Molecular cloning of a Trypanosoma cruzi cDNA encoding a protein homologous with mammalian elongation factor 1 beta

Comparative protein profiling identifies elongation factor-1β and tryparedoxin peroxidase as factors associated with metastasis in Leishmania guyanensis

Parasites of the Leishmania Viannia subgenus are major causative agents of mucocutaneous leishmaniasis (MCL), a disease characterised by parasite dissemination (metastasis) from the original cutaneous lesion to form debilitating secondary lesions in the nasopharyngeal mucosa. We employed a protein profiling approach to identify potential metastasis factors in laboratory clones of L. (V.) guyanensis with stable phenotypes ranging from highly metastatic (M+) through infrequently metastatic (M+/M-) to non-metastatic (M-). Comparison of the soluble proteomes of promastigotes by two-dimensional electrophoresis revealed two abundant protein spots specifically associated with M+ and M+/M- clones (Met2 and Met3) and two others exclusively expressed in M- parasites (Met1 and Met4). The association between clinical disease phenotype and differential expression of Met1-Met4 was less clear in L. Viannia strains from mucosal (M+) or cutaneous (M-) lesions of patients. Identification of Met1-Met4 by biological mass spectrometry (LC-ES-MS/MS) and bioinformatics revealed that M+ and M- clones express distinct acidic and neutral isoforms of both elongation factor-1 subunit beta (EF-1beta) and cytosolic tryparedoxin peroxidase (TXNPx). This interchange of isoforms may relate to the mechanisms by which the activities of EF-1beta and TXNPx are modulated, and/or differential post-translational modification of the gene product(s). The multiple metabolic functions of EF-1 and TXNPx support the plausibility of their participation in parasite survival and persistence and thereby, metastatic disease. Both polypeptides are active in resistance to chemical and oxidant stress, providing a basis for further elucidation of the importance of antioxidant defence in the pathogenesis underlying MCL.

Trypanothione S-transferase activity in a trypanosomatid ribosomal elongation factor 1B

Trypanothione is a thiol unique to the Kinetoplastida and has been shown to be a vital component of their antioxidant defenses. However, little is known as to the role of trypanothione in xenobiotic metabolism. A trypanothione S-transferase activity was detected in extracts of Leishmania major, L. infantum, L. tarentolae, Trypanosoma brucei, and Crithidia fasciculata, but not Trypanosoma cruzi. No glutathione S-transferase activity was detected in any of these parasites. Trypanothione S-transferase was purified from C. fasciculata and shown to be a hexadecameric complex of three subunits with a relative molecular weight of 650,000. This enzyme complex was specific for the thiols trypanothione and glutathionylspermidine and only used 1-chloro-2,4-dinitrobenzene from a range of glutathione S-transferase substrates. Peptide sequencing revealed that the three components were the alpha, beta, and gamma subunits of ribosomal eukaryotic elongation factor 1B (eEF1B). Partial dissociation of the complex suggested that the S-transferase activity was associated with the gamma subunit. Moreover, Cibacron blue was found to be a tight binding inhibitor and reactive blue 4 an irreversible time-dependent inhibitor that covalently modified only the gamma subunit. The rate of inactivation by reactive blue 4 was increased more than 600-fold in the presence of trypanothione, and Cibacron blue protected the enzyme from inactivation by 1-chloro-2,4-dinitrobenzene, confirming that these dyes interact with the active site region. Two eEF1Bgamma genes were cloned from C. fasciculata, but recombinant C. fasciculata eEF1Bgamma had no S-transferase activity, suggesting that eEF1Bgamma is unstable in the absence of the other subunits.

Glutathione S-transferases and related proteins from pathogenic human parasites behave as immunomodulatory factors

There is a rapidly expanding interest into the glutathione S-transferases (GSTs) and the structurally related molecules. Many of the latter have been identified as members of conserved protein families sharing structural and some times functional properties being particularly involved in heat-shock response, drug resistance and carcinogenesis. Also, evidence is emerging that members of the GST super family from some pathogens could exert immunomodulatory functions toward the cell of the immune system, involving separate profiles of cytokine gene transcription and different patterns of cell growth, illustrating therefore the 'one gene-dual function' phenomenon. The implication of these biological properties for pathogenesis is discussed.

Cloning of a Leishmania major gene encoding for an antigen with extensive homology to ribosomal protein S3a

Following purification by affinity chromatography, a Leishmania major S-hexylglutathione- binding protein of molecular mass 66kDa was isolated. The immune serum against the parasite 66kDa polypeptide when used to screen a L. major cDNA library could identify clones encoding for the human v-fos transformation effector homologue, namely ribosomal protein S3a, and thus was named LmS3a-related protein (LmS3arp). A 1027bp cDNA fragment was found to contain the entire parasite gene encoding for a highly basic protein of 30kDa calculated molecular mass sharing homology to various ribosomal S3a proteins from different species. Using computer methods for a multiple alignment and sequence motif search, we found that LmS3arp shares a sequence homology to class theta glutathione S-transferase mainly in a segment containing critical residues involved in glutathione binding. These new findings are discussed in the light of recent published data showing multiple function(s) of the ribosomal proteins S3a.

Phenotype of recombinant Trypanosoma cruzi which overexpress elongation factor 1-gamma: possible involvement of EF-1gamma GST-like domain in the resistance to clomipramine

In previous studies, molecular and immunological approaches have been used to characterize the Trypansosoma cruzi elongation factor 1gamma (TcEF-1gamma). A primary sequence homology search revealed that the TcEF-1gamma N-terminal domain showed significant homology to glutathione S-transferases (GSTs). Although studies have suggested the involvement of EF-1gamma in the protein synthesis machinery, the exact function of this protein, particularly the role of its GST-like domain, is not fully understood. Therefore, we have used the protozoan parasite T. cruzi, as a recipient for a shuttle vector which allows overexpression of TcEF-1gamma in order to gain insight into its biological function. The growth of parasites which overexpress TcEF-1gamma and control cells was equally sensitive to inhibition by nifurtimox and benznidazole, which exert a trypanocidal activity through the production of free radicals. In contrast, a strong resistance of transformed organisms to the tricyclic antidepressant drug, clomipramine, a lipophilic compound, was observed, whereas control cells were highly sensitive. Our findings suggest that TcEF-1gamma participates in the detoxification of lipophilic compounds probably by conjugation with glutathione through its GST-like domain. To our knowledge, this is the first report showing that the eukaryotic EF-1gamma GST conserved enzymatic model could play a role in drug resistance. Furthermore, these results reinforce the notion that the aggressiveness of certain tumours could in part be linked to overexpression of EF-1gamma. They also raise a central question regarding the GST as target for chemotherapeutic drugs in cancer research.

Trypanosoma cruzi elongation factor 1-alpha: nuclear localization in parasites undergoing apoptosis

The cloning and sequencing of the gene coding for Trypanosoma cruzi elongation factor 1 alpha (TcEF-1 alpha) was performed by screening a T. cruzi genomic library with a probe obtained through the polymerase chain reaction (PCR) amplification of T. cruzi DNA using two oligonucleotides deduced from the sequence of T. brucei EF-1 alpha. Southern blot analysis of T. cruzi digested genomic DNA and Northern blot hybridized with the labeled probe revealed that one copy of TcEF-1 alpha exist in the genome of the parasite. Indirect immunofluorescence technique using anti-EF-1 alpha antibodies and epimastigotes harvested after different days of in vitro culture showed that EF-1 alpha is localised in the cytoplasm of the parasites from the exponential growth phase. Surprisingly, during the stationary phase (ageing parasites), EF-1 alpha was found in the nucleus. Furthermore, treatment of parasites with the antibiotic drug geneticin (G418) which induces the death of epimastigotes by apoptosis showed selective localization of EF-1 alpha in the nucleus of dying parasites. This observation supports the notion already reported in the case of mammalian cells that EF-1 alpha could participate in the transcription processes and possibly in the case of T. cruzi, in the expression regulation of genes involved in the control of cell death. The possible transfection and genomic manipulation of T. cruzi may provide a model to study the role of TcEF-1 alpha in this phenomenon.

Archaeal elongation factor 1 beta is a dimer. Primary structure, molecular and biochemical properties

The elongation factor 1 beta (EF-1 beta), that in eukarya and archaea promotes the replacement of GDP by GTP on the elongation factor 1 alpha x GDP complex, was purified to homogeneity from the thermoacidophilic archaeon Sulfolobus solfataricus (SsEF-1 beta). Its primary structure was established by sequenced Edman degradation of the entire protein or its proteolytic peptides. The molecular weight of SsEF-1 beta was estimated as about 10000 or 20000 under denaturing or native conditions respectively; this finding suggests that the native protein exists as a dimer. The peptide chain of SsEF-1 beta is much shorter than that of its eukaryotic analogues and homology is found only at their C-terminal region; no homology exists between SsEF-1 beta and eubacterial EF-Ts. At 50 degrees C, at a concentration of SsEF-1 beta 5-fold higher than that of SsEF-1 alpha x [3H]GDP the rate of the exchange of [3H]GDP for GTP becomes about 160-fold faster. An analysis of the values of the energetic parameters indicates that in the presence of SsEF-1 beta the GDP/GTP exchange is entropically favoured. At 100 degrees C the half-life of SsEF-1 beta is about 4 h.

Purification and characterization of a trypanothione-glutathione thioltransferase from Trypanosoma cruzi

Although trypanothione [T(S)2] is the major thiol component in trypanosomatidae, significant amounts of glutathione are present in Trypanosoma cruzi. This could be explained by the existence of enzymes using glutathione or both glutathione and T(S)2 as cofactors. To assess these hypotheses, a cytosolic fraction of T. cruzi epimastigotes was subjected to affinity chromatography columns using as ligands either S-hexylglutathione or a non-reducible analogue of trypanothione disulphide. A similar protein of 52 kDa was eluted in both cases. Its partial amino acid sequence indicated that it was identical with the protein encoded by the TcAc2 cDNA previously described [Schoneck, Plumas-Marty, Taibi et al. (1994) Biol. Cell 80, 1-10]. This protein showed no significant glutathione transferase activity but surprisingly catalysed the thiol-disulphide exchange between dihydrotrypanothione and glutathione disulphide. The kinetic parameters were in the same range as those determined for trypanothione reductase toward its natural substrate. This trypanothione-glutathione thioltransferase provides a new target for a specific chemotherapy against Chagas' disease and may constitute a link between the glutathione-based metabolism of the host and the trypanothione-based metabolism of the parasite.