Nucleotide sequence of a Trypanosoma cruzi cDNA encoding a protein homologous to mammalian EF1 gamma

Kinetics and diagnostic and prognostic potential of quantitative Western blot analysis and antigen-specific enzyme-linked immunosorbent assay in experimental canine leishmaniasis

Quantitative computerized Western blot analysis of antibody responses during experimental canine Leishmania infantum infection distinguished between immunodominant and nonimmunodominant protein bands. Six infected beagles, positive by both PCR and parasite culture, were monitored over 75 weeks postinfection and during a 12-week allopurinol treatment course. All dogs were symptomatic at the time of treatment. Of 12 antigenic bands examined, the immunodominant bands (12, 14, 24, 29, 48, and 68 kDa) showed significantly increased intensities (P<0.01) and higher frequencies of recognition than the nonimmunodominant bands at all time points. Detection of the former bands at 6 weeks postinfection preceded seroconversion by enzyme-linked immunosorbent assay (ELISA) both on crude Leishmania antigen or the recombinant proteins rK39 and HSP70. Reactivity with the 14-, 48-, and 68-kDa bands signified early infection, whereas increased reactivity with the 14-, 24-, and 29-kDa bands was associated with posttreatment parasite persistence and potential unfavorable prognosis. Total lane intensity (TLI) emerged as a sensitive marker for early infection and increased as early as 4 weeks postinfection. TLI had a significantly higher (P<0.01) relative increase rate than crude Leishmania antigen or HSP70 or rK39 ELISA at all time points. These immunodominant antigens and TLI, as determined by quantitative Western blotting, will be valuable for early detection and treatment evaluation of canine leishmaniasis.

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.

Isolation and characterization of Leishmania infantum cDNA encoding a protein homologous to eukaryotic elongation factor 1 gamma

This paper reports the isolation and characterization of a complementary deoxyribonucleic acid clone showing sequence homology with genes coding for the eukaryotic elongation factor 1 gamma (EF-1 gamma). The clone encodes an open reading frame of 404 amino acids corresponding to a deduced molecular mass of 46.2 kDa. Database searches revealed 30-64% sequence identity between the Leishmania infantum EF-1 gamma and several eukaryotic homologues. Southern blot analysis indicated that 2 genes tandemly organized were present in the L. infantum genome. The 3' untranslated regions of these 2 genes differed in size. Southern hybridization and pulsed field gel electrophoresis showed that EF-1 gamma genes are highly conserved among members of the Leishmania genus and must be clustered in a single chromosomal locus.

Novel organization and sequences of five genes encoding all six enzymes for de novo pyrimidine biosynthesis in Trypanosoma cruzi

A 25 kb segment of genomic DNA from Trypanosoma cruzi, the causative agent of Chagas' disease, was sequenced. It contains five genes, pyr1, pyr2, pyr3, pyr4, and pyr6-5, encoding all six enzymes involved in de novo pyrimidine biosynthesis, glutamine-dependent carbamoyl-phosphate synthetase, aspartate carbamoyltransferase, dihydroorotase, dihydroorotate dehydrogenase, and orotidine-5'-phosphate decarboxylase linked with orotate phosphoribosyltransferase, respectively. The pyr genes constitute a polycistronic transcription unit on an 800 kb chromosomal DNA in the order of pyr1, pyr3, pyr6-5, pyr2, and pyr4 from the 5' terminus, with intervening sequences of 2.2, 0.4, 8.1, and 0.8 kb. The amino acid sequences deduced from the trypanosomatid pyr genes, except for pyr6, showed closer similarities to mammalian and yeast sequences, and less similarity to archaeal and bacterial sequences. The last two enzymes encoded by a single gene, pyr6-5, are covalently linked in the order opposite to mammalian pyr5-6, and possess a putative glycosomal targeting signal tripeptide, serine-lysine-leucine, at the C terminus. The calculated isoelectric points of 9.3 and 9.9 are also diagnostic of the glycosomal localization of these enzymes. We conclude that the T. cruzi pyr gene organization represents an early progenitor in de novo pyrimidine biosynthesis in eukaryotic lineage, and that the independent pyr genes may have evolved before the gene fusion events that resulted in the three mammalian-type genes, pyr1-3-2, pyr4, and pyr5-6, for UMP synthesis. Peculiarities in the trypanosomatid pyr6-5 gene product are discussed.

Isolation and characterization of a rice cDNA encoding the gamma-subunit of translation elongation factor 1B (eEF1Bgamma)

We isolated a rice cDNA clone (refg) encoding the gamma-subunit of translation elongation factor 1B (eEF-1B gamma; the old designation was EF-1 gamma). The refg encodes an open reading frame of 419 amino acids which shows a similarity to the equivalent sequences from animals and yeast. Complex formation analysis, which showed the recombinant protein of refg (His-eEF1B gamma) and formed a complex with GST-eEF-1Bbeta, indicated that the refg encodes rice eEF1B gamma of the eEF1B alphabeta gamma complex. Expression analysis showed that refg mRNA is very abundant in suspension-cultured cells during the exponential phase of growth. A DNA blot analysis indicated that refg is located at a single locus in the rice genome.

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.

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.