The parasitophorous vacuole of the blood-stage malaria parasite

Decoding the Arsenal: Protist Effectors and Their Impact on Photosynthetic Hosts

Interactions between various microbial pathogens including viruses, bacteria, fungi, oomycetes, and their plant hosts have traditionally been the focus of phytopathology. In recent years, a significant and growing interest in the study of eukaryotic microorganisms not classified among fungi or oomycetes has emerged. Many of these protists establish complex interactions with photosynthetic hosts, and understanding these interactions is crucial in understanding the dynamics of these parasites within traditional and emerging types of farming, including marine aquaculture. Many phytopathogenic protists are biotrophs with complex polyphasic life cycles, which makes them difficult or impossible to culture, a fact reflected in a wide gap in the availability of comprehensive genomic data when compared to fungal and oomycete plant pathogens. Furthermore, our ability to use available genomic resources for these protists is limited by the broad taxonomic distance that these organisms span, which makes comparisons with other genomic datasets difficult. The current rapid progress in genomics and computational tools for the prediction of protein functions and interactions is revolutionizing the landscape in plant pathology. This is also opening novel possibilities, specifically for a deeper understanding of protist effectors. Tools like AlphaFold2 enable structure-based function prediction of effector candidates with divergent protein sequences. In turn, this allows us to ask better biological questions and, coupled with innovative experimental strategies, will lead into a new era of effector research, especially for protists, to expand our knowledge on these elusive pathogens and their interactions with photosynthetic hosts. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

PEXEL is a proteolytic maturation site for both exported and non-exported Plasmodium proteins

Obligate intracellular malaria parasites dramatically remodel their erythrocyte host through effector protein export to create a niche for survival. Most exported proteins contain a pentameric Plasmodium export element (PEXEL)/host-targeting motif that is cleaved in the parasite ER by the aspartic protease Plasmepsin V (PMV). This processing event exposes a mature N terminus required for translocation into the host cell and is not known to occur in non-exported proteins. Here, we report that the non-exported parasitophorous vacuole protein UIS2 contains a bona fide PEXEL motif that is processed in the P. falciparum blood stage. While the N termini of exported proteins containing the PEXEL and immediately downstream ~10 residues are sufficient to mediate translocation into the RBC, the equivalent UIS2 N terminus does not promote the export of a reporter. Curiously, the UIS2 PEXEL contains an unusual aspartic acid at the fourth position, which constitutes the extreme N-terminal residue following PEXEL cleavage (P1', RIL↓DE). Using a series of chimeric reporter fusions, we show that Asp at P1' is permissive for PMV processing but abrogates export. Moreover, mutation of this single UIS2 residue to alanine enables export, reinforcing that the mature N terminus mediates export, not PEXEL processing per se. Prompted by this observation, we further show that PEXEL sequences in the N termini of other non-exported rhoptry proteins are also processed, suggesting that PMV may be a more general secretory maturase than previously appreciated, similar to orthologs in related apicomplexans. Our findings provide new insight into the unique N-terminal constraints that mark proteins for export.IMPORTANCEHost erythrocyte remodeling by malaria parasite-exported effector proteins is critical to parasite survival and disease pathogenesis. In the deadliest malaria parasite Plasmodium falciparum, most exported proteins undergo proteolytic maturation via recognition of the pentameric Plasmodium export element (PEXEL)/host-targeting motif by the aspartic protease Plasmepsin V, which exposes a mature N terminus that is conducive for export into the erythrocyte host cell. While PEXEL processing is considered a unique mark of exported proteins, we demonstrate that PEXEL motifs are present and processed in non-exported proteins. Importantly, we show that specific residues at the variable fourth position of the PEXEL motif inhibit export despite being permissive for processing, reinforcing that features of the mature N terminus, and not PEXEL cleavage, identify cargo for export. This opens the door to further inquiry into the nature and evolution of the PEXEL motif.

Single-cell quantitative bioimaging of P. berghei liver stage translation

IMPORTANCE

Plasmodium parasites cause malaria in humans. New multistage active antimalarial drugs are needed, and a promising class of drugs targets the core cellular process of translation, which has many potential molecular targets. During the obligate liver stage, Plasmodium parasites grow in metabolically active hepatocytes, making it challenging to study core cellular processes common to both host cells and parasites, as the signal from the host typically overwhelms that of the parasite. Here, we present and validate a flexible assay to quantify Plasmodium liver stage translation using a technique to fluorescently label the newly synthesized proteins of both host and parasite followed by computational separation of their respective nascent proteomes in confocal image sets. We use the assay to determine whether a test set of known compounds are direct or indirect liver stage translation inhibitors and show that the assay can also predict the mode of action for novel antimalarial compounds.

Bionanotechnology and bioMEMS (BNM): state-of-the-art applications, opportunities, and challenges

The development of micro- and nanotechnology for biomedical applications has defined the cutting edge of medical technology for over three decades, as advancements in fabrication technology developed originally in the semiconductor industry have been applied to solving ever-more complex problems in medicine and biology. These technologies are ideally suited to interfacing with life sciences, since they are on the scale lengths as cells (microns) and biomacromolecules (nanometers). In this paper, we review the state of the art in bionanotechnology and bioMEMS (collectively BNM), including developments and challenges in the areas of BNM, such as microfluidic organ-on-chip devices, oral drug delivery, emerging technologies for managing infectious diseases, 3D printed microfluidic devices, AC electrokinetics, flexible MEMS devices, implantable microdevices, paper-based microfluidic platforms for cellular analysis, and wearable sensors for point-of-care testing.

PEXEL is a proteolytic maturation site for both exported and non-exported Plasmodium proteins

Obligate intracellular malaria parasites dramatically remodel their erythrocyte host through effector protein export to create a niche for survival. Most exported proteins contain a pentameric P lasmodium ex port el ement (PEXEL)/Host Targeting Motif that is cleaved in the parasite ER by the aspartic protease Plasmepsin V (PMV). This processing event exposes a mature N-terminus required for translocation into the host cell and is not known to occur in non-exported proteins. Here we report that the non-exported parasitophorous vacuole protein UIS2 contains a bona fide PEXEL motif that is processed in the P. falciparum blood-stage. While the N-termini of exported proteins containing the PEXEL and immediately downstream ∼10 residues is sufficient to mediate translocation into the RBC, the equivalent UIS2 N-terminus does not promote export of a reporter. Curiously, the UIS2 PEXEL contains an unusual aspartic acid at the fourth position which constitutes the extreme N-terminal residue following PEXEL cleavage (P1', RILτDE). Using a series of chimeric reporter fusions, we show that Asp at P1' is permissive for PMV processing but abrogates export. Moreover, mutation of this single UIS2 residue to alanine enables export, reinforcing that the mature N-terminus mediates export, not PEXEL processing per se . Prompted by this observation, we further show that PEXEL sequences in the N-termini of other non-exported rhoptry proteins are also processed, suggesting that PMV may be a more general secretory maturase than previously appreciated, similar to orthologs in related apicomplexans. Our findings provide new insight into the unique N-terminal constraints that mark proteins for export.

Importance

Host erythrocyte remodeling by malaria parasite exported effector proteins is critical to parasite survival and disease pathogenesis. In the deadliest malaria parasite Plasmodium falciparum , most exported proteins undergo proteolytic maturation via recognition of the pentameric P lasmodium ex port el ement (PEXEL)/Host Targeting motif by the aspartic protease Plasmepsin V (PMV) which exposes a mature N-terminus that is conducive for export into the erythrocyte host cell. While PEXEL processing is considered a unique mark of exported proteins, we demonstrate PEXEL motifs are present and processed in non-exported proteins. Importantly, we show that specific residues at the variable fourth position of the PEXEL motif inhibit export despite being permissive for processing by PMV, reinforcing that features of the mature N-terminus, and not PEXEL cleavage, identify cargo for export cargo. This opens the door to further inquiry into the nature and evolution of the PEXEL motif.

Single-cell quantitative bioimaging of P. berghei liver stage translation

Plasmodium parasite resistance to existing antimalarial drugs poses a devastating threat to the lives of many who depend on their efficacy. New antimalarial drugs and novel drug targets are in critical need, along with novel assays to accelerate their identification. Given the essentiality of protein synthesis throughout the complex parasite lifecycle, translation inhibitors are a promising drug class, capable of targeting the disease-causing blood stage of infection, as well as the asymptomatic liver stage, a crucial target for prophylaxis. To identify compounds capable of inhibiting liver stage parasite translation, we developed an assay to visualize and quantify translation in the P. berghei-HepG2 infection model. After labeling infected monolayers with o-propargyl puromycin (OPP), a functionalized analog of puromycin permitting subsequent bioorthogonal addition of a fluorophore to each OPP-terminated nascent polypetide, we use automated confocal feedback microscopy followed by batch image segmentation and feature extraction to visualize and quantify the nascent proteome in individual P. berghei liver stage parasites and host cells simultaneously. After validation, we demonstrate specific, concentration-dependent liver stage translation inhibition by both parasite-selective and pan-eukaryotic active compounds, and further show that acute pre-treatment and competition modes of the OPP assay can distinguish between direct and indirect translation inhibitors. We identify a Malaria Box compound, MMV019266, as a direct translation inhibitor in P. berghei liver stages and confirm this potential mode of action in P. falciparum asexual blood stages.

Knobs, Adhesion, and Severe Falciparum Malaria

Plasmodium falciparum can cause a severe disease with high mortality. A major factor contributing to the increased virulence of P. falciparum, as compared to other human malarial parasites, is the sequestration of infected erythrocytes in the capillary beds of organs and tissues. This sequestration is due to the cytoadherence of infected erythrocytes to endothelial cells. Cytoadherence is primarily mediated by a parasite protein expressed on the surface of the infected erythrocyte called P. falciparum erythrocyte membrane protein-1 (PfEMP1). PfEMP1 is embedded in electron-dense protuberances on the surface of the infected erythrocytes called knobs. These knobs are assembled on the erythrocyte membrane via exported parasite proteins, and the knobs function as focal points for the cytoadherence of infected erythrocytes to endothelial cells. PfEMP1 is a member of the var gene family, and there are approximately 60 antigenically distinct PfEMP1 alleles per parasite genome. Var gene expression exhibits allelic exclusion, with only a single allele being expressed by an individual parasite. This results in sequential waves of antigenically distinct infected erythrocytes and this antigenic variation allows the parasite to establish long-term chronic infections. A wide range of endothelial cell receptors can bind to the various PfEMP1 alleles, and thus, antigenic variation also results in a change in the cytoadherence phenotype. The cytoadherence phenotype may result in infected erythrocytes sequestering in different tissues and this difference in sequestration may explain the wide range of possible clinical manifestations associated with severe falciparum malaria.

Phagocytosis underpins the biotrophic lifestyle of intracellular parasites in the class Phytomyxea (Rhizaria)

Phytomyxea are intracellular biotrophic parasites infecting plants and stramenopiles, including the agriculturally impactful Plasmodiophora brassicae and the brown seaweed pathogen Maullinia ectocarpii. They belong to the clade Rhizaria, where phagotrophy is the main mode of nutrition. Phagocytosis is a complex trait of eukaryotes, well documented for free-living unicellular eukaryotes and specific cellular types of animals. Data on phagocytosis in intracellular, biotrophic parasites are scant. Phagocytosis, where parts of the host cell are consumed at once, is seemingly at odds with intracellular biotrophy. Here we provide evidence that phagotrophy is part of the nutritional strategy of Phytomyxea, using morphological and genetic data (including a novel transcriptome of M. ectocarpii). We document intracellular phagocytosis in P. brassicae and M. ectocarpii by transmission electron microscopy and fluorescent in situ hybridization. Our investigations confirm molecular signatures of phagocytosis in Phytomyxea and hint at a small specialized subset of genes used for intracellular phagocytosis. Microscopic evidence confirms the existence of intracellular phagocytosis, which in Phytomyxea targets primarily host organelles. Phagocytosis seems to coexist with the manipulation of host physiology typical of biotrophic interactions. Our findings resolve long debated questions on the feeding behaviour of Phytomyxea, suggesting an unrecognized role for phagocytosis in biotrophic interactions.

Plasmodium parasitophorous vacuole membrane protein Pfs16 promotes malaria transmission by silencing mosquito immunity

With rising cases for the first time in years, malaria remains a significant public health burden. The sexual stage of the malaria parasite infects mosquitoes to transmit malaria from host to host. Hence, an infected mosquito plays an essential role in malaria transmission. Plasmodium falciparum is the most dominant and dangerous malaria pathogen. Previous studies identified a sexual stage-specific protein 16 (Pfs16) localized to the parasitophorous vacuole membrane (PVM). Here we elucidate the function of Pfs16 during malaria transmission. Our structural analysis identified Pfs16 as an alpha-helical integral membrane protein with one transmembrane domain connecting to two regions across PVM. ELISA assays showed that insect cell-expressed recombinant Pfs16 (rPfs16) interacted with An. gambiae midguts, and microscopy found that rPfs16 bound to midgut epithelial cells. Transmission-blocking assays demonstrated that polyclonal antibodies against Pfs16 significantly reduced the number of oocysts in mosquito midguts. However, on the contrary, feeding rPfs16 increased the number of oocysts. Further analysis revealed that Pfs16 reduced the activity of mosquito midgut caspase 3/7, a key enzyme in the mosquito Jun-N-terminal kinase (JNK) immune pathway. We conclude that Pfs16 facilitates parasites to invade mosquito midguts by actively silencing the mosquito's innate immunity through its interaction with the midgut epithelial cells. Therefore, Pfs16 is a potential target to control malaria transmission.

The enemy within: lipid asymmetry in intracellular parasite-host interactions

Eukaryotic pathogens with an intracellular parasitic lifestyle are shielded from extracellular threats during replication and growth. In addition to many nutrients, parasites scavenge host cell lipids to establish complex membrane structures inside their host cells. To counteract the disturbance of the host cell plasma membrane they have evolved strategies to regulate phospholipid asymmetry. In this review, the function and importance of lipid asymmetry in the interactions of intracellular protozoan parasites with the target and immune cells of the host are highlighted. The malaria parasite Plasmodium infects red blood cells and extensively refurbishes these terminally differentiated cells. Cholesterol depletion and an altered intracellular calcium ion homeostasis can lead to disruption in erythrocyte membrane asymmetry and increased exposure of phosphatidylserine (PS). Binding to the PS receptor on monocytes and macrophages results in phagocytosis and destruction of infected erythrocytes. Leishmania parasites display apoptotic mimicry by actively enhancing PS exposure on their surface to trigger increased infection of macrophages. In extracellular Toxoplasma gondii a P4-type ATPase/CDC50 co-chaperone pair functions as a flippase important for exocytosis of specialised secretory organelles. Identification and functional analysis of parasite lipid-translocating proteins, i.e. flippases, floppases, and scramblases, will be central for the recognition of the molecular mechanisms of parasite/host interactions. Ultimately, a better understanding of parasitic diseases, host immunity, and immune escape by parasites require more research on the dynamics of phospholipid bilayers of parasites and the infected host cell.

Optical diffraction tomography and image reconstruction to measure host cell alterations caused by divergent Plasmodium species

Malaria is a life-threatening infectious disease caused by parasites of the genus Plasmodium. Understanding the biological features of various parasite forms is important for the optical diagnosis and defining pathological states, which are often constrained by the lack of ambient visualization approaches. Here, we employ a label-free tomographic technique to visualize the host red blood cell (RBC) remodeling process and quantify changes in biochemical properties arising from parasitization. Through this, we provide a quantitative body of information pertaining to the influence of host cell environment on growth, survival, and replication of P. falciparum and P. vivax in their respective host cells: mature erythrocytes and young reticulocytes. These exquisite three-dimensional measurements of infected red cells demonstrats the potential of evolving 3D imaging to advance our understanding of Plasmodium biology and host-parasite interactions.

The PTEX Pore Component EXP2 Is Important for Intrahepatic Development during the Plasmodium Liver Stage

During vertebrate infection, obligate intracellular malaria parasites develop within a parasitophorous vacuole, which constitutes the interface between the parasite and its hepatocyte or erythrocyte host cells. To traverse this barrier, Plasmodium spp. utilize a dual-function pore formed by EXP2 for nutrient transport and, in the context of the PTEX translocon, effector protein export across the vacuole membrane. While critical to blood-stage survival, less is known about EXP2/PTEX function in the liver stage, although major differences in the export mechanism are suggested by absence of the PTEX unfoldase HSP101 in the intrahepatic vacuole. Here, we employed the glucosamine-activated glmS ribozyme to study the role of EXP2 during Plasmodium berghei liver-stage development in hepatoma cells. Insertion of the glmS sequence into the exp2 3' untranslated region (UTR) enabled glucosamine-dependent depletion of EXP2 after hepatocyte invasion, allowing separation of EXP2 function during intrahepatic development from a recently reported role in hepatocyte invasion. Postinvasion EXP2 knockdown reduced parasite size and largely abolished expression of the mid- to late-liver-stage marker LISP2. As an orthogonal approach to monitor development, EXP2-glmS parasites and controls were engineered to express nanoluciferase. Activation of glmS after invasion substantially decreased luminescence in hepatoma monolayers and in culture supernatants at later time points corresponding to merosome detachment, which marks the culmination of liver-stage development. Collectively, our findings extend the utility of the glmS ribozyme to study protein function in the liver stage and reveal that EXP2 is important for intrahepatic parasite development, indicating that PTEX components also function at the hepatocyte-parasite interface. IMPORTANCE After the mosquito bite that initiates a Plasmodium infection, parasites first travel to the liver and develop in hepatocytes. This liver stage is asymptomatic but necessary for the parasite to transition to the merozoite form, which infects red blood cells and causes malaria. To take over their host cells, avoid immune defenses, and fuel their growth, these obligately intracellular parasites must import nutrients and export effector proteins across a vacuole membrane in which they reside. In the blood stage, these processes depend on a translocon called PTEX, but it is unclear if PTEX also functions during the liver stage. Here, we adapted the glmS ribozyme to control expression of EXP2, the membrane pore component of PTEX, during the liver stage of the rodent malaria parasite Plasmodium berghei. Our results show that EXP2 is important for intracellular development in the hepatocyte, revealing that PTEX components are also functionally important during liver-stage infection.

Computational Clues of Immunogenic Hotspots in Plasmodium falciparum Erythrocytic Stage Vaccine Candidate Antigens: In Silico Approach

Malaria is the most pernicious parasitic infection, and Plasmodium falciparum is the most virulent species with substantial morbidity and mortality worldwide. The present in silico investigation was performed to reveal the biophysical characteristics and immunogenic epitopes of the 14 blood-stage proteins of the P. falciparum using comprehensive immunoinformatics approaches. For this aim, various web servers were employed to predict subcellular localization, antigenicity, allergenicity, solubility, physicochemical properties, posttranslational modification sites (PTMs), the presence of signal peptide, and transmembrane domains. Moreover, structural analysis for secondary and 3D model predictions were performed for all and stable proteins, respectively. Finally, human helper T lymphocyte (HTL) epitopes were predicted using HLA reference set of IEDB server and screened in terms of antigenicity, allergenicity, and IFN-γ induction as well as population coverage. Also, a multiserver B-cell epitope prediction was done with subsequent screening for antigenicity, allergenicity, and solubility. Altogether, these proteins showed appropriate antigenicity, abundant PTMs, and many B-cell and HTL epitopes, which could be directed for future vaccination studies in the context of multiepitope vaccine design.

PfMDR1 Transport Rates Assessed in Intact Isolated Plasmodium falciparum Digestive Vacuoles Reflect Functional Drug Resistance Relationship with pfmdr1 Mutations

Drug resistance often emerges from mutations in solute transporters. Single amino acid exchanges may alter functionality of transporters with ‘de novo’ ability to transport drugs away from their site of action. The PfMDR1 transporter (or P-glycoprotein 1) is located in the membrane of the digestive vacuole (DV), functions as an ATP-dependent pump, and transports substrates into the DV. In this study, four strains of Plasmodium falciparum, carrying various pfmdr1 gene mutations, were analysed for their transport characteristics of Fluo-4 in isolated DVs of parasites. To obtain quantitative estimates for PfMDR1 DV surface expression, PfMDR1 protein amounts on each strain’s DV membrane were evaluated by quantitative ELISA. Fluo-4, acting as a substrate for PfMDR1, was applied in DV uptake assays (‘reverse Ca²⁺ imaging’). Viable DVs were isolated from trophozoite stages with preserved PfMDR1 activity. This newly developed assay enabled us to measure the number of Fluo-4 molecules actively transported into isolated DVs per PfMDR1 molecule. The drug-resistant strain Dd2 presented the highest transport rates, followed by K1 and the drug-sensitive strain 3D7, compatible with their copy numbers. With this assay, an evaluation of the probability of resistance formation for newly developed drugs can be implemented in early stages of drug development.

Functional Analysis of the Expanded Phosphodiesterase Gene Family in Toxoplasma gondii Tachyzoites

Toxoplasma motility is both activated and suppressed by 3′,5′-cyclic nucleotide signaling. Cyclic GMP (cGMP) signaling through Toxoplasma gondii protein kinase G (TgPKG) activates motility, whereas cyclic AMP (cAMP) signaling through TgPKAc1 inhibits motility. Despite their importance, it remains unclear how cGMP and cAMP levels are maintained in Toxoplasma. Phosphodiesterases (PDEs) are known to inactivate cyclic nucleotides and are highly expanded in the Toxoplasma genome. Here, we analyzed the expression and function of the 18-member TgPDE family in tachyzoites, the virulent life stage of Toxoplasma. We detected the expression of 11 of 18 TgPDEs, confirming prior expression studies. A knockdown screen of the TgPDE family revealed four TgPDEs that contribute to lytic Toxoplasma growth (TgPDE1, TgPDE2, TgPDE5, and TgPDE9). Depletion of TgPDE1 or TgPDE2 caused severe growth defects, prompting further investigation. While TgPDE1 was important for extracellular motility, TgPDE2 was important for host cell invasion, parasite replication, host cell egress, and extracellular motility. TgPDE1 displayed a plasma membrane/cytomembranous distribution, whereas TgPDE2 displayed an endoplasmic reticulum/cytomembranous distribution. Biochemical analysis of TgPDE1 and TgPDE2 purified from Toxoplasma lysates revealed that TgPDE1 hydrolyzes both cGMP and cAMP, whereas TgPDE2 was cAMP specific. Interactome studies of TgPDE1 and TgPDE2 indicated that they do not physically interact with each other or other TgPDEs but may be regulated by kinases and proteases. Our studies have identified TgPDE1 and TgPDE2 as central regulators of tachyzoite cyclic nucleotide levels and enable future studies aimed at determining how these enzymes are regulated and cooperate to control Toxoplasma motility and growth.

IMPORTANCE Apicomplexan parasites require motility to actively infect host cells and cause disease. Cyclic nucleotide signaling governs apicomplexan motility, but it is unclear how cyclic nucleotide levels are maintained in these parasites. In search of novel regulators of cyclic nucleotides in the model apicomplexan Toxoplasma, we identified and characterized two catalytically active phosphodiesterases, TgPDE1 and TgPDE2, that are important for Toxoplasma’s virulent tachyzoite life cycle. Enzymes that generate, sense, or degrade cyclic nucleotides make attractive targets for therapies aimed at paralyzing and killing apicomplexan parasites.

AGIA Tag System for Ultrastructural Protein Localization Analysis in Blood-Stage Plasmodium falciparum

Precise subcellular localization of proteins is the key to elucidating the physiological role of these molecules in malaria parasite development, understanding of pathogenesis, and protective immunity. In Plasmodium falciparum, however, detection of proteins in the blood-stage parasites is greatly hampered by the lack of versatile protein tags which can intrinsically label such molecules. Thus, in this study, to develop a novel system that can be used to evaluate subcellular localization of known and novel proteins, we assessed the application of AGIA tag, consisting of 9 amino acids (EEAAGIARP), in P. falciparum blood-stage parasites. Specifically, AGIA-tagged ring-infected erythrocyte surface antigen (RESA-AGIA) was episomally expressed in P. falciparum 3D7 strain. The RESA-AGIA protein was detected by Western blotting and immunofluorescence assay (IFA) using recombinant rabbit anti-AGIA tag monoclonal antibody (mAb) with a high signal/noise ratio. Similarly, AGIA-tagged multidrug resistance protein 1 (MDR1-AGIA), as an example of polyptic transmembrane protein, was endogenously expressed and detected by Western blotting and IFA with anti-AGIA tag mAb. Immunoelectron microscopy of the RESA-AGIA transfected merozoites revealed that mouse anti-RESA and the rabbit anti-AGIA mAb signals could definitively co-localize to the dense granules. Put together, this study demonstrates AGIA tag/anti-AGIA rabbit mAb system as a potentially useful tool for elucidating the subcellular localization of new and understudied proteins in blood-stage malaria parasites at the nanometer-level resolution.

Pantothenate and CoA biosynthesis in Apicomplexa and their promise as antiparasitic drug targets

The Apicomplexa phylum comprises thousands of distinct intracellular parasite species, including coccidians, haemosporidians, piroplasms, and cryptosporidia. These parasites are characterized by complex and divergent life cycles occupying a variety of host niches. Consequently, they exhibit distinct adaptations to the differences in nutritional availabilities, either relying on biosynthetic pathways or by salvaging metabolites from their host. Pantothenate (Pan, vitamin B5) is the precursor for the synthesis of an essential cofactor, coenzyme A (CoA), but among the apicomplexans, only the coccidian subgroup has the ability to synthesize Pan. While the pathway to synthesize CoA from Pan is largely conserved across all branches of life, there are differences in the redundancy of enzymes and possible alternative pathways to generate CoA from Pan. Impeding the scavenge of Pan and synthesis of Pan and CoA have been long recognized as potential targets for antimicrobial drug development, but in order to fully exploit these critical pathways, it is important to understand such differences. Recently, a potent class of pantothenamides (PanAms), Pan analogs, which target CoA-utilizing enzymes, has entered antimalarial preclinical development. The potential of PanAms to target multiple downstream pathways make them a promising compound class as broad antiparasitic drugs against other apicomplexans. In this review, we summarize the recent advances in understanding the Pan and CoA biosynthesis pathways, and the suitability of these pathways as drug targets in Apicomplexa, with a particular focus on the cyst-forming coccidian, Toxoplasma gondii, and the haemosporidian, Plasmodium falciparum.

Structured to conquer: transport across the Plasmodium parasitophorous vacuole

During the vertebrate stage of the Plasmodium life cycle, obligate intracellular malaria parasites establish a vacuolar niche for replication, first within host hepatocytes at the pre-patent liver-stage and subsequently in erythrocytes during the pathogenic blood-stage. Survival in this protective microenvironment requires diverse transport mechanisms that enable the parasite to transcend the vacuolar barrier. Effector proteins exported out of the vacuole modify the erythrocyte membrane, increasing access to serum nutrients which then cross the vacuole membrane through a nutrient-permeable channel, supporting rapid parasite growth. This review highlights the most recent insights into the organization of the parasite vacuole to facilitate the solute, lipid and effector protein trafficking that establishes a nutrition pipeline in the terminally differentiated, organelle-free red blood cell.

Plasmepsin-like Aspartyl Proteases in Babesia

Apicomplexan genomes encode multiple pepsin-family aspartyl proteases (APs) that phylogenetically cluster to six independent clades (A to F). Such diversification has been powered by the function-driven evolution of the ancestral apicomplexan AP gene and is associated with the adaptation of various apicomplexan species to different strategies of host infection and transmission through various invertebrate vectors. To estimate the potential roles of Babesia APs, we performed qRT-PCR-based expressional profiling of Babesia microti APs (BmASP2, 3, 5, 6), which revealed the dynamically changing mRNA levels and indicated the specific roles of individual BmASP isoenzymes throughout the life cycle of this parasite. To expand on the current knowledge on piroplasmid APs, we searched the EuPathDB and NCBI GenBank databases to identify and phylogenetically analyse the complete sets of APs encoded by the genomes of selected Babesia and Theileria species. Our results clearly determine the potential roles of identified APs by their phylogenetic relation to their homologues of known function—Plasmodium falciparum plasmepsins (PfPM I–X) and Toxoplasma gondii aspartyl proteases (TgASP1–7). Due to the analogies with plasmodial plasmepsins, piroplasmid APs represent valuable enzymatic targets that are druggable by small molecule inhibitors—candidate molecules for the yet-missing specific therapy for babesiosis.

Lipid transport proteins in malaria, from Plasmodium parasites to their hosts

Eukaryotic unicellular pathogens from the genus Plasmodium are the etiological agents of malaria, a disease that persists over a wide range of vertebrate species, including humans. During its dynamic lifecycle, survival in the different hosts depends on the parasite's ability to establish a suitable environmental milieu. To achieve this, specific host processes are exploited to support optimal growth, including extensive modifications to the infected host cell. These modifications include the formation of novel membranous structures, which are induced by the parasite. Consequently, to maintain a finely tuned and dynamic lipid environment, the organisation and distribution of lipids to different cell sites likely requires specialised lipid transfer proteins (LTPs). Indeed, several parasite and host-derived LTPs have been identified and shown to be essential at specific stages. Here we describe the roles of LTPs in parasite development and adaptation to its host including how the latest studies are profiting from the improved genetic, lipidomic and imaging toolkits available to study Plasmodium parasites. Lastly, a list of predicted Plasmodium LTPs is provided to encourage research in this field.

Unique Endomembrane Systems and Virulence in Pathogenic Protozoa

Virulence in pathogenic protozoa is often tied to secretory processes such as the expression of adhesins on parasite surfaces or the secretion of proteases to assisted in tissue invasion and other proteins to avoid the immune system. This review is a broad overview of the endomembrane systems of pathogenic protozoa with a focus on Giardia, Trichomonas, Entamoeba, kinetoplastids, and apicomplexans. The focus is on unique features of these protozoa and how these features relate to virulence. In general, the basic elements of the endocytic and exocytic pathways are present in all protozoa. Some of these elements, especially the endosomal compartments, have been repurposed by the various species and quite often the repurposing is associated with virulence. The Apicomplexa exhibit the most unique endomembrane systems. This includes unique secretory organelles that play a central role in interactions between parasite and host and are involved in the invasion of host cells. Furthermore, as intracellular parasites, the apicomplexans extensively modify their host cells through the secretion of proteins and other material into the host cell. This includes a unique targeting motif for proteins destined for the host cell. Most notable among the apicomplexans is the malaria parasite, which extensively modifies and exports numerous proteins into the host erythrocyte. These modifications of the host erythrocyte include the formation of unique membranes and structures in the host erythrocyte cytoplasm and on the erythrocyte membrane. The transport of parasite proteins to the host erythrocyte involves several unique mechanisms and components, as well as the generation of compartments within the erythrocyte that participate in extraparasite trafficking.

Atomic Resolution Homology Models and Molecular Dynamics Simulations of Plasmodium falciparum Tubulins

Microtubules are tubulin polymers present in the eukaryotic cytoskeleton essential for structural stability and cell division that are also roadways for intracellular transport of vesicles and organelles. In the human malaria parasite Plasmodium falciparum, apart from providing structural stability and cell division, microtubules also facilitate important biological activities crucial for parasite survival in hosts, such as egression and motility. Hence, parasite structures and processes involving microtubules are among the most important drug targets for discovering much-needed novel Plasmodium inhibitors. The current study aims to construct reliable and high-quality 3D models of α-, β-, and γ-tubulins using various modeling techniques. We identified a common binding pocket specific to Plasmodium α-, β-, and γ-tubulins. Molecular dynamics simulations confirmed the stability of the Plasmodium tubulin 3D structures. The models generated in the present study may be used for protein-protein and protein-drug interaction investigations targeted toward designing malaria parasite tubulin-specific inhibitors.

Targeting SUMOylation in Plasmodium as a Potential Target for Malaria Therapy

Malaria is a parasitic disease that represents a public health problem worldwide. Protozoans of the Plasmodium genus are responsible for causing malaria in humans. Plasmodium species have a complex life cycle that requires post-translational modifications (PTMs) to control cellular activities temporally and spatially and regulate the levels of critical proteins and cellular mechanisms for maintaining an efficient infection and immune evasion. SUMOylation is a PTM formed by the covalent linkage of a small ubiquitin-like modifier protein to the lysine residues on the protein substrate. This PTM is reversible and is triggered by the sequential action of three enzymes: E1-activating, E2-conjugating, and E3 ligase. On the other end, ubiquitin-like-protein-specific proteases in yeast and sentrin-specific proteases in mammals are responsible for processing SUMO peptides and for deconjugating SUMOylated moieties. Further studies are necessary to comprehend the molecular mechanisms and cellular functions of SUMO in Plasmodium. The emergence of drug-resistant malaria parasites prompts the discovery of new targets and antimalarial drugs with novel mechanisms of action. In this scenario, the conserved biological processes regulated by SUMOylation in the malaria parasites such as gene expression regulation, oxidative stress response, ubiquitylation, and proteasome pathways, suggest PfSUMO as a new potential drug target. This mini-review focuses on the current understanding of the mechanism of action of the PfSUMO during the coordinated multi-step life cycle of Plasmodium and discusses them as attractive new target proteins for the development of parasite-specific inhibitors and therapeutic intervention toward malaria disease.

Defining the Essential Exportome of the Malaria Parasite

To survive inside red blood cells (RBCs), malaria parasites export many proteins to alter their host cell's physiological properties. Although most proteins of this exportome are involved in immune avoidance or in the trafficking of exported proteins to the host membrane, about 20% are essential for parasite survival in culture but little is known about their biological functions. Here, we have combined information from large-scale genetic screens and targeted gene-disruption studies to tabulate all currently known Plasmodium falciparum exported proteins according to their likelihood of being essential. We also discuss the essential functional pathways that exported proteins might be involved in to help direct research efforts towards a more comprehensive understanding of host-cell remodelling.

Borgheti-Cardoso L, Albertazzi L, Dimova R, Fernàndez-Busquets X. The ESCRT-III machinery participates in the production of extracellular vesicles and protein export during Plasmodium falciparum infection

Infection with Plasmodium falciparum enhances extracellular vesicle (EV) production in parasitized red blood cells (pRBCs), an important mechanism for parasite-to-parasite communication during the asexual intraerythrocytic life cycle. The endosomal sorting complex required for transport (ESCRT), and in particular the ESCRT-III sub-complex, participates in the formation of EVs in higher eukaryotes. However, RBCs have lost the majority of their organelles through the maturation process, including an important reduction in their vesicular network. Therefore, the mechanism of EV production in P. falciparum-infected RBCs remains to be elucidated. Here we demonstrate that P. falciparum possesses a functional ESCRT-III machinery activated by an alternative recruitment pathway involving the action of PfBro1 and PfVps32/PfVps60 proteins. Additionally, multivesicular body formation and membrane shedding, both reported mechanisms of EV production, were reconstituted in the membrane model of giant unilamellar vesicles using the purified recombinant proteins. Moreover, the presence of PfVps32, PfVps60 and PfBro1 in EVs purified from a pRBC culture was confirmed by super-resolution microscopy and dot blot assays. Finally, disruption of the PfVps60 gene led to a reduction in the number of the produced EVs in the KO strain and affected the distribution of other ESCRT-III components. Overall, our results increase the knowledge on the underlying molecular mechanisms during malaria pathogenesis and demonstrate that ESCRT-III P. falciparum proteins participate in EV production.

Malaria is a disease caused by Plasmodium parasites that is still a leading cause of death in many low-income countries, and for which currently available therapeutic strategies are not succeeding in its control, let alone eradication. An interesting feature observed after Plasmodium invasion is the increase of extracellular vesicles (EVs) generated by parasitized red blood cells (pRBCs), which lack a vesicular trafficking that would explain EV production. Here, by combining different approaches, we demonstrated the participation of the endosomal sorting complex required for transport (ESCRT) machinery from Plasmodium falciparum in the production of EVs in pRBCs. Moreover, we were able to detect ESCRT-III proteins adjacent to the membrane of the host and in EVs purified from a pRBC culture, which shows the export of these proteins and their participation in EV production. Finally, the disruption of an ESCRT-III associated gene, Pfvps60, led to a significant reduction in the amount of EVs. Altogether, these results confirm ESCRT-III participation in EV production and provide novel information on the P. falciparum protein export mechanisms, which can be used for the development of new therapeutic strategies against malaria, based on the disruption of EV formation and trafficking.

Transport mechanisms at the malaria parasite-host cell interface

Obligate intracellular malaria parasites reside within a vacuolar compartment generated during invasion which is the principal interface between pathogen and host. To subvert their host cell and support their metabolism, these parasites coordinate a range of transport activities at this membrane interface that are critically important to parasite survival and virulence, including nutrient import, waste efflux, effector protein export, and uptake of host cell cytosol. Here, we review our current understanding of the transport mechanisms acting at the malaria parasite vacuole during the blood and liver-stages of development with a particular focus on recent advances in our understanding of effector protein translocation into the host cell by the Plasmodium Translocon of EXported proteins (PTEX) and small molecule transport by the PTEX membrane-spanning pore EXP2. Comparison to Toxoplasma gondii and other related apicomplexans is provided to highlight how similar and divergent mechanisms are employed to fulfill analogous transport activities.

Highlighting membrane protein structure and function: A celebration of the Protein Data Bank

Biological membranes define the boundaries of cells and compartmentalize the chemical and physical processes required for life. Many biological processes are carried out by proteins embedded in or associated with such membranes. Determination of membrane protein (MP) structures at atomic or near-atomic resolution plays a vital role in elucidating their structural and functional impact in biology. This endeavor has determined 1198 unique MP structures as of early 2021. The value of these structures is expanded greatly by deposition of their three-dimensional (3D) coordinates into the Protein Data Bank (PDB) after the first atomic MP structure was elucidated in 1985. Since then, free access to MP structures facilitates broader and deeper understanding of MPs, which provides crucial new insights into their biological functions. Here we highlight the structural and functional biology of representative MPs and landmarks in the evolution of new technologies, with insights into key developments influenced by the PDB in magnifying their impact.

Eugenol disrupts Plasmodium falciparum intracellular development during the erythrocytic cycle and protects against cerebral malaria

BACKGROUND

Malaria is a parasitic disease that compromises the human host. Currently, control of the Plasmodium falciparum burden is centered on artemisinin-based combination therapies. However, decreased sensitivity to artemisinin and derivatives has been reported, therefore it is important to identify new therapeutic strategies.

METHOD

We used human erythrocytes infected with P. falciparum and experimental cerebral malaria (ECM) animal model to assess the potential antimalarial effect of eugenol, a component of clove bud essential oil.

RESULTS

Plasmodium falciparum cultures treated with increasing concentrations of eugenol reduced parasitemia in a dose-dependent manner, with IC₅₀ of 532.42 ± 29.55 μM. This effect seems to be irreversible and maintained even in the presence of high parasitemia. The prominent effect of eugenol was detected in the evolution from schizont to ring forms, inducing important morphological changes, indicating a disruption in the development of the erythrocytic cycle. Aberrant structural modification was observed by electron microscopy, showing the separation of the two nuclear membrane leaflets as well as other subcellular membranes, such as from the digestive vacuole. Importantly, in vivo studies using ECM revealed a reduction in blood parasitemia and cerebral edema when mice were treated for 6 consecutive days upon infection.

CONCLUSIONS

These data suggest a potential effect of eugenol against Plasmodium sp. with an impact on cerebral malaria.

GENERAL SIGNIFICANCE

Our results provide a rational basis for the use of eugenol in therapeutic strategies to the treatment of malaria.

Antiplasmodial activity of sulfonylhydrazones: in vitro and in silico approaches

Malaria is still a life-threatening public health issue, and the upsurge of resistant strains requires continuous generation of active molecules. In this work, 35 sulfonylhydrazone derivatives were synthesized and evaluated against Plasmodium falciparum chloroquine-sensitive (3D7) and resistant (W2) strains. The most promising compound, 5b, had an IC₅₀ of 0.22 μM against W2 and was less cytotoxic and 26-fold more selective than chloroquine. The structure-activity relationship model, statistical analysis and molecular modeling studies suggested that antiplasmodial activity was related to hydrogen bond acceptor count, molecular weight and partition coefficient of octanol/water and displacement of frontier orbitals to the heteroaromatic ring beside the imine bond. This study demonstrates that the synthesized molecules with a simple scaffold allow the hit-to-lead process for new antimalarials to commence.

Structure of the Plasmodium falciparum PfSERA5 pseudo-zymogen

PfSERA5, a significantly abundant protein present within the parasitophorous vacuole (PV) and essential for normal growth during the blood-stage life cycle of the malaria parasite Plasmodium falciparum, displays structural similarity to many other cysteine proteases. However, PfSERA5 does not exhibit any detectable protease activity and therefore the role of the PfSERA5 papain-like domain (PfSERA5E), thought to remain bound to its cognate prodomain, remains unknown. In this study, we present a revised structure of the central PfSERA5E domain at a resolution of 1.2 Å, and the first structure of the "zymogen" of this papain-like domain including its cognate prodomain (PfSERA5PE) to 2.2 Å resolution. PfSERA5PE is somewhat structurally similar to that of other known proenzymes, retaining the conserved overall folding and orientation of the prodomain through, and occluding, the archetypal papain-like catalytic triad "active-site" cleft, in the same reverse direction as conventional prodomains. Our findings are congruent with previously identified structures of PfSERA5E and of similar "zymogens" and provide a foundation for further investigation into the function of PfSERA5.

Plasmodium falciparum parasites exit the infected erythrocyte after haemolysis with saponin and streptolysin O

Malaria is caused by unicellular parasites of the genus Plasmodium, which reside in erythrocytes during the clinically relevant stage of infection. To separate parasite from host cell material, haemolytic agents such as saponin are widely used. Previous electron microscopy studies on saponin-treated parasites reported both, parasites enclosed by the erythrocyte membrane and liberated from the host cell. These ambiguous reports prompted us to investigate haemolysis by live-cell time-lapse microscopy. Using either saponin or streptolysin O to lyse Plasmodium falciparum-infected erythrocytes, we found that ring-stage parasites efficiently exit the erythrocyte upon haemolysis. For late-stage parasites, we found that only approximately half were freed, supporting the previous electron microscopy studies. Immunofluorescence imaging indicated that freed parasites were surrounded by the parasitophorous vacuolar membrane. These results may be of interest for future work using haemolytic agents to enrich for parasite material.

Plug for the parasitophorous duct: a solution of two conundra

BACKGROUND

We present two conundra in the biology of intraerythrocytic malaria parasite: how an apparent open parasitophorous duct provide direct access of only a select set of serum proteins to the parasitophorous vacuole, and how proteases mediate membrane lysis to allow merozoite egress.

SOLUTION

We posit the existence of a parasitophorous vacuolar duct plug that is originally formed from a tight junction (or parts thereof) between merozoite apical surface and red blood cell plasma membrane, which by moving over the parasite surface towards the posterior end draws the parasite into the host cell interior, and by remaining at the passage orifice provides a location of transporter(s) for import of serum proteins into parasitophorous vacuole and an opening for merozoite egress upon its dissolution/dismantling through protease(s) action.

CONCLUSION

This notion obviates the need of a distinct intact parasitophorous vacuolar membrane, which in the proposed model is an extension of the red blood cell membrane but still forms an intracellular compartment for parasite growth and development. The model is testable using existing high-resolution electron and X-ray tomography tools.

Polyphyletic origin, intracellular invasion, and meiotic genes in the putatively asexual agamococcidians (Apicomplexa incertae sedis)

Agamococcidians are enigmatic and poorly studied parasites of marine invertebrates with unexplored diversity and unclear relationships to other sporozoans such as the human pathogens Plasmodium and Toxoplasma. It is believed that agamococcidians are not capable of sexual reproduction, which is essential for life cycle completion in all well studied parasitic apicomplexans. Here, we describe three new species of agamococcidians belonging to the genus Rhytidocystis. We examined their cell morphology and ultrastructure, resolved their phylogenetic position by using near-complete rRNA operon sequences, and searched for genes associated with meiosis and oocyst wall formation in two rhytidocystid transcriptomes. Phylogenetic analyses consistently recovered rhytidocystids as basal coccidiomorphs and away from the corallicolids, demonstrating that the order Agamococcidiorida Levine, 1979 is polyphyletic. Light and transmission electron microscopy revealed that the development of rhytidocystids begins inside the gut epithelial cells, a characteristic which links them specifically with other coccidiomorphs to the exclusion of gregarines and suggests that intracellular invasion evolved early in the coccidiomorphs. We propose a new superorder Eococcidia for early coccidiomorphs. Transcriptomic analysis demonstrated that both the meiotic machinery and oocyst wall proteins are preserved in rhytidocystids. The conservation of meiotic genes and ultrastructural similarity of rhytidocystid trophozoites to macrogamonts of true coccidians point to an undescribed, cryptic sexual process in the group.

A Plasmodium cysteine protease required for efficient transition from the liver infection stage

The transitions between developmental stages are critical points in the Plasmodium life cycle. The development of Plasmodium in the livers of their mammalian hosts bridges malaria transmission and the onset of clinical symptoms elicited by red blood cell infection. The egress of Plasmodium parasites from the liver must be a carefully orchestrated process to ensure a successful switch to the blood stage of infection. Cysteine protease activity is known to be required for liver-stage Plasmodium egress, but the crucial cysteine protease(s) remained unidentified. Here, we characterize a member of the papain-like cysteine protease family, Plasmodium berghei serine repeat antigen 4 (PbSERA4), that is required for efficient initiation of blood-stage infection. Through the generation PbSERA4-specific antisera and the creation of transgenic parasites expressing fluorescently tagged protein, we show that PbSERA4 is expressed and proteolytically processed in the liver and blood stages of infection. Targeted disruption of PbSERA4 results in viable and virulent blood-stage parasites. However, upon transmission from mosquitoes to mice, Pbsera4(-) parasites displayed a reduced capacity to initiate a new round of asexual blood-stage replication. Our results from cultured cells indicate that this defect results from an inability of the PbSERA4-deficient parasites to egress efficiently from infected cells at the culmination of liver-stage development. Protection against infection with wildtype P. berghei could be generated in animals in which Pbsera4(-) parasites failed to establish infection. Our findings confirm that liver-stage merozoite release is an active process and demonstrate that this parasite-encoded cysteine protease contributes to parasite escape from the liver.

Plasmodium parasites cause over 200 million cases of malaria every year. When parasites are transmitted by mosquito bite, they initially colonize the liver before they move into the blood and cause disease. During successful transition from the liver into the blood, Plasmodium cloak themselves in host plasma membrane as they egress from the liver cells. Although some aspects of how Plasmodium exit their host hepatocytes appear unique, certain attributes are shared across diverse pathogens. For example, protease activity is required not only for multiple stages of Plasmodium exit, but is also involved in the egress of some bacteria and other protozoan. Here we characterize a protease in Plasmodium berghei that is expressed in the liver and conserved across Plasmodium species. Through gene targeting, we found PbSERA4 is required for efficient egress of Plasmodium from the liver. In the absence of this protease the transition between the liver and blood stages of growth is prolonged due to inefficient parasite release from liver cells. These findings provide new insights into the function of a conserved Plasmodium protease and into the process of Plasmodium escape from the liver.

Crossing the Vacuolar Rubicon: Structural Insights into Effector Protein Trafficking in Apicomplexan Parasites

Apicomplexans form a large phylum of parasitic protozoa, including the genera Plasmodium, Toxoplasma, and Cryptosporidium, the causative agents of malaria, toxoplasmosis, and cryptosporidiosis, respectively. They cause diseases not only in humans but also in animals, with dramatic consequences in agriculture. Most apicomplexans are vacuole-dwelling and obligate intracellular parasites; as they invade the host cell, they become encased in a parasitophorous vacuole (PV) derived from the host cellular membrane. This creates a parasite-host interface that acts as a protective barrier but also constitutes an obstacle through which the pathogen must import nutrients, eliminate wastes, and eventually break free upon egress. Completion of the parasitic life cycle requires intense remodeling of the infected host cell. Host cell subversion is mediated by a subset of essential effector parasitic proteins and virulence factors actively trafficked across the PV membrane. In the malaria parasite Plasmodium, a unique and highly specialized ATP-driven vacuolar secretion system, the Plasmodium translocon of exported proteins (PTEX), transports effector proteins across the vacuolar membrane. Its core is composed of the three essential proteins EXP2, PTEX150, and HSP101, and is supplemented by the two auxiliary proteins TRX2 and PTEX88. Many but not all secreted malarial effector proteins contain a vacuolar trafficking signal or Plasmodium export element (PEXEL) that requires processing by an endoplasmic reticulum protease, plasmepsin V, for proper export. Because vacuolar parasitic protein export is essential to parasite survival and virulence, this pathway is a promising target for the development of novel antimalarial therapeutics. This review summarizes the current state of structural and mechanistic knowledge on the Plasmodium parasitic vacuolar secretion and effector trafficking pathway, describing its most salient features and discussing the existing differences and commonalities with the vacuolar effector translocation MYR machinery recently described in Toxoplasma and other apicomplexans of significance to medical and veterinary sciences.

Differential Fractionation of Erythrocytes Infected by Plasmodium berghei

The study of host/pathogen interactions at the cellular level during Plasmodium intra-erythrocytic cycle requires differential extraction techniques aiming to analyze the different compartments of the infected cell. Various protocols have been proposed in the literature to study specific compartments and/or membranes in the infected erythrocyte. The task remains delicate despite the use of enzymes or detergents theoretically capable of degrading specific membranes inside the infected cell. The remit of this protocol is to propose a method to isolate the erythrocyte cytosol and ghosts from the other compartments of the infected cell via a percoll gradient. Also, the lysis of the erythrocyte membrane is done using equinatoxin II, which has proven to be more effective at erythrocyte lysis regardless of the cell infection status, compared to the commonly used streptolysin. The parasitophorous vacuole (PV) content is collected after saponin lysis, before recovering membrane and parasite cytosol proteins by Triton X-100 lysis. The lysates thus obtained are analyzed by Western blot to assess the accuracy of the various extraction steps. This protocol allows the separation of the host compartment from the parasite compartments (PV and parasite), leading to potential studies of host proteins as well as parasite proteins exported to the host cell.