THE SURFACE TRANS -SIALIDASE FAMILY OF TRYPANOSOMA CRUZI

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121

Trypanosoma cruzi causing Chagas' disease needs to invade host cells to complete its life cycle. Macromolecules on host cell surfaces such as laminin, thrombospondin, heparan sulfate, and fibronectin are believed to be important in mediating parasite-host cell adhesions and in the invasion process of the host cell by the parasite. The SELEX technique (systematic evolution of ligands by exponential enrichment) was used to evolve nuclease-resistant RNA ligands (aptamer ‫؍‬ to fit) that bind with affinities of 40 -400 nM to parasite receptors for the host cell matrix molecules laminin, fibronectin, thrombospondin, and heparan sulfate. After eight consecutive rounds of in vitro selection four classes of RNA aptamers based on structural similarities were isolated and sequenced. All members of each class shared a common sequence motif and competed with the respective host cell matrix molecule that was used for displacement during the selection procedure. RNA pools following seven and eight selection rounds as well as individual aptamers sharing consensus motifs were active in inhibiting invasion of LLC-MK 2 monkey kidney cells by T. cruzi in vitro.

Section: Discussionmentioning

confidence: 99%

In Vitro Selection of RNA Aptamers That Bind to Cell Adhesion Receptors of Trypanosoma cruzi and Inhibit Cell Invasion

Ulrich¹,

Magdesian²,

Alves³

et al. 2002

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121

“…The corresponding cDNA insert has significant sequence identity with members of the gp85/trans-sialidase gene family of T. cruzi (23)(24)(25), raising the interesting hypothesis that several members of that superfamily may possess adhesive capacity to different receptor molecules either located on the cell surface or belonging to components of the extracellular matrix.…”

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confidence: 99%

Cloning of a Surface Membrane Glycoprotein Specific for the Infective Form of Trypanosoma cruzi Having Adhesive Properties to Laminin

Giordano¹,

Fouts²,

Tewari³

et al. 1999

113

Trypomastigotes ofFor the first time it was possible to assign a defined ligand to a sequenced glycoprotein belonging to the gp85 family. This fact, together with the reported binding of family members to cell surfaces, reinforces the hypothesis that this family encodes glycoproteins with similar sequences but differing enough as to bind to different ligands and thus forming a family of adhesion glycoproteins enabling the parasite to overcome the barriers interposed by cell membranes, extracellular matrices, and basal laminae.

“…Once the infected cell is full of parasites, and probably deprived of nutrients, the amastigote form transforms into nonproliferative and infective trypomastigote forms, which rupture the cell, escaping to the bloodstream. The differentiation between noninfective and infective forms is related to the shutdown of the proliferative machinery and the expression of a set of genes involved in cell invasion and induction of resistance to host defenses (14,15). These changes are correlated to the activation of adenylate cyclase (16 -21) via transducing pathways involving G-proteins (22,23), phospholipase C (20), and calcium internalization (24).…”

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confidence: 99%

“…These changes are correlated to the activation of adenylate cyclase (16 -21) via transducing pathways involving G-proteins (22,23), phospholipase C (20), and calcium internalization (24). The molecules expressed during this phase of differentiation are members of a large family of 85-kDa glycoproteins (14) that are localized on the surface of infective forms and are thought to participate in adhesion to the host cell surface during invasion (25)(26)(27). The large family of 85-kDa glycoproteins, collectively baptized as gp85 (14), encompasses a subfamily of several members, earlier defined as Tc85, that are capable of binding to wheat germ agglutinin (28) and are recognized by a specific monoclonal antibody (29).…”

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confidence: 99%

“…The molecules expressed during this phase of differentiation are members of a large family of 85-kDa glycoproteins (14) that are localized on the surface of infective forms and are thought to participate in adhesion to the host cell surface during invasion (25)(26)(27). The large family of 85-kDa glycoproteins, collectively baptized as gp85 (14), encompasses a subfamily of several members, earlier defined as Tc85, that are capable of binding to wheat germ agglutinin (28) and are recognized by a specific monoclonal antibody (29). The most acidic component of the Tc85 subfamily was characterized as a laminin ligand (30), which may be directly involved in the interaction of trypomastigotes with the mammalian cell (25,29 entiated trypomastigotes is the enzyme trans-sialidase (TS).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Expression of trans-Sialidase and 85-kDa Glycoprotein Genes in Trypanosoma cruzi Is Differentially Regulated at the Post-transcriptional Level by Labile Protein Factors

Abuin¹,

Freitas‐Junior²,

Colli³

et al. 1999

To adapt to different environments, Trypanosoma cruzi, the protozoan parasite that causes Chagas' disease, expresses a different set of proteins during development. To begin to understand the mechanism that controls this differential gene expression, we have analyzed the levels of amastin and trans-sialidase mRNAs and the mRNAs encoding members of the 85-kDa glycoprotein gene family, which are differentially expressed in the T. cruzi stages found in the mammalian host. Amastin mRNA is expressed predominantly in intracellular and proliferative amastigotes. trans-Sialidase mRNAs are found mostly in forms undergoing transformation from amastigotes to trypomastigotes inside infected cells, whereas mRNAs encoding the 85-kDa glycoproteins appear only in the infective trypomastigotes released from the cells. The genes coding for these mRNA species are constitutively transcribed in all stages of T. cruzi cells, suggesting that expression is controlled post-transcriptionally during differentiation. Inhibition of transcription by actinomycin D revealed that each mRNA species has a relatively long half-life in stages where it accumulates. In the case of the transsialidase and 85-kDa glycoprotein genes, mRNA accumulation was induced by treatment with the protein synthesis inhibitor cycloheximide at the stages that preceded the normal accumulation. Therefore, mRNA stabilization may account for mRNA accumulation. mRNA degradation could be promoted by proteins with high turnover, or stabilization could be promoted by forming a complex with the translational machinery at defined times in development. Identification of the factors that induce mRNA degradation or stabilization is essential to the understanding of control of gene expression in these organisms.Gene expression in Trypanosoma cruzi as well as in other trypanosomes is largely controlled at the post-transcriptional level (1-6), although there are a few exceptions where promoters and transcriptional activation have been described (7). Well defined RNA polymerase II initiation sites have not been found, and most genes are transcribed as part of polycistronic units and are processed by trans-splicing (8, 9). During processing, capped spliced leader sequence is added to the 5Ј-end, and a polyadenosine tail is added to the 3Ј-end of mRNA (10), probably ensuring mRNA stability and transport to the cytoplasm (11). In particular, correct splicing and polyadenylation, as well as the existence of specific 3Ј-untranslated portions of the transcribed genes, have been shown to promote either mRNA stability (12) or an increase in the translational efficiency (13). However, the nature of controlling factors and how environmental modifications induce differential expression remain obscure.T. cruzi provides an attractive model to study how modifications in the environment induce differential gene expression. In the insect host, the epimastigote form of the parasite proliferates in the gut. In the posterior gut, where the nutrients become scarce, the parasite transforms into metacyclic ...