A postgenomic view of the heat shock proteins in kinetoplastids

Phosphoproteomic analysis of wild-type and antimony-resistant Leishmania braziliensis lines by 2D-DIGE technology

Protein phosphorylation is one of the most studied post-translational modifications that is involved in different cellular events in Leishmania. In this study, we performed a comparative phosphoproteomics analysis of potassium antimonyl tartrate (SbIII)-resistant and -susceptible lines of Leishmania braziliensis using a 2D-DIGE approach followed by MS. In order to investigate the differential phosphoprotein abundance associated with the drug-induced stress response and SbIII-resistance mechanisms, we compared nontreated and SbIII-treated samples of each line. Pair wise comparisons revealed a total of 116 spots that showed a statistically significant difference in phosphoprotein abundance, including 11 and 34 spots specifically correlated with drug treatment and resistance, respectively. We identified 48 different proteins distributed into seven biological process categories. The category "protein folding/chaperones and stress response" is mainly implicated in response to SbIII treatment, while the categories "antioxidant/detoxification," "metabolic process," "RNA/DNA processing," and "protein biosynthesis" are modulated in the case of antimony resistance. Multiple sequence alignments were performed to validate the conservation of phosphorylated residues in nine proteins identified here. Western blot assays were carried out to validate the quantitative phosphoproteome analysis. The results revealed differential expression level of three phosphoproteins in the lines analyzed. This novel study allowed us to profile the L. braziliensis phosphoproteome, identifying several potential candidates for biochemical or signaling networks associated with antimony resistance phenotype in this parasite.

A touch of Zen: post-translational regulation of the Leishmania stress response

Across bacterial, archaeal and eukaryotic kingdoms, heat shock proteins (HSPs) are defined as a class of highly conserved chaperone proteins that are rapidly induced in response to temperature increase through dedicated heat shock transcription factors. While this transcriptional response governs cellular adaptation of fungal, plant and animal cells to thermic shock and other forms of stress, early-branching eukaryotes of the kinetoplastid order, including trypanosomatid parasites, lack classical mechanisms of transcriptional regulation and show largely constitutive expression of HSPs, thus raising important questions on the function of HSPs in the absence of stress and the regulation of their chaperone activity in response to environmental adversity. Understanding parasite-specific mechanisms of stress-response regulation is especially relevant for protozoan parasites of the genus Leishmania that are adapted for survival inside highly toxic phagolysosomes of host macrophages causing the various immuno-pathologies of leishmaniasis. Here we review recent advances on the function and regulation of chaperone activities in these kinetoplastid pathogens and propose a new model for stress-response regulation through a reciprocal regulatory relationship between stress kinases and chaperones that may be relevant for parasite-adaptive differentiation and infectivity.

Mitochondrial heat shock protein machinery hsp70/hsp40 is indispensable for proper mitochondrial DNA maintenance and replication

Mitochondrial chaperones have multiple functions that are essential for proper functioning of mitochondria. In the human-pathogenic protist Trypanosoma brucei, we demonstrate a novel function of the highly conserved machinery composed of mitochondrial heat shock proteins 70 and 40 (mtHsp70/mtHsp40) and the ATP exchange factor Mge1. The mitochondrial DNA of T. brucei, also known as kinetoplast DNA (kDNA), is represented by a single catenated network composed of thousands of minicircles and dozens of maxicircles packed into an electron-dense kDNA disk. The chaperones mtHsp70 and mtHsp40 and their cofactor Mge1 are uniformly distributed throughout the single mitochondrial network and are all essential for the parasite. Following RNA interference (RNAi)-mediated depletion of each of these proteins, the kDNA network shrinks and eventually disappears. Ultrastructural analysis of cells depleted for mtHsp70 or mtHsp40 revealed that the otherwise compact kDNA network becomes severely compromised, a consequence of decreased maxicircle and minicircle copy numbers. Moreover, we show that the replication of minicircles is impaired, although the lack of these proteins has a bigger impact on the less abundant maxicircles. We provide additional evidence that these chaperones are indispensable for the maintenance and replication of kDNA, in addition to their already known functions in Fe-S cluster synthesis and protein import.

Impairment or loss of mitochondrial DNA is associated with mitochondrial dysfunction and a wide range of neural, muscular, and other diseases. We present the first evidence showing that the entire mtHsp70/mtHsp40 machinery plays an important role in mitochondrial DNA replication and maintenance, a function likely retained from prokaryotes. These abundant, ubiquitous, and multifunctional chaperones share phenotypes with enzymes engaged in the initial stages of replication of the mitochondrial DNA in T. brucei.

Mitochondrial heat shock protein machinery hsp70/hsp40 is indispensable for proper mitochondrial DNA maintenance and replication

Mitochondrial chaperones have multiple functions that are essential for proper functioning of mitochondria. In the human-pathogenic protist Trypanosoma brucei, we demonstrate a novel function of the highly conserved machinery composed of mitochondrial heat shock proteins 70 and 40 (mtHsp70/mtHsp40) and the ATP exchange factor Mge1. The mitochondrial DNA of T. brucei, also known as kinetoplast DNA (kDNA), is represented by a single catenated network composed of thousands of minicircles and dozens of maxicircles packed into an electron-dense kDNA disk. The chaperones mtHsp70 and mtHsp40 and their cofactor Mge1 are uniformly distributed throughout the single mitochondrial network and are all essential for the parasite. Following RNA interference (RNAi)-mediated depletion of each of these proteins, the kDNA network shrinks and eventually disappears. Ultrastructural analysis of cells depleted for mtHsp70 or mtHsp40 revealed that the otherwise compact kDNA network becomes severely compromised, a consequence of decreased maxicircle and minicircle copy numbers. Moreover, we show that the replication of minicircles is impaired, although the lack of these proteins has a bigger impact on the less abundant maxicircles. We provide additional evidence that these chaperones are indispensable for the maintenance and replication of kDNA, in addition to their already known functions in Fe-S cluster synthesis and protein import.

IMPORTANCE

Impairment or loss of mitochondrial DNA is associated with mitochondrial dysfunction and a wide range of neural, muscular, and other diseases. We present the first evidence showing that the entire mtHsp70/mtHsp40 machinery plays an important role in mitochondrial DNA replication and maintenance, a function likely retained from prokaryotes. These abundant, ubiquitous, and multifunctional chaperones share phenotypes with enzymes engaged in the initial stages of replication of the mitochondrial DNA in T. brucei.

Trypanosoma brucei J protein 2 is a stress inducible and essential Hsp40

Hsp40 proteins (also known as DnaJ or J proteins) serve as co-chaperones for Hsp70, but also display evidence of independent chaperone function. Furthermore, certain Hsp40s have been shown to be stress-inducible and essential. Trypanosomatids display a remarkable diversification of Hsp40 proteins, with numerous distinct Hsp40-like proteins encoded in the Trypanosoma brucei genome. This study investigated the role of one of the six T. brucei Type I Hsp40s, T. brucei J protein 2 (Tbj2). We found that Tbj2 was heat stress-inducible, and that knockdown using RNA interference resulted in a severe growth defect under normal growth temperatures. Furthermore, a green fluorescent protein (GFP)-Tbj2 fusion protein was found to be localized to the cytosol of T. brucei. Taken together, these data suggest that Tbj2 is not functionally equivalent to the other five Type I Hsp40s, and that it is an essential, cytosolic, and stress-inducible chaperone, potentially playing an important role in protein biogenesis in T. brucei.

Genome of the avirulent human-infective trypanosome--Trypanosoma rangeli

Background

Trypanosoma rangeli is a hemoflagellate protozoan parasite infecting humans and other wild and domestic mammals across Central and South America. It does not cause human disease, but it can be mistaken for the etiologic agent of Chagas disease, Trypanosoma cruzi. We have sequenced the T. rangeli genome to provide new tools for elucidating the distinct and intriguing biology of this species and the key pathways related to interaction with its arthropod and mammalian hosts.

Methodology/Principal Findings

The T. rangeli haploid genome is ∼24 Mb in length, and is the smallest and least repetitive trypanosomatid genome sequenced thus far. This parasite genome has shorter subtelomeric sequences compared to those of T. cruzi and T. brucei; displays intraspecific karyotype variability and lacks minichromosomes. Of the predicted 7,613 protein coding sequences, functional annotations could be determined for 2,415, while 5,043 are hypothetical proteins, some with evidence of protein expression. 7,101 genes (93%) are shared with other trypanosomatids that infect humans. An ortholog of the dcl2 gene involved in the T. brucei RNAi pathway was found in T. rangeli, but the RNAi machinery is non-functional since the other genes in this pathway are pseudogenized. T. rangeli is highly susceptible to oxidative stress, a phenotype that may be explained by a smaller number of anti-oxidant defense enzymes and heat-shock proteins.

Conclusions/Significance

Phylogenetic comparison of nuclear and mitochondrial genes indicates that T. rangeli and T. cruzi are equidistant from T. brucei. In addition to revealing new aspects of trypanosome co-evolution within the vertebrate and invertebrate hosts, comparative genomic analysis with pathogenic trypanosomatids provides valuable new information that can be further explored with the aim of developing better diagnostic tools and/or therapeutic targets.

Comparative genomics is a powerful tool that affords detailed study of the genetic and evolutionary basis for aspects of lifecycles and pathologies caused by phylogenetically related pathogens. The reference genome sequences of three trypanosomatids, T. brucei, T. cruzi and L. major, and subsequent addition of multiple Leishmania and Trypanosoma genomes has provided data upon which large-scale investigations delineating the complex systems biology of these human parasites has been built. Here, we compare the annotated genome sequence of T. rangeli strain SC-58 to available genomic sequence and annotation data from related species. We provide analysis of gene content, genome architecture and key characteristics associated with the biology of this non-pathogenic trypanosome. Moreover, we report striking new genomic features of T. rangeli compared with its closest relative, T. cruzi, such as (1) considerably less amplification on the gene copy number within multigene virulence factor families such as MASPs, trans-sialidases and mucins; (2) a reduced repertoire of genes encoding anti-oxidant defense enzymes; and (3) the presence of vestigial orthologs of the RNAi machinery, which are insufficient to constitute a functional pathway. Overall, the genome of T. rangeli provides for a much better understanding of the identity, evolution, regulation and function of trypanosome virulence determinants for both mammalian host and insect vector.

No stress--Hsp90 and signal transduction in Leishmania

SUMMARY Hsp90 (a.k.a. Hsp83) plays a significant role in the life cycle control of the protozoan parasite Leishmania donovani. Rather than protecting Leishmania spp. against adverse and stressful environs, Hsp90 is required for the maintenance of the motile, highly proliferative insect stage, the promastigote. However, Hsp90 is also essential for survival and proliferation of the intracellular mammalian stage, the amastigote. Moreover, recent evidence shows Hsp90 and other components of large multi-chaperone complexes as substrates of stage-specific protein phosphorylation pathways, and thus as likely effectors of the signal transduction pathways in Leishmania spp. Future efforts should be directed towards the identification of the protein kinases and the critical phosphorylation sites as targets for novel therapeutic approaches.

Investigating the Chaperone Properties of a Novel Heat Shock Protein, Hsp70.c, from Trypanosoma brucei

The neglected tropical disease, African Trypanosomiasis, is fatal and has a crippling impact on economic development. Heat shock protein 70 (Hsp70) is an important molecular chaperone that is expressed in response to stress and Hsp40 acts as its co-chaperone. These proteins play a wide range of roles in the cell and they are required to assist the parasite as it moves from a cold blooded insect vector to a warm blooded mammalian host. A novel cytosolic Hsp70, from Trypanosoma brucei, TbHsp70.c, contains an acidic substrate binding domain and lacks the C-terminal EEVD motif. The ability of a cytosolic Hsp40 from Trypanosoma brucei J protein 2, Tbj2, to function as a co-chaperone of TbHsp70.c was investigated. The main objective was to functionally characterize TbHsp70.c to further expand our knowledge of parasite biology. TbHsp70.c and Tbj2 were heterologously expressed and purified and both proteins displayed the ability to suppress aggregation of thermolabile MDH and chemically denatured rhodanese. ATPase assays revealed a 2.8-fold stimulation of the ATPase activity of TbHsp70.c by Tbj2. TbHsp70.c and Tbj2 both demonstrated chaperone activity and Tbj2 functions as a co-chaperone of TbHsp70.c. In vivo heat stress experiments indicated upregulation of the expression levels of TbHsp70.c.

Dealing with environmental challenges: mechanisms of adaptation in Trypanosoma cruzi

Protozoan parasites have a significant impact upon global health, infecting millions of people around the world. With limited therapeutic options and no vaccines available, research efforts are focused upon unraveling cellular mechanisms essential for parasite survival. During its life cycle, Trypanosoma cruzi, the causal agent of Chagas disease, is exposed to multiple external conditions and different hosts. Environmental cues are linked to the differentiation process allowing the parasite to complete its life cycle. Successful transmission depends on the ability of the cells to trigger adaptive responses and cope with stressors while regulating proliferation and transition to different life stages. This review focuses upon different aspects of the stress response in T. cruzi, proposing new hypotheses regarding cross-talk and cross-tolerance with respect to environmental changes and discussing open questions and future directions.

LmaPA2G4, a homolog of human Ebp1, is an essential gene and inhibits cell proliferation in L. major

We have identified LmaPA2G4, a homolog of the human proliferation-associated 2G4 protein (also termed Ebp1), in a phosphoproteomic screening. Multiple sequence alignment and cluster analysis revealed that LmaPA2G4 is a non-peptidase member of the M24 family of metallopeptidases. This pseudoenzyme is structurally related to methionine aminopeptidases. A null mutant system based on negative selection allowed us to demonstrate that LmaPA2G4 is an essential gene in Leishmania major. Over-expression of LmaPA2G4 did not alter cell morphology or the ability to differentiate into metacyclic and amastigote stages. Interestingly, the over-expression affected cell proliferation and virulence in mouse footpad analysis. LmaPA2G4 binds a synthetic double-stranded RNA polyriboinosinic polyribocytidylic acid [poly(I∶C)] as shown in an electrophoretic mobility shift assay (EMSA). Quantitative proteomics revealed that the over-expression of LmaPA2G4 led to accumulation of factors involved in translation initiation and elongation. Significantly, we found a strong reduction of de novo protein biosynthesis in transgenic parasites using a non-radioactive metabolic labeling assay. In conclusion, LmaPA2G4 is an essential gene and is potentially implicated in fundamental biological mechanisms, such as translation, making it an attractive target for therapeutic intervention.

The heat shock proteins of Trypanosoma cruzi

Trypanosoma cruzi is the causal agent of Chagas' disease, a debilitating disorder affecting millions of people in several countries. A flagellated protozoan parasite, T. cruzi has a complex life cycle that involves infecting an insect and a mammalian host. During its life cycle, the parasite undergoes several kinds of stress, prominent among which is heat stress. To deal with this environmental challenge, molecular chaperones and proteases, also known as heat shock proteins (HSPs), are induced as part of the stress response. Several families of HSPs are synthesized by T. cruzi, including members of the major HSP classes such as HSP70, HSP90, HSP100, HSP40, chaperonins and small HSPs, and these proteins show conserved and unique features. In this review we describe these proteins and the corresponding gene expression patterns and discuss their relevance to the biology of the parasite.

Evolution and species discrimination according to the Leishmania heat-shock protein 20 gene

The Leishmania genus comprises up to 35 species, of which 20 are responsible for human disease. However, the taxonomic status for many of them is under discussion. The small Heat Shock Proteins (sHSPs) are physiologically relevant, protecting cellular proteins from aggregation and maintaining cellular viability under intensive stress conditions. In Leishmania, a protein of this class was previously described, the 20-kDa heat-shock protein (HSP20), which is encoded by a single gene. In the present study, we used this target, alone or in combination with hsp70 gene, to investigate the phylogenetic relationships among Leishmania species. Using a pair of degenerate primers it was possible amplifying a 370bp fragment of the hsp20 coding region in 39 strains of very different geographic origins, representing in total 16 Leishmania species (14 if L. chagasi and L. archibaldi are considered synonymous names of L. infantum and L. donovani, respectively). Nucleotide sequences were readily obtained by direct sequencing of the amplification products. Both phylogenetic trees and networks based on either hsp20 sequences or combined datasets of hsp20 and hsp70 sequences were constructed. These phylogenic analyses supported the division of the Leishmania genus into nine species: L. (L.) donovani, L. (L.) major, L. (L.) tropica, L. (L.) aethiopica, L. (L.) mexicana, L. (V.) lainsoni, L. (V.) naiffi, L. (V.) guyanensis and L. (V.) braziliensis. Additionally, by network analysis, the subspecies L. (L.) donovani infantum and L. (V.) braziliensis peruviana were recognized within the L. (L.) donovani and L. (V.) braziliensis species, respectively. Therefore, hsp20 gene was found to be a suitable molecular marker for Leishmania typing and classification purposes. In addition, this study represents a solid contribution to the objective of establishing a more reliable taxonomy for the genus Leishmania.

Post-transcriptional regulation of the trypanosome heat shock response by a zinc finger protein

In most organisms, the heat-shock response involves increased heat-shock gene transcription. In Kinetoplastid protists, however, virtually all control of gene expression is post-transcriptional. Correspondingly, Trypanosoma brucei heat-shock protein 70 (HSP70) synthesis after heat shock depends on regulation of HSP70 mRNA turnover. We here show that the T. brucei CCCH zinc finger protein ZC3H11 is a post-transcriptional regulator of trypanosome chaperone mRNAs. ZC3H11 is essential in bloodstream-form trypanosomes and for recovery of insect-form trypanosomes from heat shock. ZC3H11 binds to mRNAs encoding heat-shock protein homologues, with clear specificity for the subset of trypanosome chaperones that is required for protein refolding. In procyclic forms, ZC3H11 was required for stabilisation of target chaperone-encoding mRNAs after heat shock, and the HSP70 mRNA was also decreased upon ZC3H11 depletion in bloodstream forms. Many mRNAs bound to ZC3H11 have a consensus AUU repeat motif in the 3'-untranslated region. ZC3H11 bound preferentially to AUU repeats in vitro, and ZC3H11 regulation of HSP70 mRNA in bloodstream forms depended on its AUU repeat region. Tethering of ZC3H11 to a reporter mRNA increased reporter expression, showing that it is capable of actively stabilizing an mRNA. These results show that expression of trypanosome heat-shock genes is controlled by a specific RNA-protein interaction. They also show that heat-shock-induced chaperone expression in procyclic trypanosome enhances parasite survival at elevated temperatures.

The Hsp90-Sti1 interaction is critical for Leishmania donovani proliferation in both life cycle stages

The heat shock protein 90 plays a pivotal role in the life cycle control of Leishmania donovani promoting the fast-growing insect stage of this parasite. Equally important for insect stage growth is the co-chaperone Sti1. We show that replacement of Sti1 is only feasible in the presence of additional Sti1 transgenes indicating an essential role. To better understand the impact of Sti1 and its interaction with Hsp90, we performed a mutational analysis of Hsp90. We established that a single amino acid exchange in the Leishmania Hsp90 renders that protein resistant to the inhibitor radicicol (RAD), yet does not interfere with its functionality. Based on this RAD-resistant Hsp90, we established a combined chemical knockout/gene complementation (CKC) approach. We can show that Hsp90 function is required in both insect and mammalian life stages and that the Sti1-binding motif of Hsp90 is crucial for proliferation of insect and mammalian stages of the parasite. The Sti1-binding motif in Leishmania Hsp90 is suboptimal - optimizing the motif increased initial intracellular proliferation underscoring the importance of the Hsp90-Sti1 interaction for this important parasitic protozoan. The CKC strategy we developed will allow the future analysis of more Hsp90 domains and motifs in parasite viability and infectivity.

17-AAG kills intracellular Leishmania amazonensis while reducing inflammatory responses in infected macrophages

Background

Leishmaniasis is a neglected endemic disease with a broad spectrum of clinical manifestations. Pentavalent antimonials have been the treatment of choice for the past 70 years and, due to the emergence of resistant cases, the efficacy of these drugs has come under scrutiny. Second-line drugs are less efficacious, cause a range of side effects and can be costly. The formulation of new generations of drugs, especially in developing countries, has become mandatory.

Methodology/Principal Findings

We investigated the anti-leishmanial effect of 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), an HSP90 inhibitor, in vitro. This inhibitor is currently in clinical trials for cancer treatment; however, its effects against intracellular Leishmania remain untested. Macrophages infected with L. amazonensis were treated with 17-AAG (25–500 nM) and parasite load was quantified using optical microscopy. Parasite load declined in 17-AAG-treated macrophages in a dose- and time-dependent manner. Intracellular parasite death became irreversible after 4 h of treatment with 17-AAG, and occurred independent of nitric oxide (NO) and superoxide (O₂⁻) production. Additionally, intracellular parasite viability was severely reduced after 48 h of treatment. Interestingly, treatment with 17-AAG reduced pro-inflammatory mediator production, including TNF-α, IL-6 and MCP-1, yet IL-12 remained unaffected. Electron microscopy revealed morphological alterations, such as double-membrane vacuoles and myelin figures at 24 and 48 h after 17-AAG treatment.

Conclusions/Significance

The HSP90 inhibitor, 17-AAG, possesses high potency under low dosage and reduces both pro-inflammatory and oxidative molecule production. Therefore, further studies are warranted to investigate this inhibitor’s potential in the development of new generations of anti-leishmanials.

Sequence analysis of the 3'-untranslated region of HSP70 (type I) genes in the genus Leishmania: its usefulness as a molecular marker for species identification

Background

The Leishmaniases are a group of clinically diverse diseases caused by parasites of the genus Leishmania. To distinguish between species is crucial for correct diagnosis and prognosis as well as for treatment decisions. Recently, sequencing of the HSP70 coding region has been applied in phylogenetic studies and for identifying of Leishmania species with excellent results.

Methods

In the present study, we analyzed the 3’-untranslated region (UTR) of Leishmania HSP70-type I gene from 24 strains representing eleven Leishmania species in the belief that this non-coding region would have a better discriminatory capacity for species typing than coding regions.

Results

It was observed that there was a remarkable degree of sequence conservation in this region, even between species of the subgenus Leishmania and Viannia. In addition, the presence of many microsatellites was a common feature of the 3´-UTR of HSP70-I genes in the Leishmania genus. Finally, we constructed dendrograms based on global sequence alignments of the analyzed Leishmania species and strains, the results indicated that this particular region of HSP70 genes might be useful for species (or species complex) typing, improving for particular species the discrimination capacity of phylogenetic trees based on HSP70 coding sequences. Given the large size variation of the analyzed region between the Leishmania and Viannia subgenera, direct visualization of the PCR amplification product would allow discrimination between subgenera, and a HaeIII-PCR-RFLP analysis might be used for differentiating some species within each subgenera.

Conclusions

Sequence and phylogenetic analyses indicated that this region, which is readily amplified using a single pair of primers from both Old and New World Leishmania species, might be useful as a molecular marker for species discrimination.

Characterization of novel Leishmania infantum recombinant proteins encoded by genes from five families with distinct capacities for serodiagnosis of canine and human visceral leishmaniasis

To expand the available panel of recombinant proteins that can be useful for identifying Leishmania-infected dogs and for diagnosing human visceral leishmaniasis (VL), we selected recombinant antigens from L. infantum, cDNA, and genomic libraries by using pools of serum samples from infected dogs and humans. The selected DNA fragments encoded homologs of a cytoplasmic heat-shock protein 70, a kinesin, a polyubiquitin, and two novel hypothetical proteins. Histidine-tagged recombinant proteins were produced after subcloning these DNA fragments and evaluated by using an enzyme-linked immunosorbent assays with panels of canine and human serum samples. The enzyme-linked immunosorbent assays with different recombinant proteins had different sensitivities (67.4-93.0% and 36.4-97.2%) and specificities (76.1-100% and 90.4-97.3%) when tested with serum samples from Leishmania-infected dogs and human patients with VL. Overall, no single recombinant antigen was sufficient to serodiagnosis all canine or human VL cases.

Hsp90: structure and function

Hsp90 is a highly abundant and ubiquitous molecular chaperone which plays an essential role in many cellular processes including cell cycle control, cell survival, hormone and other signalling pathways. It is important for the cell's response to stress and is a key player in maintaining cellular homeostasis. In the last ten years, it has become a major therapeutic target for cancer, and there has also been increasing interest in it as a therapeutic target in neurodegenerative disorders, and in the development of anti-virals and anti-protozoan infections. The focus of this review is the structural and mechanistic studies which have been performed in order to understand how this important chaperone acts on a wide variety of different proteins (its client proteins) and cellular processes. As with many of the other classes of molecular chaperone, Hsp90 has a critical ATPase activity, and ATP binding and hydrolysis known to modulate the conformational dynamics of the protein. It also uses a host of cochaperones which not only regulate the ATPase activity and conformational dynamics but which also mediate interactions with Hsp90 client proteins. The system is also regulated by post-translational modifications including phosphorylation and acetylation. This review discusses all these aspects of Hsp90 structure and function.

Toxoplasma gondii Sis1-like J-domain protein is a cytosolic chaperone associated to HSP90/HSP70 complex

Toxoplasma gondii is an obligate intracellular protozoan parasite in which 36 predicted Hsp40 family members were identified by searching the T. gondii genome. The predicted protein sequence from the gene ID TGME49_065310 showed an amino acid sequence and domain structure similar to Saccharomyces cerevisiae Sis1. TgSis1 did not show differences in its expression profile during alkaline stress by microarray analysis. Furthermore, TgSis1 showed to be a cytosolic Hsp40 which co-immunoprecipitated with T. gondii Hsp70 and Hsp90. Structural modeling of the TgSis1 peptide binding fragment revealed structural and electrostatic properties different from the experimental model of human Sis1-like protein (Hdj1). Based on these differences; we propose that TgSis1 may be a potentially attractive drug target for developing a novel anti-T. gondii therapy.

Identification of the HSP70-II gene in Leishmania braziliensis HSP70 locus: genomic organization and UTRs characterization

Background

The heat stress suffered by Leishmania sp during its digenetic life-cycle is a key trigger for its stage differentiation. In Leishmania subgenera two classes of HSP70 genes differing in their 3' UTR were described. Although the presence of HSP70-I genes was previously suggested in Leishmania (Viannia) braziliensis, HSP70-II genes had been reluctant to be uncovered.

Results

Here, we report the existence of two types of HSP70 genes in L. braziliensis and the genomic organization of the HSP70 locus. RT-PCR experiments were used to map the untranslated regions (UTR) of both types of genes. The 3' UTR-II has a low sequence identity (55-57%) when compared with this region in other Leishmania species. In contrast, the 5' UTR, common to both types of genes, and the 3' UTR-I were found to be highly conserved among all Leishmania species (77-81%). Southern blot assays suggested that L. braziliensis HSP70 gene cluster may contain around 6 tandemly-repeated HSP70-I genes followed by one HSP70-II gene, located at chromosome 28. Northern blot analysis indicated that levels of both types of mRNAs are not affected by heat shock.

Conclusions

This study has led to establishing the composition and structure of the HSP70 locus of L. braziliensis, complementing the information available in the GeneDB genome database for this species. L. braziliensis HSP70 gene regulation does not seem to operate by mRNA stabilization as occurs in other Leishmania species.

Peptide aptamer mimicking RAD51-binding domain of BRCA2 inhibits DNA damage repair and survival in Trypanosoma brucei

The eukaryotic DNA recombination repair protein BRCA2 is functional in the parasitic protozoan Trypanosoma brucei. The mechanism of the involvement of BRCA2 in homologous recombination includes its interaction with the DNA recombinase proteins of the RAD51 family. BRCA2 is known to interact with RAD51 through its unique and essential BRC sequence motifs. T. brucei BRCA2 homolog (TbBRCA2) has fifteen repeating BRC motifs as compared to mammalian BRCA2 that has only eight. We report here our yeast 2-hybrid analysis studies on the interactions of TbBRCA2 BRC motifs with five different RAD51 paralogues of T. brucei. Our study revealed that a single BRC motif is sufficient to bind to these RAD51 paralogues. To test the possibility whether a single 44 amino acid long repeating unit of the TbBRCA2 BRC motif may be exploited as an inhibitor of T. brucei growth, we ectopically expressed this peptide segment in the procyclic form of the parasite and evaluated its effects on cell survival as well as the sensitivity of these cells to the DNA damaging agent methyl methane sulfonate (MMS). Expression of a single BRC motif led to MMS sensitivity and inhibited cellular proliferation in T. brucei.

The Hsp70 chaperones of the Tritryps are characterized by unusual features and novel members

Proteins belonging to the Hsp70 class of molecular chaperones are highly conserved and ubiquitous, performing an essential role in the maintenance of cellular homeostasis in almost all known organisms. Trypanosoma brucei, Trypanosoma cruzi and Leishmania major are human parasites collectively known as the Tritryps. The Tritryps undergo extensive morphological changes during their life cycles, largely triggered by the marked differences between conditions in their insect vector and human host. Hsp70s are synthesised in response to these marked changes in environment and are proposed to be required for these parasites to successfully transition between differentiation stages while remaining viable and infective. While the Tritryps Hsp70 complement consists of homologues of all the major eukaryotic Hsp70s, there are a number of novel members, and some unique structural features. This review critically evaluates the current knowledge on the Tritryps Hsp70 proteins with an emphasis on T. brucei, and highlights some novel and previously unstudied aspects of these multifaceted molecular chaperones.

Leishmania (Viannia) braziliensis: influence of successive in vitro cultivation on the expression of promastigote proteinases

Cysteine proteinases are an important virulence factor in Leishmania parasites. In this study we analyzed the cysteine proteinase expression of infective Leishmania (Viannia) braziliensis promastigotes, examining the expression induced by successive in vitro passages in culture. We observed that this parasite presents a decrease in its virulence over BALB/c macrophages, after successive passages in culture, but still they present proteinase activity, being capable of hydrolyzing the substrate pGlu-Phe-Leu-p Nitroanilide at pH 7.0. This proteinase activity also decreases in the course of the successive passages. Additionally, the decrease in the amount of CPB proteins following successive passages of promastigotes was verified by immunoblotting assays, using an anti-CPB antiserum. Real-time PCR assays were performed to assess the relative cpb expression when compared to a housekeeping gene in promastigote cDNA preparations from the first, fourth and seventh passages. Interestingly, the data indicate a relative increase in cpb gene transcripts as the promastigotes were maintained under in vitro culture: 2.2 times higher for fourth and 2.7 times higher for seventh passages when compared to the first passage. Thus, the information gathered here shows that the expression of cysteine proteinases is modified during in vitro cultivation of L. (V.) braziliensis promastigotes.

Trypanosoma cruzi: modulation of HSP70 mRNA stability by untranslated regions during heat shock

Gene regulation in trypanosomatids occurs mainly by post-transcriptional mechanisms modulating mRNA stability and translation. We have investigated heat shock protein (HSP) 70 gene regulation in Trypanosoma cruzi, the causal agent of Chagas' disease. The HSP70 mRNA's half-life increases after heat shock, and the stabilization is dependent on protein synthesis. In a cell-free RNA decay assay, a U-rich region in the 3' untranslated region (UTR) is a target for degradation, which is reduced when in the presence of protein extracts from heat shocked cells. In a transfected reporter gene assay, both the 5'- and 3'-UTRs confer temperature-dependent regulation. Both UTRs must be present to increase mRNA stability at 37 degrees C, indicating that the 5'- and 3'-UTRs act cooperatively to stabilize HSP70 mRNA during heat shock. We conclude that HSP70 5'- and 3'-UTRs regulate mRNA stability during heat shock in T. cruzi.

Phosphoproteome dynamics reveal heat-shock protein complexes specific to the Leishmania donovani infectious stage

Leishmania is exposed to a sudden increase in environmental temperature during the infectious cycle that triggers stage differentiation and adapts the parasite phenotype to intracellular survival in the mammalian host. The absence of classical promoter-dependent mechanisms of gene regulation and constitutive expression of most of the heat-shock proteins (HSPs) in these human pathogens raise important unresolved questions as to regulation of the heat-shock response and stage-specific functions of Leishmania HSPs. Here we used a gel-based quantitative approach to assess the Leishmania donovani phosphoproteome and revealed that 38% of the proteins showed significant stage-specific differences, with a strong focus of amastigote-specific phosphoproteins on chaperone function. We identified STI1/HOP-containing chaperone complexes that interact with ribosomal client proteins in an amastigote-specific manner. Genetic analysis of STI1/HOP phosphorylation sites in conditional sti1(-/-) null mutant parasites revealed two phosphoserine residues essential for parasite viability. Phosphorylation of the major Leishmania chaperones at the pathogenic stage suggests that these proteins may be promising drug targets via inhibition of their respective protein kinases.

Phylogeny of Leishmania species based on the heat-shock protein 70 gene

The 70kDa heat-shock protein (HSP70) is conserved across prokaryotes and eukaryotes, and the protein as well as its encoding gene have been applied in phylogenetic studies of different parasites. In spite of the frequent use of New World Leishmania species identification on the basis of restriction fragment length polymorphisms (RFLP) in the hsp70 gene, it was never sequenced extensively for studying evolutionary relationships. To fill this void we determined the nucleotide sequence of an 1380bp fragment of the coding region commonly used in RFLP analysis, from 43 isolates and strains of different geographic origins. Combination with previously determined sequences amounted to a phylogenetic analysis including 52 hsp70 sequences representing 17 species commonly causing leishmaniasis both in the New and Old World. The genus Leishmania formed a monophyletic group with three distinct subgenera L. (Leishmania), L. (Viannia), and L. (Sauroleishmania). The obtained phylogeny supports the following eight species: L. (L.) donovani, L. (L.) major, L. (L.) tropica, L. (L.) mexicana, L. (V.) lainsoni, L. (V.) naiffi, L. (V.) guyanensis and L. (V.) braziliensis, in some of which subspecies can be recognized: L. (L.) donovani infantum, L. (V.) guyanensis panamensis, and L. (V.) braziliensis peruviana. The currently recognized L. (L.) aethiopica, L. (L.) garnhami, and L. (L.) amazonensis did not form monophyletic clusters. These findings are discussed in relation to results from other genes and proteins, which have to be integrated in order to build a genetically supported taxonomy for the entire genus.

Sequence analysis and PCR-RFLP profiling of the hsp70 gene as a valuable tool for identifying Leishmania species associated with human leishmaniasis in Brazil

Since the first report of the genus Leishmania, many species have been described. In Brazil, human leishmaniasis has been associated with eight Leishmania species, of which seven are responsible for cutaneous leishmaniasis (CL). In some endemic areas, CL is associated with only one species; however, in other areas, such as the Amazon, the etiology of CL can be assigned to many species. The multitude of highly similar Leishmania species in Brazil makes it difficult to develop an appropriate method of typing them. Most Leishmania species were first described based on epidemiological and biological characteristics, and these were later corroborated by Multilocus Enzyme Electrophoresis (MLEE), the gold standard technique for identifying Leishmania species. In an attempt to overcome the limitations of MLEE, many PCR-based methods have been developed and used for parasite identification. In the present study, we analyzed the sequence of the hsp70 gene in Leishmania species associated with human leishmaniasis in Brazil. This analysis led to the identification of restriction enzymes that could be used for PCR-RFLP-based identification. The results obtained were in complete agreement with those obtained by MLEE, suggesting that PCR-RFLP analysis of hsp70 could soon replace MLEE for routine Leishmania typing.

Overproduction, purification and characterisation of Tbj1, a novel Type III Hsp40 from Trypanosoma brucei, the African sleeping sickness parasite

The heat shock protein 40 (Hsp40) family of proteins act as co-chaperones of the heat shock protein 70 (Hsp70) chaperone family, and together they play a vital role in the maintenance of cellular homeostasis. The Type III class of Hsp40s are diverse in terms of both sequence identity and function and have not been extensively characterised. The Trypanosoma brucei parasite is the causative agent of Human African Trypanosomiasis, and possesses an unusually large Hsp40 complement, consisting mostly of Type III Hsp40s. A novel T. brucei Type III Hsp40, Tbj1, was heterologously expressed, purified, and found to exist as a compact monomer in solution. Using polyclonal antibodies to the full-length recombinant protein, Tbj1 was found by Western analysis to be expressed in the T. brucei bloodstream-form. Tbj1 was found to be able to assist two different Hsp70 proteins in the suppression of protein aggregation in vitro, despite being unable to stimulate their ATPase activity. This indicated that while Tbj1 did not possess independent chaperone activity, it potentially functioned as a novel co-chaperone of Hsp70 in T. brucei.

Trypanosoma carassii hsp70 increases expression of inflammatory cytokines and chemokines in macrophages of the goldfish (Carassius auratus L.)

We report on the cloning and characterization of Trypanosoma carassii 70 KDa heat shock protein (hsp70). T. carassii hsp70 was secreted/excreted into culture medium in vitro and was recognized by sera from infected fish. Recombinant hsp70 (rhsp70) activated goldfish macrophages and stimulated the production of pro-inflammatory cytokines including interferon gamma (IFNgamma), tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, (IL)-12 and chemokines CCL-1 and CXCL-8 (IL-8). T. carassii hsp70-induced cytokine expression was abrogated by pronase treatment of macrophages confirming the existence of receptor(s) on goldfish macrophage surface that recognize parasite molecule. Parasite hsp70 also up-regulated the expression inducible nitric oxide synthase (iNOS) isoforms A and B and induced a strong nitric oxide response of goldfish macrophages.

Heat shock causes a decrease in polysomes and the appearance of stress granules in trypanosomes independently of eIF2(alpha) phosphorylation at Thr169

In trypanosomes there is an almost total reliance on post-transcriptional mechanisms to alter gene expression; here, heat shock was used to investigate the response to an environmental signal. Heat shock rapidly and reversibly induced a decrease in polysome abundance, and the consequent changes in mRNA metabolism were studied. Both heat shock and polysome dissociation were necessary for (1) a reduction in mRNA levels that was more rapid than normal turnover, (2) an increased number of P-body-like granules that contained DHH1, SCD6 and XRNA, (3) the formation of stress granules that remained largely separate from the P-body-like granules and localise to the periphery of the cell and, (4) an increase in the size of a novel focus located at the posterior pole of the cell that contain XRNA, but neither DHH1 nor SCD6. The response differed from mammalian cells in that neither the decrease in polysomes nor stress-granule formation required phosphorylation of eIF2alpha at the position homologous to that of serine 51 in mammalian eIF2alpha and in the occurrence of a novel XRNA-focus.

Stress response pathways in protozoan parasites

Diseases caused by protozoan parasites have a dramatic impact on world health. Emerging drug resistance and a general lack of experimental understanding has created a void in the medicine cabinet used to treat these widespread infections. A novel therapeutic idea that is receiving more attention is centred on targeting the microbe's response to the multitude of environmental stresses it encounters. Protozoan pathogens have complex life cycles, often having to transition from one host to another, or survive in a cyst form in the environment until a new host arrives. The need to respond to environmental cues and stress, and endure in less than optimal conditions, is paramount to their viability and successful progression through their life cycle. This review summarizes the research on parasitic stress responses for Apicomplexa, kinetoplastids and anaerobic protozoa, with an eye towards how these processes may be exploited therapeutically.

Distinct mitochondrial HSP70 homologues conserved in various Leishmania species suggest novel biological functions

We report the identification of two distinct homologues of the 70-kDa mitochondrial heat shock protein (mtHSP70) from Leishmania chagasi/Leishmania infantum (Lc2.1 and Lc2.2). In Leishmania species, multiple genes encoding Lc2.2 are present whilst single genes encode Lc2.1. Strikingly, genes encoding Lc2.1-like proteins are absent from Trypanosoma species. Lc2.2 is characterized by a poly-glutamine rich C-terminus, absent from Lc2.1 or mtHSP70 homologues outside the trypanosomatids. Lc2.1 displays unique substitutions within its peptide-binding domain which modify amino acids strictly conserved in cytoplasmic and mitochondrial HSP70 proteins alike. Affinity purified antibodies recognize mainly a single protein in extracts from promastigotes/epimastigotes of various Leishmania/Trypanosoma species. Upon differentiation of Leishmania amazonensis into amastigotes a second protein (presumably Lc2.1) is induced and becomes the predominant mtHSP70 homologue expressed. Subcellular localization of these proteins was investigated and ratified a distribution throughout the mitochondrial matrix. Our results imply novel mtHSP70 functions which evolved within the genus Leishmania.

Phosphoproteomic analysis of Leishmania donovani pro- and amastigote stages

Following transmission to the vertebrate host, the protozoan parasite Leishmania donovani differentiates into the pathogenic amastigote stage that is adapted for intracellular survival. This developmental transition is induced by environmental factors including elevated temperature and acidic pH and is likely transduced by signaling cascades involving protein kinases and their downstream phosphoprotein substrates. These signaling networks are highly adapted to the specific nutritional and physiological requirements of the organism and thus studying Leishmania phosphorylation may allow important insight into the parasite-specific biology. We used a gel-based approach to investigate qualitative and quantitative changes of the phosphoproteome of the major L. donovani life cycle stages. Phosphoproteins were purified by immobilized metal affinity chromatography (IMAC), separated by IEF and SDS-PAGE using pH 4-7 IPG immobiline strips, revealed by fluorescent multiplex staining, and identified by MALDI-MS and MS/MS. Our analysis allowed us to establish a first repertoire of the Leishmania phosphoproteome and to identify phosphoproteins implicated in stress- and heat shock response, RNA/protein turnover, metabolism, and signaling.

Protein phosphatase 5 is required for Hsp90 function during proteotoxic stresses in Trypanosoma brucei

Trypanosoma brucei, a parasitic protozoan that causes African trypanosomiasis in human and domestic animals, adapt in various environments during their digenetic life cycle. In this study, we found that Hsp90 is crucial for the survival of this parasite. Inhibition of Hsp90 activity by geldanamycin (GA) reduced cell growth and increased the level of Hsp90. Both the bloodstream and procyclic forms of T. brucei showed a several-fold greater sensitivity than the mammalian cells to GA and also to 17-AAG, a less toxic derivative of GA, suggesting that Hsp90 could be a potential chemotherapeuric target for African trypanosomiasis. T. brucei Hsp90 interacts with the protein phosphatase 5 (PP5) in vivo. Under normal growth conditions, T. brucei PP5 (TbPP5) and Hsp90 are primarily localized in the cytosol. However, with increase in growth temperature and GA treatment, these proteins translocate to the nucleus. Overproduction of TbPP5 by genetic manipulation reduced the growth inhibitory effect of GA, while knockdown of TbPP5 reduced cell growth more in the presence of GA, as compared to parental control. Depletion of TbPP5, however, did not prevent the induction of Hsp90 protein level during GA treatment. Together, these results suggest that TbPP5 positively regulates the function of Hsp90 to maintain cellular homeostasis during proteotoxic stresses in T. brucei.