causing blood-stage of malaria. However, little is known about how human antibodies confer functional immunity against this antigen. We isolated a panel of human monoclonal antibodies (mAbs) against PfRH5 from peripheral blood B cells from vaccinees in the first clinical trial of a PfRH5-based vaccine. We identified a subset of mAbs with neutralizing activity that bind to three distinct sites and another subset of mAbs that are non-functional, or even antagonistic to neutralizing antibodies. We also identify the epitope of a novel group of non-neutralizing antibodies that significantly reduce the speed of red blood cell invasion by the merozoite, thereby potentiating the effect of all neutralizing PfRH5 antibodies as well as synergizing with antibodies targeting other malaria invasion proteins. Our results provide a roadmap for structure-guided vaccine development to maximize antibody efficacy against blood-stage malaria.
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Jun 2019
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I03-Macromolecular Crystallography
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Thomas. A.
Rawlinson
,
Natalie M.
Barber
,
Franziska
Mohring
,
Jee Sun
Cho
,
Varakorn
Kosaisavee
,
Samuel F.
Gerard
,
Daniel G. W.
Alanine
,
Geneviève M.
Labbé
,
Sean C.
Elias
,
Sarah E.
Silk
,
Doris
Quinkert
,
Jing
Jin
,
Jennifer M.
Marshall
,
Ruth O.
Payne
,
Angela M.
Minassian
,
Bruce
Russell
,
Laurent
Rénia
,
François H.
Nosten
,
Robert W.
Moon
,
Matthew K.
Higgins
,
Simon J.
Draper
Diamond Proposal Number(s):
[18069]
Abstract: The most widespread form of malaria is caused by Plasmodium vivax. To replicate, this parasite must invade immature red blood cells through a process requiring interaction of the P. vivax Duffy binding protein (PvDBP) with its human receptor, the Duffy antigen receptor for chemokines. Naturally acquired antibodies that inhibit this interaction associate with clinical immunity, suggesting PvDBP as a leading candidate for inclusion in a vaccine to prevent malaria due to P. vivax. Here, we isolated a panel of monoclonal antibodies from human volunteers immunized in a clinical vaccine trial of PvDBP. We screened their ability to prevent PvDBP from binding to the Duffy antigen receptor for chemokines, and their capacity to block red blood cell invasion by a transgenic Plasmodium knowlesi parasite genetically modified to express PvDBP and to prevent reticulocyte invasion by multiple clinical isolates of P. vivax. This identified a broadly neutralizing human monoclonal antibody that inhibited invasion of all tested strains of P. vivax. Finally, we determined the structure of a complex of this antibody bound to PvDBP, indicating the molecular basis for inhibition. These findings will guide future vaccine design strategies and open up possibilities for testing the prophylactic use of such an antibody.
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May 2019
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I03-Macromolecular Crystallography
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Frank
Lennartz
,
Florian
Brod
,
Rebecca
Dabbs
,
Kazutoyo
Miura
,
David
Mekhaiel
,
Arianna
Marini
,
Matthijs
Jore
,
Max M.
Søgaard
,
Thomas
Jørgensen
,
Willem A.
De Jongh
,
Robert W.
Sauerwein
,
Carole A.
Long
,
Sumi
Biswas
,
Matthew
Higgins
Diamond Proposal Number(s):
[18069]
Open Access
Abstract: The quest to develop an effective malaria vaccine remains a major priority in the fight against global infectious disease. An approach with great potential is a transmission-blocking vaccine which induces antibodies that prevent establishment of a productive infection in mosquitos that feed on infected humans, thereby stopping the transmission cycle. One of the most promising targets for such a vaccine is the gamete surface protein, Pfs48/45. Here we establish a system for production of full-length Pfs48/45 and use this to raise a panel of monoclonal antibodies. We map the binding regions of these antibodies on Pfs48/45 and correlate the location of their epitopes with their transmission-blocking activity. Finally, we present the structure of the C-terminal domain of Pfs48/45 bound to the most potent transmission-blocking antibody, and provide key molecular information for future structure-guided immunogen design.
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Sep 2018
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I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[12346]
Abstract: Only two trypanosome subspecies are able to cause human African trypanosomiasis. To establish an infection in human blood, they must overcome the innate immune system by resisting the toxic effects of trypanolytic factor 1 and trypanolytic factor 2 (refs. 1,2). These lipoprotein complexes contain an active, pore-forming component, apolipoprotein L1 (ApoL1), that causes trypanosome cell death3. One of the two human-infective subspecies, Trypanosoma brucei rhodesiense, differs from non-infective trypanosomes solely by the presence of the serum resistance-associated protein, which binds directly to ApoL1 and blocks its pore-forming capacity3,4,5. Since this interaction is the single critical event that renders T. b. rhodesiense human- infective, detailed structural information that allows identification of binding determinants is crucial to understand immune escape by the parasite. Here, we present the structure of serum resistance-associated protein and reveal the adaptations that occurred as it diverged from other trypanosome surface molecules to neutralize ApoL1. We also present our mapping of residues important for ApoL1 binding, giving molecular insight into this interaction at the heart of human sleeping sickness.
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Jan 2018
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