Fractionation and identification of proteins by 2-DE and MS: towards a proteomic analysis ofPlasmodium falciparum

A proteomic glimpse into the effect of antimalarial drugs on Plasmodium falciparum proteome towards highlighting possible therapeutic targets

There is no effective vaccine against malaria; therefore, chemotherapy is to date the only choice to fight against this infectious disease. However, there is growing evidences of drug-resistance mechanisms in malaria treatments. Therefore, the identification of new drug targets is an urgent need for the clinical management of the disease. Proteomic approaches offer the chance of determining the effects of antimalarial drugs on the proteome of Plasmodium parasites. Accordingly, we reviewed the effects of antimalarial drugs on the Plasmodium falciparum proteome pointing out the relevance of several proteins as possible drug targets in malaria treatment. In addition, some of the P. falciparum stage-specific altered proteins and parasite-host interactions might play important roles in pathogenicity, survival, invasion and metabolic pathways and thus serve as potential sources of drug targets. In this review, we have identified several proteins, including thioredoxin reductase, helicases, peptidyl-prolyl cis-trans isomerase, endoplasmic reticulum-resident calcium-binding protein, choline/ethanolamine phosphotransferase, purine nucleoside phosphorylase, apical membrane antigen 1, glutamate dehydrogenase, hypoxanthine guanine phosphoribosyl transferase, heat shock protein 70x, knob-associated histidine-rich protein and erythrocyte membrane protein 1, as promising antimalarial drugs targets. Overall, proteomic approaches are able to partially facilitate finding possible drug targets. However, the integration of other 'omics' and specific pharmaceutical techniques with proteomics may increase the therapeutic properties of the critical proteins identified in the P. falciparum proteome.

The Identification of Native Epitopes Eliciting a Protective High-Affinity Immunoglobulin Subclass Response to Blood Stages of Plasmodium falciparum: Protocol for Observational Studies

Background

Antibodies to blood stages protective against complications of Plasmodium falciparum infection were found to be of immunoglobulin G 1 (IgG1) and IgG3 subclasses and of high affinity to the target epitopes. These target epitopes cannot be characterized using recombinant antigens because of a lack of appropriate glycosylation, phosphorylation, methylation, and bisulfide bond formation, which determine the structure of conformational and nonlinear epitopes within the tertiary and quaternary structures of native P. falciparum antigens.

Objective

This study aims to develop a method for the comprehensive detection of all P. falciparum schizont antigens, eliciting a protective immune response.

Methods

Purified parasitophorous vacuole membrane–enclosed merozoite structures (PEMSs) containing native schizont antigens are initially generated, separated by two-dimensional (2D) gel electrophoresis and blotted onto nitrocellulose. Antigens eliciting a protective antibody response are visualized by incubation with sera from patients with clinical immunity. This is followed by the elution of low-affinity antibodies with urea and detection of protective antibody responses by incubation with anti-IgG1 and anti-IgG3 antibodies, which were conjugated to horseradish peroxidase. This is followed by visualization with a color reaction. Blot signals are normalized by relating to the intensity of blot staining with a reference antibody and housekeeping antigens. Results are corrected for intensity of exposure by the relation of antibody responses to global P. falciparum antibody titers. Antigens eliciting the protective responses are identified as immunorelevant from the comparison of spot positions, indicating high-affinity IgG1 or IgG3 responses on the western blot, which is unique to or consistently more intensive in clinically immune individuals compared with nonimmune individuals. The results obtained are validated by using affinity chromatography.

Results

Another group previously applied 2D western blotting to analyze antibody responses to P. falciparum. The sera of patients allowed the detection of 42 antigenic spots on the 2D immunoblot. The spots detected were excised and subjected to mass spectrometry for identification. A total of 19 protein spots were successfully identified and corresponded to 13 distinct proteins. Another group used immunoaffinity chromatography to identify antigens bound by IgGs produced by mice with enhanced immunity to Plasmodium yoelii. Immunorelevant antigens were isolated and identified by immobilizing immunoglobulin from immune mice to a Sephadex column and then passing a blood-stage antigen mixture through the column followed by the elution of specific bound antigens with sodium deoxycholate and the identification of those antigens by western blotting with specific antibodies.

Conclusions

2D western blotting using native antigens has the potential to identify antibody responses selective for specific defined isomeric forms of the same protein, including isoforms (protein species) generated by posttranscriptional modifications such as phosphorylation, glycosylation, and methylation. The process involved in 2D western blotting enables highly sensitive detection, high resolution, and preservation of antibody responses during blotting. Validation by immunoaffinity chromatography can compensate for the antigen loss associated with the blotting process. It has the potential for indirect quantification of protective antibody responses by enabling quantification of the amount of eluted antibody bound antigens through mass spectrometry.

International Registered Report Identifier (IRRID)

PRR1-10.2196/15690

The use of proteomics for the identification of promising vaccine and diagnostic biomarkers in Plasmodium falciparum

Plasmodium falciparum is the main cause of severe malaria in humans that can lead to death. There is growing evidence of drug-resistance in P. falciparum treatment, and the design of effective vaccines remains an ongoing strategy to control the disease. On the other hand, the recognition of specific diagnostic markers for P. falciparum can accelerate the diagnosis of this parasite in the early stages of infection. Therefore, the identification of novel antigenic proteins especially by proteomic tools is urgent for vaccination and diagnosis of P. falciparum. The proteome diversity of the life cycle stages of P. falciparum, the altered proteome of P. falciparum-infected human sera and altered proteins in P. falciparum-infected erythrocytes could be proposed as appropriate proteins for the aforementioned aims. Accordingly, this review highlights and proposes different proteins identified using proteomic approaches as promising markers in the diagnosis and vaccination of P. falciparum. It seems that most of the candidates identified in this study were able to elicit immune responses in the P. falciparum-infected hosts and they also played major roles in the life cycle, pathogenicity and key pathways of this parasite.

Vaccine candidate discovery for the next generation of malaria vaccines

Although epidemiological observations, IgG passive transfer studies and experimental infections in humans all support the feasibility of developing highly effective malaria vaccines, the precise antigens that induce protective immunity remain uncertain. Here, we review the methodologies applied to vaccine candidate discovery for Plasmodium falciparum malaria from the pre- to post-genomic era. Probing of genomic and cDNA libraries with antibodies of defined specificities or functional activity predominated the former, whereas reverse vaccinology encompassing high throughput in silico analyses of genomic, transcriptomic or proteomic parasite data sets is the mainstay of the latter. Antibody-guided vaccine design spanned both eras but currently benefits from technological advances facilitating high-throughput screening and downstream applications. We make the case that although we have exponentially increased our ability to identify numerous potential vaccine candidates in a relatively short space of time, a significant bottleneck remains in their validation and prioritization for evaluation in clinical trials. Longitudinal cohort studies provide supportive evidence but results are often conflicting between studies. Demonstration of antigen-specific antibody function is valuable but the relative importance of one mechanism over another with regards to protection remains undetermined. Animal models offer useful insights but may not accurately reflect human disease. Challenge studies in humans are preferable but prohibitively expensive. In the absence of reliable correlates of protection, suitable animal models or a better understanding of the mechanisms underlying protective immunity in humans, vaccine candidate discovery per se may not be sufficient to provide the paradigm shift necessary to develop the next generation of highly effective subunit malaria vaccines.

Plasmodium Helical Interspersed Subtelomeric (PHIST) Proteins, at the Center of Host Cell Remodeling

During the asexual cycle, Plasmodium falciparum extensively remodels the human erythrocyte to make it a suitable host cell. A large number of exported proteins facilitate this remodeling process, which causes erythrocytes to become more rigid, cytoadherent, and permeable for nutrients and metabolic products. Among the exported proteins, a family of 89 proteins, called the Plasmodium helical interspersed subtelomeric (PHIST) protein family, has been identified. While also found in other Plasmodium species, the PHIST family is greatly expanded in P. falciparum. Although a decade has passed since their first description, to date, most PHIST proteins remain uncharacterized and are of unknown function and localization within the host cell, and there are few data on their interactions with other host or parasite proteins. However, over the past few years, PHIST proteins have been mentioned in the literature at an increasing rate owing to their presence at various localizations within the infected erythrocyte. Expression of PHIST proteins has been implicated in molecular and cellular processes such as the surface display of PfEMP1, gametocytogenesis, changes in cell rigidity, and also cerebral and pregnancy-associated malaria. Thus, we conclude that PHIST proteins are central to host cell remodeling, but despite their obvious importance in pathology, PHIST proteins seem to be understudied. Here we review current knowledge, shed light on the definition of PHIST proteins, and discuss these proteins with respect to their localization and probable function. We take into consideration interaction studies, microarray analyses, or data from blood samples from naturally infected patients to combine all available information on this protein family.

Plasmodium falciparum malaria: proteomic studies

Despite advances in treatment and campaigns for prevention and control of malaria on the various continents where it is still rampant, this disease remains significantly relevant to the contemporary world. Plasmodium falciparum is the organism that is mainly responsible for severe malaria, which is characterized by disturbances in different organs and systems, with possibly fatal outcomes. Although incipient, proteomic studies of malaria have yielded favorable prospects for elucidating the biological aspects of Plasmodium as well as the pathophysiological, diagnostic, prophylactic, and therapeutic mechanisms of the disease. Thus, the aim of the present article is to present a brief review of the applications of proteomic analysis in P. falciparum malaria.

Mature Erythrocyte Surface Antigen Protein Identified in the Serum of Plasmodium falciparum-Infected Patients

This study was performed to identify circulating Plasmodium falciparum proteins in patient serum, which may be useful as diagnostic markers. Depletion of highly abundant proteins from each pooled serum sample obtained from P. falciparum-infected patients and healthy individuals was performed using the Proteoseek Antibody-Based Albumin/IgG Removal Kit (Thermo Scientific, Rockford, IL). In analysis 1, the depleted serum was analyzed directly by NanoLC-MS/MS. In analysis 2, the depleted serum was separated by two-dimensional electrophoresis followed by western blot analysis. Subsequently, the selected band was analyzed by NanoLC-MS/MS. The result of analysis 1 revealed the presence of two mature erythrocyte surface antigen (MESA) proteins and chloroquine resistance transporter protein (PfCRT). In addition, analysis 2 revealed an antigenic 75-kDa band when the membrane was probed with purified IgG from the pooled serum obtained from P. falciparum-infected patients. MS/MS analysis of this protein band revealed fragments of P. falciparum MESA proteins. Thus, in this study, two different analyses revealed the presence of Plasmodium MESA protein in pooled serum from malaria patients; thus, this protein should be further investigated to determine its usefulness as a diagnostic marker.

Malaria proteomics: insights into the parasite-host interactions in the pathogenic space

Proteomics is improving malaria research by providing global information on relevant protein sets from the parasite and the host in connection with its cellular structures and specific functions. In the last decade, reports have described biologically significant elements in the proteome of Plasmodium, which are selectively targeted and quantified, allowing for sensitive and high-throughput comparisons. The identification of molecules by which the parasite and the host react during the malaria infection is crucial to the understanding of the underlying pathogenic mechanisms. Hence, proteomics is playing a major role by defining the elements within the pathogenic space between both organisms that change across the parasite life cycle in association with the host transformation and response. Proteomics has identified post-translational modifications in the parasite and the host that are discussed in terms of functional interactions in malaria parasitism. Furthermore, the contribution of proteomics to the investigation of immunogens for potential vaccine candidates is summarized. The malaria-specific technological advances in proteomics are particularly suited now for identifying host-parasite interactions that could lead to promising targets for therapy, diagnosis or prevention. In this review, we examine the knowledge gained on the biology, pathogenesis, immunity and diagnosis of Plasmodium infection from recent proteomic studies. This article is part of a Special Issue entitled: Trends in Microbial Proteomics.

Module-based subnetwork alignments reveal novel transcriptional regulators in malaria parasite Plasmodium falciparum

Background

Malaria causes over one million deaths annually, posing an enormous health and economic burden in endemic regions. The completion of genome sequencing of the causative agents, a group of parasites in the genus Plasmodium, revealed potential drug and vaccine candidates. However, genomics-driven target discovery has been significantly hampered by our limited knowledge of the cellular networks associated with parasite development and pathogenesis. In this paper, we propose an approach based on aligning neighborhood PPI subnetworks across species to identify network components in the malaria parasite P. falciparum.

Results

Instead of only relying on sequence similarities to detect functional orthologs, our approach measures the conservation between the neighborhood subnetworks in protein-protein interaction (PPI) networks in two species, P. falciparum and E. coli. 1,082 P. falciparum proteins were predicted as functional orthologs of known transcriptional regulators in the E. coli network, including general transcriptional regulators, parasite-specific transcriptional regulators in the ApiAP2 protein family, and other potential regulatory proteins. They are implicated in a variety of cellular processes involving chromatin remodeling, genome integrity, secretion, invasion, protein processing, and metabolism.

Conclusions

In this proof-of-concept study, we demonstrate that a subnetwork alignment approach can reveal previously uncharacterized members of the subnetworks, which opens new opportunities to identify potential therapeutic targets and provide new insights into parasite biology, pathogenesis and virulence. This approach can be extended to other systems, especially those with poor genome annotation and a paucity of knowledge about cellular networks.

Comparative Genomics and Systems Biology of Malaria Parasites Plasmodium

Malaria is a serious infectious disease that causes over one million deaths yearly. It is caused by a group of protozoan parasites in the genus Plasmodium. No effective vaccine is currently available and the elevated levels of resistance to drugs in use underscore the pressing need for novel antimalarial targets. In this review, we survey omics centered developments in Plasmodium biology, which have set the stage for a quantum leap in our understanding of the fundamental processes of the parasite life cycle and mechanisms of drug resistance and immune evasion.

Isolation of erythrocytes infected with viable early stages of Plasmodium falciparum by flow cytometry

The erythrocytic life cycle of Plasmodium falciparum is highly associated with severe clinical symptoms of malaria that causes hundreds of thousands of death each year. The parasite develops within human erythrocytes leading to the disruption of the infected red blood cell (iRBC) prior to the start of a new cycle of erythrocyte infection. Emerging mechanisms of resistance against antimalarial drugs require improved knowledge about parasite's blood stages to facilitate new alternative antimalarial strategies. For the analysis of young blood stages of Plasmodium at the molecular level, the isolation of ring stages is essential. However, early stages can hardly be separated from both, late stages and non-infected red blood cells using conventional methods. Here, iRBCs were stained with the DNA-binding dyes Vybrant® DyeCycle™ Violet and SYBR® Green I. Subsequently, cells were subjected to flow-cytometric analysis. This enabled the discrimination of early stage iRBCs as well as late-stage iRBCs from non-infected erythrocytes and the properties of the used dyes were evaluated. Moreover, early stage iRBCs were isolated with high purity (>98%) by FACS. Subsequently, development of sorted early stages of the parasite was monitored over time and compared with control cultures. The described flow cytometry method, based on staining with Vybrant DyeCycle Violet, allows the isolation of viable ring stages of the malarial agent P. falciparum, and thereby provides the basis for new, broad-range molecular investigations of the parasite.

Plasmodium falciparum infection-induced changes in erythrocyte membrane proteins

Over the past decade, advances in proteomic and mass spectrometry techniques and the sequencing of the Plasmodium falciparum genome have led to an increasing number of studies regarding the parasite proteome. However, these studies have focused principally on parasite protein expression, neglecting parasite-induced variations in the host proteome. Here, we investigated P. falciparum-induced modifications of the infected red blood cell (iRBC) membrane proteome, taking into account both host and parasite proteome alterations. Furthermore, we also determined if some protein changes were associated with genotypically distinct P. falciparum strains. Comparison of host membrane proteomes between iRBCs and uninfected red blood cells using fluorescence-based proteomic approaches, such as 2D difference gel electrophoresis revealed that more than 100 protein spots were highly up-represented (fold change increase greater than five) following P. falciparum infection for both strains (i.e. RP8 and Institut Pasteur Pregnancy Associated Malaria). The majority of spots identified by mass spectrometry corresponded to Homo sapiens proteins. However, infection-induced changes in host proteins did not appear to affect molecules located at the outer surface of the plasma membrane. The under-representation of parasite proteins could not be attributed to deficient parasite protein expression. Thus, this study describes for the first time that considerable host protein modifications were detected following P. falciparum infection at the erythrocyte membrane level. Further analysis of infection-induced host protein modifications will improve our knowledge of malaria pathogenesis.

Quantitative time-course profiling of parasite and host cell proteins in the human malaria parasite Plasmodium falciparum

Studies of the Plasmodium falciparum transcriptome have shown that the tightly controlled progression of the parasite through the intra-erythrocytic developmental cycle (IDC) is accompanied by a continuous gene expression cascade in which most expressed genes exhibit a single transcriptional peak. Because the biochemical and cellular functions of most genes are mediated by the encoded proteins, understanding the relationship between mRNA and protein levels is crucial for inferring biological activity from transcriptional gene expression data. Although studies on other organisms show that <50% of protein abundance variation may be attributable to corresponding mRNA levels, the situation in Plasmodium is further complicated by the dynamic nature of the cyclic gene expression cascade. In this study, we simultaneously determined mRNA and protein abundance profiles for P. falciparum parasites during the IDC at 2-hour resolution based on oligonucleotide microarrays and two-dimensional differential gel electrophoresis protein gels. We find that most proteins are represented by more than one isoform, presumably because of post-translational modifications. Like transcripts, most proteins exhibit cyclic abundance profiles with one peak during the IDC, whereas the presence of functionally related proteins is highly correlated. In contrast, the abundance of most parasite proteins peaks significantly later (median 11 h) than the corresponding transcripts and often decreases slowly in the second half of the IDC. Computational modeling indicates that the considerable and varied incongruence between transcript and protein abundance may largely be caused by the dynamics of translation and protein degradation. Furthermore, we present cyclic abundance profiles also for parasite-associated human proteins and confirm the presence of five human proteins with a potential role in antioxidant defense within the parasites. Together, our data provide fundamental insights into transcript-protein relationships in P. falciparum that are important for the correct interpretation of transcriptional data and that may facilitate the improvement and development of malaria diagnostics and drug therapy.

Fasciola hepatica and Schistosoma mansoni: identification of common proteins by comparative proteomic analysis

It is not unusual to find common molecules among parasites of different species, genera, or phyla. When those molecules are antigenic, they may be used for developing drugs or vaccines that simultaneously target different species or genera of parasite. In the present study, we used a proteomic-based approach to identify proteins that are common to adult Fasciola hepatica and Schistosoma mansoni. Whole-worm extracts from each parasite were separated by 2-dimensional electrophoresis (2-DE), and digital images of both proteomes were superimposed using imaging software to identify proteins with identical isoelectric points and molecular weights. Protein identities were determined by mass spectrometry. Imaging and immunoblot analyses identified 28 immunoreactive proteins that are common to both parasites. Among these molecules are antioxidant proteins (thioredoxin and glutathione-S-transferase), glycolytic enzymes (glyceraldehyde 6-phosphate dehydrogenase and enolase), proteolytic enzymes (cathepsin-L and -D), inhibitors (Kunitz-type, Stefin-1), proteins with chaperone activity (heat shock protein 70 and fatty acid-binding protein), and structural proteins (calcium-binding protein, actin, and myosin). Some of the identified proteins could be used to develop drugs and vaccines against fascioliasis and schistosomiasis.

2-D DIGE analysis of the proteome of extracts from peanut variants reveals striking differences in major allergen contents

Over the last decade, an increasing prevalence of peanut allergies was observed worldwide. Peanuts are meanwhile categorized among the most dangerous food allergens. This is particularly relevant since peanut-derived ingredients are widely used in industrial food production. To minimize the problem of hidden food allergens causing severe anaphylactic reactions, pre-packaged food containing peanut components needs to be classified according to European ruling since 2005. Food companies search for strategies to reduce the allergenicity of peanut-derived food additives either by genetically altering the allergen content or by identifying peanut varieties with low levels of major allergens. In our study, we focused on peanut extracts from Indonesia that apparently contain lower levels of the major Arachis hypogaea allergen 1 (Ara h 1). Basic extracts of Virginia-type and Indonesian peanuts were compared by 1- and 2-DE. We identified more than hundred individual components in these extracts by MS and provide a high-resolution allergen map that also includes so far unknown fragments of major peanut allergens. The reduced level of Ara h 1 associated with a significantly lower abundance of the most potent peanut allergen Ara h 2 in various Indonesian peanuts was also confirmed by Western blotting with monoclonal antibodies and sera of allergic patients.

The malarial parasite Plasmodium falciparum imports the human protein peroxiredoxin 2 for peroxide detoxification

Coevolution of the malarial parasite and its human host has resulted in a complex network of interactions contributing to the homeodynamics of the host-parasite unit. As a rapidly growing and multiplying organism, Plasmodium falciparum depends on an adequate antioxidant defense system that is efficient despite the absence of genuine catalase and glutathione peroxidase. Using different experimental approaches, we demonstrate that P. falciparum imports the human redox-active protein peroxiredoxin 2 (hPrx-2, hTPx1) into its cytosol. As shown by confocal microscopy and immunogold electron microscopy, hPrx-2 is also present in the Maurer's clefts, organelles that are described as being involved in parasite protein export. Enzyme kinetic analyses prove that hPrx-2 accepts Plasmodium cytosolic thioredoxin 1 as a reducing substrate. hPrx-2 accounts for roughly 50% of thioredoxin peroxidase activity in parasite extracts, thus indicating a functional role of hPrx-2 as an enzymatic scavenger of peroxides in the parasite. Under chloroquine treatment, a drug promoting oxidative stress, the abundance of hPrx-2 in the parasite increases significantly. P. falciparum has adapted to adopt the hPrx-2, thereby using the host protein for its own purposes.

Enrichment and analysis of secretory lysosomes from lymphocyte populations

BACKGROUND

In specialized cells, such as mast cells, macrophages, T lymphocytes and Natural Killer cells in the immune system and for instance melanocytes in the skin, secretory lysosomes (SL) have evolved as bifunctional organelles that combine degradative and secretory properties. Mutations in lysosomal storage, transport or sorting molecules are associated with severe immunodeficiencies, autoimmunity and (partial) albinism. In order to analyze the function and content of secretory lysosomes in different cell populations, an efficient enrichment of these organelles is mandatory.

RESULTS

Based on a combination of differential and density gradient centrifugation steps, we provide a protocol to enrich intact SL from expanded hematopoietic cells, here T lymphocytes and Natural Killer cells. Individual fractions were initially characterized by Western blotting using antibodies against an array of marker proteins for intracellular compartments. As indicated by the presence of LAMP-3 (CD63) and FasL (CD178), we obtained a selective enrichment of SL in one of the resulting organelle fractions. The robustness and reproducibility of the applied separation protocol was examined by a high-resolution proteome analysis of individual SL preparations of different donors by 2D difference gel electrophoresis (2D-DIGE).

CONCLUSION

The provided protocol is readily applicable to enrich and isolate intact secretory vesicles from individual cell populations. It can be used to compare SL of normal and transformed cell lines or primary cell populations from healthy donors and patients with lysosomal storage or transport diseases, or from corresponding mutant mice. A subsequent proteome analysis allows the characterization of molecules involved in lysosomal maturation and cytotoxic effector function at high-resolution.

Quantitative protein expression profiling reveals extensive post-transcriptional regulation and post-translational modifications in schizont-stage malaria parasites

BACKGROUND

Malaria is a one of the most important infectious diseases and is caused by parasitic protozoa of the genus Plasmodium. Previously, quantitative characterization of the P. falciparum transcriptome demonstrated that the strictly controlled progression of these parasites through their intra-erythrocytic developmental cycle is accompanied by a continuous cascade of gene expression. Although such analyses have proven immensely useful, the correlations between abundance of transcripts and their cognate proteins remain poorly characterized.

RESULTS

Here, we present a quantitative time-course analysis of relative protein abundance for schizont-stage parasites (34 to 46 hours after invasion) based on two-dimensional differential gel electrophoresis of protein samples labeled with fluorescent dyes. For this purpose we analyzed parasite samples taken at 4-hour intervals from a tightly synchronized culture and established more than 500 individual protein abundance profiles with high temporal resolution and quantitative reproducibility. Approximately half of all profiles exhibit a significant change in abundance and 12% display an expression peak during the observed 12-hour time interval. Intriguingly, identification of 54 protein spots by mass spectrometry revealed that 58% of the corresponding proteins--including actin-I, enolase, eukaryotic initiation factor (eIF)4A, eIF5A, and several heat shock proteins--are represented by more than one isoform, presumably caused by post-translational modifications, with the various isoforms of a given protein frequently showing different expression patterns. Furthermore, comparisons with transcriptome data generated from the same parasite samples reveal evidence of significant post-transcriptional gene expression regulation.

CONCLUSIONS

Together, our data indicate that both post-transcriptional and post-translational events are widespread and of presumably great biological significance during the intra-erythrocytic development of P. falciparum.

Food vacuole proteome of the malarial parasite Plasmodium falciparum

The Plasmodium falciparum food vacuole (FV) is a lysosome-like organelle where erythrocyte hemoglobin digestion occurs. It is a favorite target in the development of antimalarials. We have used a tandem mass spectrometry approach to investigate the proteome of an FV-enriched fraction and identified 116 proteins. The electron microscopy analysis and the Western blot data showed that the major component of the fraction was the FV and, as expected, the majority of previously known FV markers were recovered. Of particular interest, several proteins involved in vesicle-mediated trafficking were identified, which are likely to play a key role in FV biogenesis and/or FV protein trafficking. Recovery of parasite surface proteins lends support to the cytostomal pathway of hemoglobin ingestion as a FV trafficking route. We have identified 32 proteins described as hypothetical in the databases. This insight into FV protein content provides new clues towards understanding the biological function of this organelle in P. falciparum.

Microscale solution isoelectric focusing as an effective strategy enabling containment of hemeoglobin-derived products for high-resolution gel-based analysis of the Plasmodium falciparum proteome

The high hemeozoin (beta-hemeatin) content of Plasmodium falciparum lysates imposes severe limitations on the analysis of the malarial proteome, in particular compromising the loading capacities of two-dimensional gels. Here we report on the adaptation of a recently developed solution-phase isoelectric focusing-based fractionation technique as a prefractionation strategy for efficient containment of hemeoglobin-derived products and complexity reduction, to facilitate the high-resolution gel-based quantitative analysis of plasmodial lysates.

Proteome analysis of new antimalarial endoperoxide against Plasmodium falciparum

N-89, a new antimalarial endoperoxide, was selected as a promising antimalarial compound showing high activity and selectivity. To study the mechanism of N-89 action, N-89 resistant strain (NRC10) was obtained by intermittent drug pressure. NRC10 had a tenfold increase in the EC(50) value of N-89. No cross-resistance was obtained with other antimalarial compounds. Comparative proteome analysis of N-89 sensitive and NRC10 strains revealed over-expression of 12 spots and down-regulation of 14 spots in NRC10. Fifteen proteins were identified of Plasmodium falciparum origin. The identified proteins representing several functions, mainly related to the glycolytic pathway, and metabolism of protein and lipid. Our results suggest that identified proteins may be candidates of antimalarial endoperoxide targets.