High diversity in mucin genes and mucin molecules in Trypanosoma cruzi

Mucins are highly O-glycosylated molecules which in mammalian cells accomplish essential functions, like cytoprotection and cell-cell interactions. In the protozoan parasite Trypanosoma cruzi, mucin-related glycoproteins have been shown to play a relevant role in the interaction with and invasion of host cells. We have previously reported a family of mucin-like genes in T. cruzi whose overall structure resembled that of mammalian mucin genes. We have now analyzed the relationship between these genes and mucin proteins. A monoclonal antibody specific for a mucin sugar epitope and a polyclonal serum directed to peptide epitopes in a MUC gene-encoded recombinant protein, detected identical bands in three out of seven strains of T. cruzi. Immunoprecipitation experiments confirmed these results. When expressed in eukaryotic cells, the MUC gene product is post-translationally modified, most likely, through extensive O-glycosylation. Gene sequencing showed that the central domains encoding the repeated sequences with the consensus T8KP2, varies in number from 1 to 10, and the number of Thr residues in each repeat could be 7, 8, or 10. A run of 16 to 18 Thr residues was present in some, but not all, MUC gene-derived sequences. Direct compositional analysis of mucin core proteins showed that Thr residues are much more frequent than Ser residues. The same fact occurs in MUC gene-derived protein sequences. Molecular mass determinations of the 35-kDa glycoproteins further extend the heterogeneity of the family to the natural mucin molecules. Difficulties in assigning each of the several MUC genes identified to a mucin product arise from the high diversity and partial sequence conservation of the members of this family.

A putative pyruvate dehydrogenase alpha subunit gene from Trypanosoma cruzi

A full-length DNA clone encoding a putative pyruvate dehydrogenase alpha subunit (E1 alpha) gene was isolated from a Trypanosoma cruzi (RA strain) DNA library. Sequencing of this clone revealed it to encode a 378 amino acid protein (M(r) 42774) with high sequence similarity to E1 alpha obtained from different sources. The highest score is obtained with human E1 alpha: 43,3% similarity. Southern blot analysis is consistent with the existence of a single copy of this putative T. cruzi E1 alpha gene per haploid genome in different parasite strains. Expression of this gene was demonstrated by Northern blot analysis and its trans-splicing acceptor site was identified by Polymerase Chain Reaction-mediated amplification of its cDNA.

Mapping the Trypanosoma cruzi genome: analyses of representative cosmid libraries

In order to generate contiguous cosmid coverage of the genome of the protozoan parasite Trypanosoma cruzi for large-scale sequence analysis, a cosmid library of 36864 individual, primary clones was generated. Total genomic DNA of the reference strain CL Brener was fragmented both by partial digestion with MboI and by physical shearing. For cloning, a modified cosmid vector was used that simplifies analyses such as restriction mapping. The library's representation is about 25 genome equivalents, assuming a size of 55 Mb per haploid genome. No chimerism of inserts in the clones could be detected. The colinearity between cosmid inserts and genomic DNA was verified. Also, hybridizations to the gel-separated karyotype of the organism were carried out as a quality check. Gridded onto two nylon filters, the library was analyzed with a variety of probes. Apart from being used for combined physical and transcriptional mapping of the genome, library filters and clones are also available to interested parties.

Medium scale production and purification to homogeneity of a recombinant trans-sialidase from Trypanosoma cruzi

Trypanosoma cruzi, the agent of Chagas' disease, presents an enzyme that catalyzes the transfer of sialic acid among glycoproteins and glycolipids known as trans-sialidase (TS), displaying some interesting features: 1) It differs from all other eucaryotic sialyltransferases, both kinetically and in substrate specificity and 2) it is involved in the parasite's mechanism of mammalian host cell invasion. We report here the production and purification to homogeneity of an enzymatically active recombinant TS (rTS) lacking the C-terminal amino acid repeats, using iminodiacetic metal affinity chromatography. Initial ratios of non-fusion recombinant versus total protein were very low in several expression systems tested, mainly due to high degradation rate. However, after purifying 1,330 times, we were able to obtain an essentially homogeneous preparation of rTS with a final yield of 29%. After minor changes, a modified protocol for a medium scale production was designed obtaining 0.5 mg of homogeneous rTS per liter of bacterial culture. The purified rTS behaved as a homogeneous protein in silver-stained denaturing gels, isoelectrofocusing and N-terminal sequencing having identical pH and temperature optima as the natural enzyme. Conditions to keep the rTS for long periods without a significant loss of activity were identified.

Effect of primary structure modifications in Trypanosoma cruzi neuraminidase/trans-sialidase activities

Neuraminidases have been implicated in various processes involving the interaction of pathogens and their receptor cells. Trypanosoma cruzi, the agent of Chagas disease, has an unusual neuraminidase, able to transfer bound alpha(2-3)sialic acid to a suitable acceptor rather than to water: the trans-sialidase (TcTS). This enzyme is encoded by a family of several homologous genes, some of them rendering inactive the products. We have shown that enzymatically active proteins have Tyr in position 342, whereas inactive TcTS contain a His342. We have now mutated this Tyr residue to Phe or Thr. Both mutant proteins resulted in enzymatically inactive products. Chimeras expressing parts of Salmonella typhimurium neuraminidase (NANH) and TcTS were constructed. Only the construct containing the complete NANH molecule fused to the last 272 residues of TcTS had neuraminidase activity. However this construct did not present TcTS activity. This finding suggests that other residues present in the homology region are required for TcTS activity.

The protozoan Trypanosoma cruzi has a family of genes resembling the mucin genes of mammalian cells

Mucins are heavily O-glycosylated Thr/Ser/Pro-rich molecules. Given their relevant functions, mucins and their genes have been mainly studied in higher eukaryotes. In the protozoan parasite Trypanosoma cruzi, mucin-like glycoproteins were shown to play an important role in the interaction with the surface of the mammalian cell during the invasion process. We show now that this parasite has a family of putative mucin genes, whose organization resembles the one present in mammalian cells. Different parasite isolates have different sets of genes, as defined by their central domain. Central domains, rich in codons for Thr and/or Ser and Pro residues, are made up of either a variable number of repeat units in tandem or non-repetitive sequences. Conversely, 5'- and 3'-ends from different genes in different isolates have similar sequences, suggesting their common origin. Comparison of deduced amino acid sequences revealed that all members of the family have the same putative signal peptide on the N terminus and a putative sequence for glycophosphatidylinositol anchoring on the C terminus. The deduced molecular mass of the core proteins is small (from 17 to 21 kDa), in agreement with the 1-kilobase size of the mRNA detected. Putative mucin genes in T. cruzi are located on large chromosomal bands of about 1.6-2.2 megabase pairs.

A single tyrosine differentiates active and inactive Trypanosoma cruzi trans-sialidases

Several genes encode members of the Trypanosoma cruzi (Tc) trans-sialidase (TS) family. These proteins contain an enzymatic domain on the N terminus, the only one required for TS activity, and an antigenic domain (SAPA (shed acute phase antigen) amino acid (aa) repeats) on the C terminus. Only some members of this glycoprotein family are enzymatically active. The complete sequence of two clones encoding the enzymatic domain of active and inactive protein from each of two Tc strains has now been obtained. Comparison of these sequences showed a limited divergence among them: 20 out of the 642 deduced aa in the enzymatic domain were found to differ. From these 20 aa, only one was found to be essential for enzymatic activity. A Tyr342 residue is deduced in both active proteins while a His342 is present in both inactive ones. This naturally occurring Tyr342-->His substitution completely abolished the TS activity. In addition to Tyr342, a second deduced aa, Pro231, was found to be necessary for full enzymatic TS activity; a Pro231-->Ala change rendered the TS protein partially active. Fourteen aa residues, including Tyr342, out of the 16 aa in the active site of a sialidase from Salmonella typhimurium are present at the same or very similar positions in the Tc TS.

Chromosome specific markers reveal conserved linkage groups in spite of extensive chromosomal size variation in Trypanosoma cruzi

The karyotypes of three cloned stocks, CL Brener (CL), CA I/72 (CA) and Sylvio X10/7 (X10), of Trypanosoma cruzi were studied by pulsed-field gel electrophoresis followed by ethidium bromide staining and hybridization with 35 different probes, 30 of which identified single chromosomes. The chromosome-specific probes identified between 26 and 31 chromosomal bands in the three cloned stocks, corresponding to 20 unique chromosomes in CL and 19 in CA and X10. Considering the DNA content of the parasite, it was predicted that the markers recognise at least half of all T. cruzi chromosomes. A majority of identified chromosomes showed large differences in size among different strains, in some cases by up to 50%. Interestingly, CL had in general larger chromosomes than the two other studied cloned stocks. Several of the markers showed linkage and nine different linkage groups were identified, each comprising 2-4 markers. The linkage between the markers was maintained in 8 of the 9 linkage groups when a panel comprising 26 different T. cruzi strains representing major T. cruzi populations was tested. One linkage group was found to be maintained in some strains but not in others. This result shows that chromosomal rearrangements occur in the T. cruzi genome, albeit with a low frequency. Repetitive DNA, both non-coding and in one case coding, was more abundant in the cloned stock CL Brener than in CA and X10. The information presented will make it possible to select chromosomes for the construction of physical chromosomal maps required for the T. cruzi genome project.

Trypanosoma cruzi exoantigen is a member of a 160 kDa gene family

During the chronic stage of Chagas disease a 160 kDa antigen appears in the blood of patients and remains detectable many years after the onset of the disease. This antigen is secreted by the trypomastigote form of the parasite while it is undetectable in the epimastigote form. We report here that the chronic 160 kDa exoantigen is encoded by a gene family (CEA 160 family). We describe the cloning and partial nucleotide sequence of a gene (CEA 160-1) belonging to the CEA160 family. Comparison of the gene sequence with other sequences present in the databases revealed homologies with several Trypanosoma cruzi surface antigens. Highest amino acid identity (59%) was with members of a family containing epitopes that mimic nervous tissues (Van Voorhis et al. 1993). Another related group (18-22% amino acid identity) comprises proteins of 85 or 160 kDa sharing an amino acid motif that is conserved among bacterial neuraminidases (Fouts et al. 1991; Pollevick et al. 1991; Kahn et al. 1991; Takle & Cross, 1991; Franco et al. 1993). The amino acid identities with the different antigens were not homogeneously distributed. Regions of higher identity (40-60%) were grouped in the central region of each protein.

Antibodies inhibiting Trypanosoma cruzi trans-sialidase activity in sera from human infections

Trans-sialidase, an enzyme that transfers sialic acid among macromolecules, has been implicated in invasion of host cells by Trypanosoma cruzi, the agent of Chagas' disease. Most antibodies produced in natural and experimental infections are directed to the highly antigenic C-terminal domain (shed acute-phase antigen). These antibodies do not inhibit the trans-sialidase activity, which is present in the N-terminal domain of the molecule. Antibodies able to inhibit trans-sialidase in sera from human infections have been found. TIA (trans-sialidase inhibition assay) was positive in sera from patients with acute and chronic infections. Healthy and congenitally infected infants born to mothers with Chagas' disease were also TIA-positive, but the antibody titers diminished within months after birth or after treatment. Thus, antibodies neutralizing trans-sialidase are detectable in most forms of T. cruzi human infections, and TIA may be useful in the diagnosis of Chagas' disease.

Immunoassay with recombinant Trypanosoma cruzi antigens potentially useful for screening donated blood and diagnosing Chagas disease

A new enzyme immunoassay (EIA), the Dia Kit Bio-Chagas assay (Gador S.A.), is potentially useful for detecting antibodies to Trypanosoma cruzi in the diagnosis of infected individuals and the screening of blood in blood banks. The EIA is carried out on test strips of plastic backing covered with a nitrocellulose membrane to which a mixture of recombinant T. cruzi antigens 1, 2, shed acute-phase antigen, 13, and 30 has been applied as a horizontal line. A horizontal line of human IgG is included to monitor the test procedure. The test strips exhibited homogeneity in the adsorption of the mixture of recombinant antigens (CV = 6.0%) and the human IgG (CV = 8.6%). The EIA results obtained with sera positive by xenodiagnosis showed 100% agreement between both types of tests; tested against sera with positive and negative matched results of indirect hemagglutination, immunofluorescence, and ELISA, the EIA results agreed for 99.1% (347 of 350) and 99.6% (299 of 300) of the samples, respectively.

Immunoassay with recombinant Trypanosoma cruzi antigens potentially useful for screening donated blood and diagnosing Chagas disease

A new enzyme immunoassay (EIA), the Dia Kit Bio-Chagas assay (Gador S.A.), is potentially useful for detecting antibodies to Trypanosoma cruzi in the diagnosis of infected individuals and the screening of blood in blood banks. The EIA is carried out on test strips of plastic backing covered with a nitrocellulose membrane to which a mixture of recombinant T. cruzi antigens 1, 2, shed acute-phase antigen, 13, and 30 has been applied as a horizontal line. A horizontal line of human IgG is included to monitor the test procedure. The test strips exhibited homogeneity in the adsorption of the mixture of recombinant antigens (CV = 6.0%) and the human IgG (CV = 8.6%). The EIA results obtained with sera positive by xenodiagnosis showed 100% agreement between both types of tests; tested against sera with positive and negative matched results of indirect hemagglutination, immunofluorescence, and ELISA, the EIA results agreed for 99.1% (347 of 350) and 99.6% (299 of 300) of the samples, respectively.

Mice infected with Trypanosoma cruzi produce antibodies against the enzymatic domain of trans-sialidase that inhibit its activity

trans-Sialidase (TS) is an enzymatic activity described only for trypanosomes that is involved in the invasion of host cells by Trypanosoma cruzi. The enzyme that is shed by the parasite is made of two domains, the C-terminal region containing immunodominant amino acid repeats that define the SAPA antigen and the N-terminal domain that contains the putative region for enzymatic activity. The SAPA antigen induces a strong humoral response detected shortly after infection, both in humans and in mice. This response is directed to the immunodominant domain but is irrelevant in terms of neutralization of TS activity. We now show that TS activity can be detected in sera from acutely infected mice. However, mice infected with a T. cruzi strain whose growth can be controlled by the host did not have detectable levels of TS activity in sera. In fact, sera from these mice were able to abolish TS activity. This inhibition was due to the presence of specific antibodies directed against the enzymatic domain of the protein since they also abolish the activity of a recombinant molecule lacking the immunodominant amino acid repeats. The neutralizing antibodies were present from day 30 after the infection, while antibodies to the immunodominant repeats were detected by day 8 postinoculation, suggesting that the in vivo role of these repeats is to defect the humoral response to the repeat domain until the infection is established.

Direct detection of Vibrio cholerae in stool samples

A direct method to detect Vibrio cholerae in stool samples was developed by using a PCR procedure that did not require a DNA purification step. Dilution (1/100) of stool samples prevented inhibition of the reaction by contaminants, and two consecutive PCRs, the second one with a nested primer, achieved the desired sensitivity. Comparison of the results obtained from stool swab samples processed by the two-step PCR and by an enzyme-linked immunosorbent assay using GM1 as the capture molecule showed that the former is more sensitive and gave positive results even when V. cholerae was not culturable or dead.

An unusually small gene encoding a putative mucin-like glycoprotein in Trypanosoma cruzi

The gene encoding a putative core protein of a mucin-like glycoprotein was identified in Trypanosoma cruzi. It contains five repeats of eleven amino acids each, eight of which are Thr and two of which are Pro residues. These Thr-Pro-rich repeats resemble the ones in the human MUC2 gene encoding mucin.

Trans-sialidase, SAPA amino acid repeats and the relationship between Trypanosoma cruzi and the mammalian host

During invasion of multicellular organisms, protozoan parasites expose functional molecules that become targets for the host immune response. Recent research on Trypanosoma cruzi, the agent of Chagas' disease, suggests a new model of how the parasite might deal with this problem. Several antigens of T. cruzi have tandemly repeated amino acid motifs in molecules with as yet unknown functions. In two cases, these repeats are in molecules with a defined structure or function. Both proteins are implicated in the invasion of host-cells by the parasite. One of these is the core protein of a putative mucin-like glycoprotein that has Thr/Pro-rich repeats which, by themselves, might define the structure of a highly O-glycosylated molecule. The other protein is SAPA/trans-sialidase/neuraminidase, a molecule able to transfer sialic acid, that has so far only been described in trypanosomes. The amino acid repeats present in SAPA/transsialidase/neuraminidase are unrelated to the enzymic activity and constitute an immunodominant C-terminal domain. The N-terminal domain of SAPA/trans-sialidase/neuraminidase controls the enzymic activity since a recombinant molecule lacking the repeats conserves trans-sialidase activity. That both domains are functionally independent is also indicated by experiments that show that antibodies directed against the amino acid repeats are unable to inhibit trans-sialidase activity. A large number of proteins having trans-sialidase related sequences but lacking enzymic activity are also present in the surface membrane of the parasite. The immunodominant SAPA/trans-sialidase/neuraminidase repeats, together with the complex network of cross-reacting epitopes present in related but enzymatically inactive proteins might contribute to the delay in mounting an effective antibody response.(ABSTRACT TRUNCATED AT 250 WORDS)

The action of Trypanosoma cruzi trans-sialidase on glycolipids and glycoproteins

Addition of sialic acid residues in the human pathogen Trypanosoma cruzi glycoconjugates is mediated by a trans-sialidase and not by a CMP-sialic acid:glycoconjugate sialyltransferase. Incubation of trans-sialidase with N-[galactose-14C]acetyllactosamine and O-linked oligosaccharides, N-linked glycopeptides (both obtained from fetuin) or sialyllactose showed that the last three compounds were donors of sialic acid residues to the first one. Moreover, N- and O-linked oligosaccharides in asialofetuin and asialomucin, respectively, served as acceptors of sialic acid units. Gangliosides GM3, GD1a and GT1b but not GM2, GM1a nor GD1b donated sialic acid units to N-acetyllactos amine when incubated with trans-sialidase. This showed that only sialic acid units bound to terminal galactosyl residues were transferred. GM1a was converted to GD1a, and GD1b to GT1b when incubated with the appropriate donor. The fact that asialo-GM1a was converted to a ganglioside migrating as GD1a on thin-layer chromatography suggested that sialic acid units may be transferred to internal galactosyl residues, although once linked to those residues they can not be further transferred to other glycoconjugates. Sialic acid residues linked alpha 2,3- but not alpha 2,6- or alpha 2,8- were transferred by the trans-sialidase. Methyl beta-galactoside but not methyl alpha-galactoside served as acceptor of sialic acid units, thus suggesting that terminal alpha-linked galactosyl units in T. cruzi and mammalian glycoproteins are not sialylated by the enzyme. As the trans-sialidase employed in these experiments has been shown to be located on the external surface of the parasite and to be shed to the medium, the relatively broad specificity shown by the enzyme with respect to protein- and lipid-linked oligosaccharides strongly suggests that infection by T. cruzi might alter the sialic acid distribution in glycoproteins and glycolipids of the mammalian host.

The reactivity of sera from chagasic patients against different fragments of cruzipain, the major cysteine proteinase from Trypanosoma cruzi, suggests the presence of defined antigenic and catalytic domains

Three fragments of cruzipain, expressed separately in bacterial vectors, were used to detect antibodies in sera from patients with chronic Chagas' disease. Most antibodies directed against the enzyme were found to react with the C-terminal extension, thus suggesting the presence of immunodominant B-cell epitopes within this protein domain. Immunoprecipitation with these antibodies did not impair enzyme activity. It is suggested that cruzipain consists of an enzymatic domain and a non-enzymatic, immunodominant domain, which corresponds to the C-terminal extension.

Identification of toxigenic Vibrio cholerae from the Argentine outbreak by PCR for ctx A1 and ctx A2-B

A polymerase chain reaction (PCR) to detect a region of the A1 cholera toxin gene was applied to the identification of 43 Vibrio cholerae strains isolated from the recent outbreak in Argentina. A good correlation was observed between the GM1-enzyme-linked immunosorbent assay (GM1-ELISA) to detect the B subunit of the enterotoxin and PCR. However, a V. cholerae non-01 strain that was negative by the ELISA test, was positive by the PCR assay for the A1 region. A second PCR test to detect the A2-B coding region was developed to solve this case. We propose that routine detection of toxigenic V. cholerae by PCR should include analysis of A2-B coding region or the whole cholera toxin operon.

SAPA/trans-sialidase and cruzipain: two antigens from Trypanosoma cruzi contain immunodominant but enzymatically inactive domains

Trypanosoma cruzi, the parasitic protozoan that causes the American trypanosomiasis, or Chagas disease, contains a number of antigenic molecules, some of which have tandems of amino acid repeats. One of these molecules, SAPA (shed acute phase antigen), contains a so-far unique trans-sialidase activity that is essential for penetration of the parasite into mammalian cells. The enzyme consists of two different domains, one presumably enzymatic, which contains four copies of an amino acid motif conserved in bacterial neuraminidases, and the other highly antigenic, consisting of the repeats. Another enzyme that seems to be involved in the host-parasite relationship, the cysteine proteinase cruzipain, is also made up in its mature form of a catalytic domain with high homology to cathepsin L and a COOH-terminal domain that is highly antigenic in vivo. These bifunctional molecules may have arisen by incorporation of a highly antigenic domain to an essential enzyme in order to attract the immune response, thus protecting the enzyme activity.