Trypanosoma rangeli sialidase lacks trans-sialidase activity

Recent progress on health effects and biosynthesis of two key sialylated human milk oligosaccharides, 3'-sialyllactose and 6'-sialyllactose

Human milk oligosaccharides (HMOs), the third major solid component in breast milk, are recognized as the first prebiotics for health benefits in infants. Sialylated HMOs are an important type of HMOs, accounting for approximately 13% of total HMOs. 3'-Sialyllactose (3'-SL) and 6'-sialyllactose (6'-SL) are two simplest sialylated HMOs. Both SLs display promising prebiotic effects, especially in promoting the proliferation of bifidobacteria and shaping the gut microbiota. SLs exhibit several health effects, including antiadhesive antimicrobial ability, antiviral activity, prevention of necrotizing enterocolitis, immunomodulatory activity, regulation of intestinal epithelial cell response, promotion of brain development, and cognition improvement. Both SLs have been approved as "Generally Recognized as Safe" by the American Food and Drug Administration and are commercially added to infant formula. The biosynthesis of SLs using enzymatic or microbial approaches has been widely studied. The enzymatic synthesis of SLs can be realized by two types of enzymes, sialidases with trans-sialidase activity and sialyltransferases. Microbial synthesis can be achieved by the multiple recombinant bacteria in one-pot reaction, which express the enzymes involved in SL synthesis pathways separately or in combination, or by metabolically engineered strains in a fermentation process. In this article, the physiological properties of 3'-SL and 6'-SL are summarized in detail and the biosynthesis of these SLs via enzymatic and microbial synthesis is comprehensively reviewed.

Unraveling the differences of the hydrolytic activity of Trypanosoma cruzi trans-sialidase and Trypanosoma rangeli sialidase: a quantum mechanics-molecular mechanics modeling study

Chagas' disease, also known as American trypanosomiasis, is a lethal, chronic disease that currently affects more than 10 million people in Central and South America. The trans-sialidase from Trypanosoma cruzi (T. cruzi, TcTS) is a crucial enzyme for the survival of this parasite: sialic acids from the host are transferred to the cell surface glycoproteins of the trypanosome, thereby evading the host's immune system. On the other hand, the sialidase of T. rangeli (TrSA), which shares 70% sequence identity with TcTS, is a strict hydrolase and shows no trans-sialidase activity. Therefore, TcTS and TrSA represent an excellent framework to understand how different catalytic activities can be achieved with extremely similar structures. By means of combined quantum mechanics-molecular mechanics (QM/MM, SCC-DFTB/Amberff99SB) calculations and umbrella sampling simulations, we investigated the hydrolysis mechanisms of TcTS and TrSA and computed the free energy profiles of these reactions. The results, together with our previous computational investigations, are able to explain the catalytic mechanism of sialidases and describe how subtle differences in the active site make TrSA a strict hydrolase and TcTS a more efficient trans-sialidase.

Surface topology evolution of Trypanosoma trans-sialidase

The trans-sialidase (TS) from Trypanosoma cruzi is a multifunctional protein given by its enzymatic activity and binding properties. The complex structure of TS promotes topology changes over the protozoa's surface with dramatic consequences for its biology. Detailed sequence analyses show that the evolution of TS in T. cruzi and other trypanosomes as well as its genomic organization is even more complex than it has been supposed before. All of these aspects are still neglected when TS is selected as a target for drug design and chemotherapy of Chagas' disease. Herein these aspects are discussed in the context of TS multifunctionality and dynamics drug design.

Free-energy computations identify the mutations required to confer trans-sialidase activity into Trypanosoma rangeli sialidase

Trypanosoma rangeli's sialidase (TrSA) and Trypanosoma cruzi's trans-sialidase (TcTS) are members of the glycoside hydrolase family 33 (GH-33). They share 70% of sequence identity and their crystallographic Cα RMSD is 0.59 Å. Despite these similarities they catalyze different reactions. TcTS transfers sialic acid between glycoconjugates while TrSA can only cleave sialic acid from sialyl-glyconjugates. Significant effort has been invested into unraveling the differences between TrSA and TcTS, and into conferring TrSA with trans-sialidase activity through appropriate point mutations. Recently, we calculated the free-energy change for the formation of the covalent intermediate (CI) in TcTS and performed an energy decomposition analysis of that process. In this article we present a similar study for the formation of the CI in TrSA, as well as in a quintuple mutant (TrSA5mut), which has faint trans-sialidase activity. The comparison of these new results with those previously obtained for TcTS allowed identifying five extra mutations to be introduced in TrSA5mut that should create a mutant (TrSA10mut ) with high trans-sialidase activity.

The Trypanosoma rangeli trypomastigote surfaceome reveals novel proteins and targets for specific diagnosis

Sympatric distribution and sharing of hosts and antigens by Trypanosoma rangeli and Trypanosoma cruzi, the etiological agent of Chagas' disease, often incur in misdiagnosis and improper epidemiological inferences. Many secreted and surface proteins (SP) have been described as important antigens shared by these species. This work describes the T. rangeli surfaceome obtained by gel-free (LC-ESI-MS/MS) and gel-based (GeLC-ESI-MS/MS) proteomic approaches, and immunoblotting analyses and the comparison of these SP with T. cruzi. A total of 138 T. rangeli proteins and 343 T. cruzi proteins were obtained, among which, 42 and 157 proteins were exclusively identified in T. rangeli or T. cruzi trypomastigotes, respectively. Immunoblotting assays using sera from experimentally infected mice revealed a distinct band pattern for each species. MS/MS analysis of T. rangeli exclusive bands revealed two unique GP63-related proteins and flagellar calcium-binding protein. Also, a ~32kDa band composed of 12 distinct proteins was exclusively recognized by anti-T. cruzi serum. This highly sensitive proteomic assessment of surface proteins characterized the T. rangeli surfaceome, revealing several differences and similarities between these two parasites. The study reports new T. rangeli-specific proteins with promising use in differential diagnosis from T. cruzi.

BIOLOGICAL SIGNIFICANCE

In this manuscript, we report the first proteomic analysis of the T. rangeli surface (surfaceome), a non-pathogenic parasite occurring in sympatry with T. cruzi, the etiological agent of Chagas disease. This comparative proteomic analysis was performed using high-throughput in-gel and gel-free proteomic approaches combined with immunoblotting, allowing us to identify new T. rangeli-specific proteins with promising use in differential serodiagnosis, among several other protein not previously reported for this taxon. Additionally, cross-recognition assays showed that T. cruzi surface proteins were recognized by heterologous serum (anti-T. rangeli) that strengthens the possibility of misdiagnosis of Chagas disease in humans and other mammals. Thus, this work provides new insights to understand the serological cross-reactivity between T. cruzi and T. rangeli, as well as, the identification of targets for specific T. rangeli diagnosis as revealed by the comparative surfaceome analysis. We strongly believe that this research is of importance to the readers of Journal of Proteomics since it provides new potential markers for diagnosis of both T. cruzi and T. rangeli parasites increasing the spectrum of specific targets for unambiguous diagnosis of T. rangeli and T. cruzi infections, besides describing new approaches to assess the trypanosomatids proteome.

Molecular analysis of surface glycoprotein multigene family TrGP expressed on the plasma membrane of Trypanosoma rangeli epimastigotes forms

Trypanosoma rangeli, a non-pathogenic hemoflagelate that in Central and South America infects humans, shares with Trypanosoma cruzi reservoirs and triatomine vectors, as well as geographical distribution. Recently, we have described in T. rangeli a truncated gene copy belonging to the group II of the trans-sialidase superfamily (TrGP). This superfamily, collectively known in T. cruzi as gp85/TS, includes members that are involved in host cell invasion and infectivity. To confirm the presence of this superfamily in the genome of T. rangeli and obtain a better knowledge of its characteristics, we designed a PCR and RT-PCR cloning strategy to allow sequence analysis of both genomic and transcribed copies. We identified two full-length copies of TrGP, some pseudogenes, and N- and C-terminal sequences of several genes. We also analyzed the expression and cellular localization of these proteins in epimastigote forms of a Venezuelan T. rangeli isolate using polyclonal antibodies made against a recombinant peptide from the N-terminal region of a TrGP member. We confirmed that TrGP is a multigenic family that shares many features with T. cruzi gp85/TS, including the telomeric location of some of its members, and by immunofluorescence analysis that its location is at the surface of the parasite.

Modulation of catalytic function by differential plasticity of the active site: case study of Trypanosoma cruzi trans-sialidase and Trypanosoma rangeli sialidase

trans-Sialidase is an essential enzyme for Trypanosoma cruzi, the causative agent of Chagas' disease, to escape from the host immune system and to invade the host cells. Therefore, T. cruzi trans-sialidase (TcTS) presents a potential and appealing therapeutic target for this lethal disease. The availability of a structurally very similar enzyme with strict hydrolase activity (Trypanosoma rangeli sialidase, TrSA) provides us a unique opportunity to understand the determinants of their structure and catalytic mechanism. In this study, we compare the catalytic cleft plasticity of free (apo) and ligand-bound (holo) forms of the two enzymes using molecular dynamics simulations. We focus on the mouth of the catalytic cleft that is defined by two residues: W312 and Y119 in TcTS and W312 and S119 in TrSA. Our results indicate that TcTS has a very flexible, widely open catalytic cleft, mostly due to W312 loop motion, in apo form. However, when the catalytic cleft is occupied by a ligand, the flexibility and solvent exposure of TcTS is significantly reduced. On the other hand, TrSA maintains a more open catalytic cleft compared to its crystal structures in both apo and holo forms (and compared to TcTS in holo forms). The reduced solvent exposure of TcTS catalytic cleft might be partially or fully responsible for TcTS to be a less efficient hydrolase than TrSA.

A sialidase mutant displaying trans-sialidase activity

Trypanosoma cruzi, the agent of Chagas disease, expresses a modified sialidase, the trans-sialidase, which transfers sialic acid from host glycoconjugates to beta-galactose present in parasite mucins. Another American trypanosome, Trypanosoma rangeli, expresses a homologous protein that has sialidase activity but is devoid of transglycosidase activity. Based on the recently determined structures of T.rangeli sialidase (TrSA) and T.cruzi trans-sialidase (TcTS), we have now constructed mutants of TrSA with the aim of studying the relevant residues in transfer activity. Five mutations, Met96-Val, Ala98-Pro, Ser120-Tyr, Gly249-Tyr and Gln284-Pro, were enough to obtain a sialidase mutant (TrSA(5mut)) with trans-sialidase activity; and a sixth mutation increased the activity to about 10% that of wild-type TcTS. The crystal structure of TrSA(5mut) revealed the formation of a trans-sialidase-like binding site for the acceptor galactose, primarily defined by the phenol group of Tyr120 and the indole ring of Trp313, which adopts a new conformation, similar to that in TcTS, induced by the Gln284-Pro mutation. The transition state analogue 2,3-didehydro-2-deoxy-N-acetylneuraminic acid (DANA), which inhibits sialidases but is a poor inhibitor of trans-sialidase, was used to probe the active site conformation of mutant enzymes. The results show that the presence of a sugar acceptor binding-site, the fine-tuning of protein-substrate interactions and the flexibility of crucial active site residues are all important to achieve transglycosidase activity from the TrSA sialidase scaffold.

The high resolution structures of free and inhibitor-bound Trypanosoma rangeli sialidase and its comparison with T. cruzi trans-sialidase

The structure of the recombinant Trypanosoma rangeli sialidase (TrSA) has been determined at 1.6A resolution, and the structures of its complexes with the transition state analog inhibitor 2-deoxy-2,3-dehydro-N-acetyl-neuraminic acid (DANA), Neu-5-Ac-thio-alpha(2,3)-galactoside (NATG) and N-acetylneuraminic acid (NANA) have been determined at 1.64A, 2.1A and 2.85A, respectively. The 3D structure of TrSA is essentially identical to that of the natural enzyme, except for the absence of covalently attached sugar at five distinct N-glycosylation sites. The protein exhibits a topologically rigid active site architecture that is unaffected by ligand binding. The overall binding of DANA to the active site cleft is similar to that observed for other viral and bacterial sialidases, dominated by the interactions of the inhibitor carboxylate with the conserved arginine triad. However, the interactions of the other pyranoside ring substituents (hydroxyl, N-acetyl and glycerol moieties) differ between trypanosomal, bacterial and viral sialidases, providing a structural basis for specific inhibitor design. Sialic acid is found to bind the enzyme with the sugar ring in a distorted (half-chair or boat) conformation and the 2-OH hydroxyl group at hydrogen bonding distance of the carboxylate of Asp60, substantiating a direct catalytic role for this residue. A detailed comparison of TrSA with the closely related structure of T.cruzi trans-sialidase (TcTS) reveals a highly conserved catalytic center, where subtle structural differences account for strikingly different enzymatic activities and inhibition properties. The structure of TrSA in complex with NATG shows the active site cleft occupied by a smaller compound which could be identified as DANA, probably the product of a hydrolytic side reaction. Indeed, TrSA (but not TcTS) was found to cleave O and S-linked sialylated substrates, further stressing the functional differences between trypanosomal sialidases and trans-sialidases.

Antigenic significance of a Trypanosoma rangeli sialidase

The Trypanosoma rangeli-secreted sialidase was purified by bovine submaxillary gland mucin-sepharose affinity chromatography. In immunoblotting analysis, antibodies raised against this molecule recognized polypeptides of 73 kDa in T. rangeli medium supernatant (TrSialr) and of 70 kDa in the cell lysates of T. rangeli (TrSials) and T. cruzi (TcSialL) epimastigotes. TrSialr, TrSials, and TcSialL were subjected to proteolytic cleavage with papain; the resultant peptide pattern displayed differences in the immunoblotting profiles. TrSials was purified by immunoprecipitation, and this protein band was recognized by sera from T. cruzi-infected chronic mice and Chagas' disease patients. In contrast, TrSialr was not recognized by these sera. The antibodies from the infected mice also recognized a band of 70 kDa present in the medium. These preliminary observations imply that the released and somatic sialidases are partially different molecules, with probably different biological roles. The related proteins recognized in T. rangeli and T. cruzi epimastigotes share many antigenic characteristics but have some structural differences, probably related to their function in the parasitic cell. On the basis of the strong antigenicity of TrSials, this molecule is proposed as the antigen for the detection of antibodies arising during T. cruzi infection.

Trypanosoma rangeli sialidase: kinetics of release and antigenic characterization

The epimastigote stage of Trypanosoma rangeli release a sialidase with a high sialic acid hydrolysis capacity. We demonstrate that sialidase secretion is an active process that is reduced at low temperatures and in the presence of sodium azide. The enzyme is continuously released until certain maximally active concentrations are attained in the BHI culture medium when the parasite density reaches 2-3 x 10(6) cells. When introduced into culture medium already containing such enzyme levels, freshly harvested parasites do not secrete additional sialidase. These findings suggest a self-regulating mechanism and a biological role for the secreted T. rangeli sialidase. The secreted enzyme was purified to homogeneity by fractionation with ammonium sulphate and affinity chromatography. Antibodies raised against the purified molecule recognized antigens of similar molecular weights (73 kDa) in western immunoblotting analyses of T. rangeli and T. cruzi whole cell lysates. No antigenic recognition was recorded against T. cruzi active sialidase/trans-sialidase polypeptides or Clostridium perfringens and Vibrio cholerae commercial sialidases. These observations may indicate the expression of different antigenic domains in T. rangeli, T. cruzi and bacterial sialidases.

Isolation and expression of an open reading frame encoding sialidase from Trypanosoma rangeli

Several protozoan parasites of human have been found to express enzymes capable of releasing terminal sialic acid residues from host glycans. These include enzymes similar in activity to bacterial and viral sialidases, as well as a novel type of enzyme, trans-sialidase, which can transfer sialic acid from one carbohydrate chain to another. Here we report the isolation of a gene and a gene fragment from the kinetoplastid Trypanosoma rangeli which encode products related in sequence to the trans-sialidase enzyme of T. cruzi. The gene fragment ORF is nearly identical to that of the complete gene, which encodes an enzymatically inactive protein. When the ORF of the gene fragment is fused to fragments from related genes, it encodes a product with sialidase activity. Both predicted T. rangeli protein products also have other potential structural features found in bacterial sialidases and in members of a previously described Trypanosoma trans-sialidase superfamily.

Immunoparasitological studies of Trypanosoma cruzi low virulence clones from Panama: humoral immune responses and antigenic cross-reactions with Trypanosoma rangeli in experimentally infected mice

The kinetics of humoral immune responses were investigated in mice experimentally infected with five clones of Trypanosoma cruzi isolated from different sources in Panama. Sera were collected at different timepoints post-infection. ELISA and IHA tests were used to detect antibodies against T. cruzi epimastigote antigens. The levels of T. cruzi specific antibodies increased during the course of infection; at day 90 post-infection the range was between 1:5120 and 1:10240. A high correlation was evident between ELISA and IHA results. Western blots revealed that these antibodies recognized polypeptides of 81, 76 and 71 KDa during the first weeks and 81, 76, 71, 50, 40, 28 and 12 KDa after 30-50 days. Only minor differences in antigen recognition patterns were demonstrated, suggesting that the major antigens may be represented in all clones. T. rangeli antigens were also recognized by T. cruzi seropositive sera. However, an ELISA test using antigens isolated from a genomic expression library of T. cruzi revealed that a hyperimmune rabbit serum against T. rangeli was unable to recognize the repeat sequence of SAPA (Shed Acute Phase Antigen) peptides but did recognize a number of other T. cruzi synthetic peptide antigens. The importance of these findings, in the context of Chagas' disease, is discussed.

Trans-sialidase and sialidase activities discriminate between morphologically indistinguishable trypanosomatids

The expression of trans-sialidase and sialidase activities in the kinetoplastid protozoa was explored as a potential marker to discriminate between the morphologically indistinguishable flagellates isolated from human, insects and vertebrate reservoir hosts. By virtue of the differences observed in the ratios of these enzyme activities, a collection of 52 species and strains comprising the major taxa of these parasites could be separated into four expression types. Type-I parasites express comparable levels of both trans-sialidase and sialidase activities (Endotrypanum species and Trypanosoma lewisi). Type-II parasites express predominantly trans-sialidase activity (Trypanosoma cruzi and Trypanosoma conorhini). Type-III parasites express sialidase activity exclusively (Trypanosoma rangeli and Trypanosoma leeuwenhoeki). Type-IV parasites do not express either activity (Leishmania species and Trypanoplasma borreli). The measurement of trans-sialidase and sialidase activities thus permits the differentiation of parasites frequently found in the same insect vectors that are difficult to distinguish, such as T. cruzi and T. rangeli, or in the same sylvatic vertebrate and invertebrate hosts, such as Leishmania and Endotrypanum.

Combined occurrence of trypanosomal sialidase/trans-sialidase activities and leishmanial metalloproteinase gene homologues in Endotrypanum sp

Endotrypanum (order Kinetoplastida: family Trypanosomatidae) is a parasite of forest dwelling tree sloths (Edentata: genera Choleopus and Bradypus). Unique among the haemoflagellates, this protozoan has an intraerythrocytic phase in the mammalian host. Nevertheless, many striking similarities exist between Endotrypanum and the human pathogen Leishmania that make it a useful model for epidemiological and evolutionary aspects of the biology of trypanosomatids. Importantly, Endotrypanum species share both the insect vector and host reservoir with certain species of Leishmania (subgenus Viannia). Because mixed infections with Endotrypanum and Leishmania are common in sloths and, therefore, likely to occur in the sandfly vector, there is a need for adequate biochemical markers to distinguish Endotrypanum from Leishmania infections. In this paper we show that Endotrypanum promastigotes possess sialidase and trans-sialidase activities, which are absent from Leishmania, and which are not closely related to the previously described trypanosomal sialidase/trans-sialidase enzyme. We also document the occurrence in Endotrypanum of homologues of the leishmanial surface metalloproteinase gp63 genes. The combined occurrence of sialidase/trans-sialidase activities and gp63 gene homologues in a unique organism has important ramifications for both field and laboratory studies on the biology of trypanosomatids, especially those related to host infection and evolution.