A mitogen-activated protein kinase regulates male gametogenesis and transmission of the malaria parasite Plasmodium berghei

Differentiation of malaria parasites into sexual forms (gametocytes) in the vertebrate host and their subsequent development into gametes in the mosquito vector are crucial steps in the completion of the parasite's life cycle and transmission of the disease. The molecular mechanisms that regulate the sexual cycle are poorly understood. Although several signal transduction pathways have been implicated, a clear understanding of the pathways involved has yet to emerge. Here, we show that a Plasmodium berghei homologue of Plasmodium falciparum mitogen-activated kinase-2 (Pfmap-2), a gametocyte-specific mitogen-activated protein kinase (MAPK), is required for male gamete formation. Parasites lacking Pbmap-2 are competent for gametocytogenesis, but exflagellation of male gametocytes, the process that leads to male gamete formation, is almost entirely abolished in mutant parasites. Consistent with this result, transmission of mutant parasites to mosquitoes is grossly impaired. This finding identifies a crucial role for a MAPK pathway in malaria transmission.     

Mitosis in the human malaria parasite Plasmodium falciparum

Malaria is caused by intraerythrocytic protozoan parasites belonging to Plasmodium spp. (phylum Apicomplexa) that produce significant morbidity and mortality, mostly in developing countries. Plasmodium parasites have a complex life cycle that includes multiple stages in anopheline mosquito vectors and vertebrate hosts. During the life cycle, the parasites undergo several cycles of extreme population growth within a brief span, and this is critical for their continued transmission and a contributing factor for their pathogenesis in the host. As with other eukaryotes, successful mitosis is an essential requirement for Plasmodium reproduction; however, some aspects of Plasmodium mitosis are quite distinct and not fully understood. In this review, we will discuss the current understanding of the architecture and key events of mitosis in Plasmodium falciparum and related parasites and compare them with the traditional mitotic events described for other eukaryotes.     

A study on pathogenicity and mosquito transmission success in the rodent malaria parasite Plasmodium chabaudi adami

We investigated the parasitology, pathogenicity (virulence) and infectivity to mosquitoes of blood infections in mice, of two strains, DS and DK, of the rodent malaria parasite Plasmodium chabaudi adami. Blood infections of DS were found to be highly pathogenic; the asexual parasites in these infections were fast-growing and showed no evidence of selectivity in their infection of host erythrocytes. In contrast to DS, blood infections of DK were much less pathogenic; the asexual parasites were slower-growing and showed a moderate degree of selectivity to a subset of erythrocytes which were not reticulocytes. In both DS and DK infections, infectivity to mosquitoes was highest before the peak of asexual parasitaemia had occurred; usually this did not coincide with the time when gametocyte numbers in the blood were highest. Infections with the pathogenic DS strain in CBA mice produced fewer gametocytes than did the less pathogenic DK strain. The DS strain infections in both CBA and C57 mice were also significantly much less infective to mosquitoes than the DK strain. Investigations by others on the related rodent malaria parasite subspecies, Plasmodium chabaudi chabaudi, have indicated that the mosquito infectivity of blood infections in mice tended to be higher in the more pathogenic (virulent) and lower in the less pathogenic strains of this parasite subspecies. This is the converse of the finding of the present investigation of blood infections of P. c. adami in mice in which a more pathogenic, or virulent, strain (DS) of these parasites was significantly much less infective to mosquitoes than was a less pathogenic strain (DK).     

The heat shock protein 40 family of the malaria parasite Plasmodium falciparum

Few diseases have had such a profound influence on human evolution and history as malaria. Despite intense efforts malaria infection continues to be a major killer. The causative agent of malaria, the unicellular eukaryote Plasmodium, displays a fascinating biology in which ubiquitous cellular concepts are modified to serve the particular needs of the malaria parasite. In this review, we explore how Plasmodium utilizes the heat shock protein 40 system, a chaperone system that ensures correct protein folding under normal and stress conditions. We highlight the peculiarities of the Plasmodium system and discuss whether any components of the system might be exploited for intervention strategies against this debilitating disease.     

Unraveling the components of protein translocation pathway in human malaria parasite Plasmodium falciparum

The targeting and translocation of proteins is an essentially required and conserved process in all the living organisms. This complex process involves multiple steps and requires a variety of factors before the protein reaches its final destination. The major components of translocation machinery are signal recognition particle (SRP) and secretory (Sec) complex. These are composed of highly conserved components. SRP contains SRP RNA and other polypeptides such as SRP9, SRP14, SRP19 and SRP54. Sec complex is composed of Sec61αβγ, Sec62 and Sec63. In this review using bioinformatics approach we have shown that the P. falciparum genome contains the homologues for all of these and other factors such as SRP receptor, and TRAM (translocation associated membrane protein), which are required for post- and co-translational protein translocation. We have also shown the various steps of translocation in a hypothetical model.     

Compensatory evolution in the human malaria parasite Plasmodium ovale

The fixation of neutral compensatory mutations in a population depends on the effective population size of the species, which can fluctuate dramatically within a few generations, the mutation rate, and the selection intensity associated with the individual mutations. We observe compensatory mutations and intermediate states in populations of the malaria parasite Plasmodium ovale. The appearance of compensatory mutations and intermediate states in P. ovale raises interesting questions about population structure that could have considerable impact on the control of the associated disease.     

Proteomics of the human malaria parasite Plasmodium falciparum

The lethal species of malaria parasite, Plasmodium falciparum, continues to exact a huge toll of mortality and morbidity, particularly in sub-Saharan Africa. Completion of the genome sequence of this organism and advances in proteomics and mass spectrometry have opened up unprecedented opportunities for understanding the complex biology of this parasite and how it responds to drug challenge and other interventions. This review describes recent progress that has been made in applying proteomics technology to this important pathogen and provides a look forward to likely future developments.     

Selection for high and low virulence in the malaria parasite Plasmodium chabaudi.

What stops parasites becoming ever more virulent? Conventional wisdom and most parasite-centred models of the evolution of virulence suppose that risk of host (and, hence, parasite) death imposes selection against more virulent strains. Here we selected for high and low virulence within each of two clones of the rodent malaria parasite Plasmodium chabaudi on the basis of between-host differences in a surrogate measure of virulence--loss of live weight post-infection. Despite imposing strong selection for low virulence which mimicked 50-75% host mortality, the low virulence lines increased in virulence as much as the high virulence lines. Thus, artificial selection on between-host differences in virulence was unable to counteract natural selection for increased virulence caused by within-host selection processes. The parasite''s asexual replication rate and number of sexual transmission forms also increased in all lines, consistent with evolutionary models explaining high virulence. An upper bound to virulence, though not the asexual replication rate, was apparent, but this bound was not imposed by host mortality. Thus, we found evidence of the factors assumed to drive evolution of increased virulence, but not those thought to counter this selection.     

Vitamin B6 biosynthesis by the malaria parasite Plasmodium falciparum: biochemical and structural insights

Vitamin B6 is one of nature's most versatile cofactors. Most organisms synthesize vitamin B6 via a recently discovered pathway employing the proteins Pdx1 and Pdx2. Here we present an in-depth characterization of the respective orthologs from the malaria parasite, Plasmodium falciparum. Expression profiling of Pdx1 and -2 shows that blood-stage parasites indeed possess a functional vitamin B6 de novo biosynthesis. Recombinant Pdx1 and Pdx2 form a complex that functions as a glutamine amidotransferase with Pdx2 as the glutaminase and Pdx1 as pyridoxal-5 '-phosphate synthase domain. Complex formation is required for catalytic activity of either domain. Pdx1 forms a chimeric bi-enzyme with the bacterial YaaE, a Pdx2 ortholog, both in vivo and in vitro, although this chimera does not attain full catalytic activity, emphasizing that species-specific structural features govern the interaction between the protein partners of the PLP synthase complexes in different organisms. To gain insight into the activation mechanism of the parasite bi-enzyme complex, the three-dimensional structure of Pdx2 was determined at 1.62 A. The obstruction of the oxyanion hole indicates that Pdx2 is in a resting state and that activation occurs upon Pdx1-Pdx2 complex formation.     

Polyamine synthesis and salvage pathways in the malaria parasite Plasmodium falciparum

We demonstrate, for the first time, a functional polyamine biosynthetic pathway in the malaria parasite Plasmodium falciparum that culminates in the synthesis of spermine. Additionally, we also report putrescine and spermidine salvage in the malaria parasite. Putrescine and spermidine transport in P. falciparum infected red blood cells is a highly specific, carrier mediated and active process, mediated by new transporters that differ from the transporters of uninfected red blood cells in their kinetic parameters, Vmax and km, as well as in their activation energy.     

Adenylyl and guanylyl cyclases from the malaria parasite Plasmodium falciparum

Completion of several malaria parasite genome sequences and advances in Plasmodium gene manipulation technology, will lead to significant advances in our knowledge of the biology of these organisms. Biochemical analysis of the cyclic nucleotide signalling pathways of P. falciparum has provided important information on malaria parasite development. The Plasmodium purine nucleotide cyclase enzymes have extremely unusual structures and the regulatory mechanisms controlling parasite enzyme activity are distinct from those operating on the analogous host molecules. Study of these enzymes could therefore lead to novel strategies for anti-malarial intervention in addition to providing unique insights into the intriguing biology of the parasite.     

Extensive microsatellite diversity in the human malaria parasite Plasmodium vivax

The population structure of Plasmodium vivax remains elusive. The markers of choice for large-scale population genetic studies of eukaryotes, short tandem repeats known as microsatellites, have been recently reported to be less polymorphic in P. vivax. Here we investigate the microsatellite diversity and geographic structure in P. vivax, at both local and global levels, using 14 new markers consisting of tri- or tetranucleotide repeats. The local-level analysis, which involved 50 field isolates from Sri Lanka, revealed unexpectedly high diversity (average virtual heterozygosity [H(E)], 0.807) and significant multilocus linkage disequilibrium in this region of low malaria endemicity. Multiple-clone infections occurred in 60% of isolates sampled in 2005. The global-level analysis of field isolates or monkey-adapted strains identified 150 unique haplotypes among 164 parasites from four continents. Individual P. vivax isolates could not be unambiguously assigned to geographic populations. For example, we found relatively low divergence among parasites from Central America, Africa, Southeast Asia and Oceania, but substantial differentiation between parasites from the same continent (South Asia and Southeast Asia) or even from the same country (Brazil). Parasite relapses, which may extend the duration of P. vivax carriage in humans, are suggested to facilitate the spread of strains across continents, breaking down any pre-existing geographic structure.     

Transfection of the human malaria parasite Plasmodium falciparum.

In the past few years, methods have been developed which allow the introduction of exogenous DNA into the human malaria parasite Plasmodium falciparum. This important technical advance known as parasite transfection, provides powerful new tools to study the function of Plasmodium proteins and their roles in biology and disease. Already it has allowed the analysis of promoter function and has been successfully applied to establish the role of particular molecules and/or mutations in the biology of this parasite. This review summarises the current state of the technology and how it has been applied to dissect the function of the P. falciparum genome.     

Recombinant human antibodies specific for the Pfs48/45 protein of the malaria parasite Plasmodium falciparum

We report the first construction of two combinatorial human phage display libraries derived from malaria-immune patients. Specific single-chain Fv fragments (scFv) against Pfs48/45, a gamete surface protein of the sexual stages of Plasmodium falciparum, were selected and analyzed extensively. The selected scFv reacted with the surface of extracellular sexual forms of the parasite and showed Pfs48/45 reactivity on immunoblot. The scFv inhibit binding of human malaria sera to native Pfs48/45 from gametocytes. Moreover, the scFv bind to target epitopes of Pfs48/45 exposed in natural infections. Sequence analysis of eight scFv clones specific for epitope III of Pfs48/45 revealed that these clones could be divided into one V(H) family-derived germ-line gene (V(H)1) and two V(L) family segments (V(L)2 and V(K)I).