Purification and characterization of a novel sialidase found in procyclic culture forms of Trypanosoma brucei

N-glycosylation modulates enzymatic activity of Trypanosoma congolense trans-sialidase

Trypanosomes cause the devastating disease trypanosomiasis, in which the action of trans-sialidase (TS) enzymes harbored on their surface is a key virulence factor. TS enzymes are N-glycosylated, but the biological functions of their glycans have remained elusive. In this study, we investigated the influence of N-glycans on the enzymatic activity and structural stability of TconTS1, a recombinant TS from the African parasite Trypanosoma congolense. We expressed the enzyme in Chinese hamster ovary Lec1 cells, which produce high-mannose type N-glycans similar to the TS N-glycosylation pattern in vivo. Our MALDI-TOF mass spectrometry data revealed that up to eight putative N-glycosylation sites were glycosylated. In addition, we determined that N-glycan removal via endoglycosidase H_f treatment of TconTS1 led to a decrease in substrate affinity relative to the untreated enzyme but had no impact on the conversion rate. Furthermore, we observed no changes in secondary structure elements of hypoglycosylated TconTS1 in CD experiments. Finally, our molecular dynamics simulations provided evidence for interactions between monosaccharide units of the highly flexible N-glycans and some conserved amino acids located at the catalytic site. These interactions led to conformational changes, possibly enhancing substrate accessibility and enzyme–substrate complex stability. The here-observed modulation of catalytic activity via N-glycans represents a so-far-unknown structure–function relationship potentially inherent in several members of the TS enzyme family.

Elimination of GPI2 suppresses glycosylphosphatidylinositol GlcNAc transferase activity and alters GPI glycan modification in Trypanosoma brucei

Many eukaryotic cell-surface proteins are post-translationally modified by a glycosylphosphatidylinositol (GPI) moiety that anchors them to the cell membrane. The biosynthesis of GPI anchors is initiated in the endoplasmic reticulum by transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol. This reaction is catalyzed by GPI GlcNAc transferase, a multisubunit complex comprising the catalytic subunit Gpi3/PIG-A as well as at least five other subunits, including the hydrophobic protein Gpi2, which is essential for the activity of the complex in yeast and mammals, but the function of which is not known. To investigate the role of Gpi2, we exploited Trypanosoma brucei (Tb), an early diverging eukaryote and important model organism that initially provided the first insights into GPI structure and biosynthesis. We generated insect-stage (procyclic) trypanosomes that lack TbGPI2 and found that in TbGPI2-null parasites, (i) GPI GlcNAc transferase activity is reduced, but not lost, in contrast with yeast and human cells, (ii) the GPI GlcNAc transferase complex persists, but its architecture is affected, with loss of at least the TbGPI1 subunit, and (iii) the GPI anchors of procyclins, the major surface proteins, are underglycosylated when compared with their WT counterparts, indicating the importance of TbGPI2 for reactions that occur in the Golgi apparatus. Immunofluorescence microscopy localized TbGPI2 not only to the endoplasmic reticulum but also to the Golgi apparatus, suggesting that in addition to its expected function as a subunit of the GPI GlcNAc transferase complex, TbGPI2 may have an enigmatic noncanonical role in Golgi-localized GPI anchor modification in trypanosomes.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Molecular occurrence of trypanosomes, erythrocyte and serum sialic acid concentrations of Muturu and Bunaji cattle in Benue State, Nigeria

One hundred each, of Muturu and Bunaji cattle were screened, using polymerase chain reaction (PCR), for trypanosomes in Makurdi and Gboko Local Government Areas of Benue State, Nigeria. Erythrocyte surface sialic acid (ESSA) and free serum sialic acid (FSSA) concentrations were determined and compared in both breeds with the aim of providing baseline data for research and diagnostic purposes. Five per cent (5%) and 23% of the Muturu and Bunaji cattle, respectively, were positive for trypanosomes. The result at p=0.005 was significantly different, with p value of 0.0002 and odd ratio of 0.1762. The Trypanosoma species circulating in Benue State, as detected in the two breeds of cattle, were Trypanosoma congolense, T. vivax, T. brucei and T. evansi. This study, therefore, reports for the first time a natural infection of cattle with T. evansi and the use of a novel PCR in the diagnosis of trypanosome infections in cattle in Benue State, Nigeria. The determination of the ESSA and FSSA concentrations in Muturu cattle in Nigeria is also reported for the first time. The Muturu cattle have a significantly higher ESSA than the Bunaji cattle, this may be responsible for their relative trypanotolerance.

Molecular control of irreversible bistability during trypanosome developmental commitment

Phosphoproteomic and functional analysis of the developmental progression of Trypanosomes demonstrates that this transition shows bistability, with commitment to differentiation requiring new protein synthesis, and that the protein kinase NRK is a key regulator.

The life cycle of Trypanosoma brucei involves developmental transitions that allow survival, proliferation, and transmission of these parasites. One of these, the differentiation of growth-arrested stumpy forms in the mammalian blood into insect-stage procyclic forms, can be induced synchronously in vitro with cis-aconitate. Here, we show that this transition is an irreversible bistable switch, and we map the point of commitment to differentiation after exposure to cis-aconitate. This irreversibility implies that positive feedback mechanisms operate to allow commitment (i.e., the establishment of “memory” of exposure to the differentiation signal). Using the reversible translational inhibitor cycloheximide, we show that this signal memory requires new protein synthesis. We further performed stable isotope labeling by amino acids in cell culture to analyze synchronized parasite populations, establishing the protein and phosphorylation profile of parasites pre- and postcommitment, thereby defining the “commitment proteome.” Functional interrogation of this data set identified Nek-related kinase as the first-discovered protein kinase controlling the initiation of differentiation to procyclic forms.

Genomic analyses, gene expression and antigenic profile of the trans-sialidase superfamily of Trypanosoma cruzi reveal an undetected level of complexity

The protozoan parasite Trypanosoma cruzi is the etiologic agent of Chagas disease, a highly debilitating human pathology that affects millions of people in the Americas. The sequencing of this parasite's genome reveals that trans-sialidase/trans-sialidase-like (TcS), a polymorphic protein family known to be involved in several aspects of T. cruzi biology, is the largest T. cruzi gene family, encoding more than 1,400 genes. Despite the fact that four TcS groups are well characterized and only one of the groups contains active trans-sialidases, all members of the family are annotated in the T. cruzi genome database as trans-sialidase. After performing sequence clustering analysis with all TcS complete genes, we identified four additional groups, demonstrating that the TcS family is even more heterogeneous than previously thought. Interestingly, members of distinct TcS groups show distinctive patterns of chromosome localization. Members of the TcSgroupII, which harbor proteins involved in host cell attachment/invasion, are preferentially located in subtelomeric regions, whereas members of the largest and new TcSgroupV have internal chromosomal locations. Real-time RT-PCR confirms the expression of genes derived from new groups and shows that the pattern of expression is not similar within and between groups. We also performed B-cell epitope prediction on the family and constructed a TcS specific peptide array, which was screened with sera from T. cruzi-infected mice. We demonstrated that all seven groups represented in the array are antigenic. A highly reactive peptide occurs in sixty TcS proteins including members of two new groups and may contribute to the known cross-reactivity of T. cruzi epitopes during infection. Taken together, our results contribute to a better understanding of the real complexity of the TcS family and open new avenues for investigating novel roles of this family during T. cruzi infection.

Procyclic Trypanosoma brucei expresses separate sialidase and trans-sialidase enzymes on its surface membrane

The procyclic stage of Trypanosoma brucei in the insect vector expresses a surface-bound trans-sialidase (TbTS) that transfers sialic acid from glycoconjugates in the environment to glycosylphosphatidylinositol-anchored proteins on its surface membrane. RNA interference against TbTS abolished trans-sialidase activity in procyclic cells but did not diminish sialidase activity, suggesting the presence of a separate sialidase enzyme for hydrolyzing sialic acid. A search of the T. brucei genome sequence revealed seven other putative genes encoding proteins with varying similarity to TbTS. RNA interference directed against one of these proteins, TbSA C, greatly decreased the sialidase activity but had no effect on trans-sialidase activity. The deduced amino acid sequence of TbSA C shares only 40% identity with TbTS but conserves most of the relevant residues required for catalysis. However, the sialidase has a tryptophan substitution for a tyrosine at position 170 that is crucial in binding the terminal galactose that accepts the transferred sialic acid. When this same tryptophan substitution in the sialidase was placed into the recombinant trans-sialidase, the mutant enzyme lost almost all of its trans-sialidase activity and increased its sialidase activity, further confirming that the gene and protein identified correspond to the parasite sialidase. Thus, in contrast to all other trypanosomes analyzed to date that express either a trans-sialidase or a sialidase but not both, T. brucei expresses these two enzymatic activities in two separate proteins. These results suggest that African trypanosomes could regulate the amount of critical sialic acid residues on their surface by modulating differential expression of each of these enzymes.

Characterization of a sialidase (neuraminidase) isolated fromClostridium chauvoei (Jakari strain)

A sialidase from Clostridium chauvoei (Jakari strain), an indigenous bacterial strain that causes blackleg in Nigerian cattle and other ruminants was isolated and partially purified by chromatography on DEAE cellulose, hydroxyapatite and phenyl agarose columns. The enzyme migrated as a 65-kDa protein after electrophoresis on sodium dodecyl sulphate polyacrylamide gels. It was optimally active at pH 4.5 and 40 degrees C with an activation energy (Ea) of 13.40 kJ mol(-1). It had Km and Vmax values of 170 microM and 200 micromole h(-1) mg(-1) respectively with fetuin as substrate. When sialyllactose (Neu5Ac2,3 lactose) was used as substrate the Km and Vmax values were 8 microM and 5 micromoles min(-1) mg(-1) respectively. The Clostridium chauvoei sialidase cleaved sialic acids from RBC ghosts of sheep, horse, goat, cattle, pig and mice as well as mouse brain cells, albeit at different rates. The enzyme was activated by Ca2+ and Mg2+ and inhibited by the group-specific reagents diethylpyrocarbonate (DEP) and N-ethylmalemide (NEM). The sialidase inhibitors, 2,3 didehydroneuraminic acid (Neu5Ac2,3en) and paranitrophenyl oxamic acid (pNPO) inhibited the enzyme competitively with Ki values of 40 and 30 microM respectively.

Two trans-sialidase forms with different sialic acid transfer and sialidase activities from Trypanosoma congolense

Trypanosomes express an enzyme called trans-sialidase (TS), which enables the parasites to transfer sialic acids from the environment onto trypanosomal surface molecules. Here we describe the purification and characterization of two TS forms from the African trypanosome Trypanosoma congolense. The purification of the two TS forms using a combination of anion exchange chromatography, isoelectric focusing, gel filtration, and subsequently, antibody affinity chromatography resulted, in both cases, in the isolation of a 90-kDa monomer on SDS-PAGE, which was identified as trans-sialidase using micro-sequencing. Monoclonal antibody 7/23, which bound and partially inhibited TS activity, was found in both cases to bind to a 90-kDa protein. Both TS forms possessed sialidase and transfer activity, but markedly differed in their activity ratios. The TS form with a high transfer-to-sialidase activity ratio, referred to as TS-form 1, possessed a pI of pH 4-5 and a molecular mass of 350-600 kDa. In contrast, the form with a low transfer-to-sialidase activity ratio, referred to as TS-form 2, exhibited a pI of pH 5-6.5 and a molecular mass of 130-180 kDa. Both TS forms were not significantly inhibited by known sialidase inhibitors and revealed no significant differences in donor and acceptor substrate specificities; however, TS-form 1 utilized various acceptor substrates with a higher catalytic efficiency. Interestingly, glutamic acid-alanine-rich protein, the surface glycoprotein, was co-purified with TS-form 1 suggesting an association between both proteins.

Procyclin null mutants of Trypanosoma brucei express free glycosylphosphatidylinositols on their surface

Procyclins are abundant, glycosylphosphatidylinositol (GPI)-anchored proteins on the surface of procyclic (insect) form trypanosomes. To investigate whether trypanosomes are able to survive without a procyclin coat, all four procyclin genes were deleted sequentially. Bloodstream forms of the null mutant exhibited no detectable phenotype and were able to differentiate to procyclic forms. Initially, differentiated null mutant cells were barely able to grow, but after an adaptation period of 2 mo in culture they proliferated at the same rate as wild-type trypanosomes. Analysis of these culture-adapted null mutants revealed that they were covered by free GPIs. These were closely related to the mature procyclin anchor in structure and were expressed on the surface in numbers comparable with that of procyclin in wild-type cells. However, free GPIs were smaller than the procyclin anchor, indicative of a lower number of poly-N-acetyllactosamine repeats, and a proportion contained diacylphosphatidic acid. Free GPIs are also expressed by wild-type cells, although to a lesser extent. These have been overlooked in the past because they partition in a solvent fraction (chloroform/water/methanol) that is normally discarded when GPI-anchored proteins are purified.

The trans-sialidase from the african trypanosome Trypanosoma brucei

Trypanosoma brucei is the cause of the diseases known as sleeping sickness in humans (T. brucei ssp. gambiense and ssp. rhodesiense) and ngana in domestic animals (T. brucei brucei) in Africa. Procyclic trypomastigotes, the tsetse vector stage, express a surface-bound trans-sialidase that transfers sialic acid to the glycosylphosphatidylinositol anchor of procyclin, a surface glycoprotein covering the parasite surface. Trans-sialidase is a unique enzyme expressed by a few trypanosomatids that allows them to scavenge sialic acid from sialylated compounds present in the infected host. The only enzyme extensively characterized is that of the American trypanosome T. cruzi (TcTS). In this work we identified and characterized the gene encoding the trans-sialidase from T. brucei brucei (TbTS). TbTS genes are present at a small copy number, at variance with American trypanosomes where a large gene family is present. The recombinant TbTS protein has both sialidase and trans-sialidase activity, but it is about 10 times more efficient in transferring than in hydrolysing sialic acid. Its N-terminus contains a region of 372 amino acids that is 45% identical to the catalytic domain of TcTS and contains the relevant residues required for catalysis. The enzymatic activity of mutants at key positions involved in the transfer reaction revealed that the catalytic sites of TcTS and TbTS are likely to be similar, but are not identical. As in the case of TcTS and TrSA, the substitution of a conserved tryptophanyl residue changed the substrate specificity rendering a mutant protein capable of hydrolysing both alpha-(2,3) and alpha-(2,6)-linked sialoconjugates.

Achievements and challenges of sialic acid research

Slalic acids are one of the most important molecules of life, since they occupy the terminal position on macromolecules and cell membranes and are involved in many biological and pathological phenomena. The structures of sialic acids, comprising a family of over 40 neuraminic acid derivatives, have been elucidated. However, many aspects of the regulation of their metabolism at the enzyme and gene levels, as well as of their functions remain mysterious. Sialic acids play a dual role, not only are they indispensable for the protection to and adaptation of life, but are also utilised by life-threatening infectious microorganisms. In this article the present state of knowledge in sialobiology, with an emphasis on my personal experience in this research area, is outlined including a discussion of necessary future work in this fascinating field of cell biology.

Sialic acids in fungi: a minireview

The increasing number of reports on the presence of sialic acids in fungi (N-acetyl-, N-glycolyl- and 5,9-N,O-diacetylneuraminic acids) based on direct and indirect evidence warrants the present review. Formerly suggested as sialidase-sensitive sources of anionic groups at the cell surface of fungal species grown in chemically defined media (e.g., Fonsecaea pedrosoi), sialic acids have also been found in Sporothrix schenckii, Paracoccidioides brasiliensis, Cryptococcus neoformans and recently, in Candida albicans. Methods used involved adequate hydrolysis and extraction procedures, HPTLC, gas-chromatography, colorimetry, mass spectroscopy, lectin and influenza virus binding. Apart from protecting fungal cells against phagocytosis (S. schenckii, C. neoformans) and playing a cellular structural role (F. pedrosoi), other biological functions of sialic acids are still being investigated.

The GPI-phospholipase C of Trypanosoma brucei is nonessential but influences parasitemia in mice

In the mammalian host, the cell surface of Trypanosoma brucei is protected by a variant surface glycoprotein that is anchored in the plasma membrane through covalent attachment of the COOH terminus to a glycosylphosphatidylinositol. The trypanosome also contains a phospholipase C (GPI-PLC) that cleaves this anchor and could thus potentially enable the trypanosome to shed the surface coat of VSG. Indeed, release of the surface VSG can be observed within a few minutes on lysis of trypanosomes in vitro. To investigate whether the ability to cleave the membrane anchor of the VSG is an essential function of the enzyme in vivo, a GPI-PLC null mutant trypanosome has been generated by targeted gene deletion. The mutant trypanosomes are fully viable; they can go through an entire life cycle and maintain a persistent infection in mice. Thus the GPI-PLC is not an essential activity and is not necessary for antigenic variation. However, mice infected with the mutant trypanosomes have a reduced parasitemia and survive longer than those infected with control trypanosomes. This phenotype is partially alleviated when the null mutant is modified to express low levels of GPI-PLC.

Sialidases: structures, biological significance and therapeutic potential

The structure-based design of a potent inhibitor of the influenza-virus neuraminidase (sialidase) is one of the outstanding successes of rational drug design. Recent clinical trials of the drug have stimulated many companies to seek a share of the potentially huge flu market. Sialidases, however, are involved in the pathogenesis of a whole range of other diseases, so perhaps the knowledge and expertise gained from the influenza story can be used in the design of other drugs, given that they all share certain structural features.

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.

Distribution of developmentally regulated trans-sialidases in the Kinetoplastida and characterization of a shed trans-sialidase activity from procyclic Trypanosoma congolense

The expression of developmentally regulated sialidase and trans-sialidase activities in kinetoplastid protozoa was investigated. The occurrence of these enzymes was found not to be a common feature among the Kinetoplastida, but to be restricted to distinct developmental life cycle stages of only a few species. While sialidases without trans-sialylating activities were demonstrated in Trypanosoma vivax and T. rangeli, trans-sialidase activity is expressed throughout the brucei-group and in T. congolense. Neither T. evansi, nor T. equiperdum express sialidases or trans-sialidases. Furthermore, the absence of both, sialidase and trans-sialidase activities was proven in the Leishmania, Crithidia, Herpetomonas, Leptomonas and Phytomonas, respectively. In all species tested, the occurrence of sialic acids coincides with the expression of trans-sialidase activity. Those parasites, which lack trans-sialidases or only display regular sialidases, also lack cell-bound sialic acids. The regular sialidase activity from bloodstream form T. vivax was characterized. The trans-sialidase from T. congolense is restricted to the procyclic culture forms and is shed into the culture medium. The enzyme has a pH-optimum at pH 7.0, displays sensitivity towards chlorides and is resistant against commonly used sialidase inhibitors. T. congolense trans-sialidase transfers preferentially alpha(2-3)-linked sialic acids onto terminal beta-galactose residues. Also hydroxylated sialic acids (Neu5Gc) are transferred. The major glycoprotein GARP from procyclic T. congolense was identified as one potential natural sialic acid acceptor on the parasite's surface. In order to facilitate the characterization of trans-sialidases a novel, fluorimetric trans-sialidase assay was developed.

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.

The structure, biosynthesis and function of glycosylated phosphatidylinositols in the parasitic protozoa and higher eukaryotes

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The developmentally regulated trans-sialidase from Trypanosoma brucei sialylates the procyclic acidic repetitive protein

A developmentally regulated trans-sialidase activity is present on the surface of procyclic Trypanosoma brucei. Bloodstream stages display no trans-sialidase activity. T. brucei trans-sialidase is capable of transferring sialic acids from a variety of glycoconjugates into new glycosidic linkages without requirement for CMP-Neu5Ac. The enzyme is linked to the plasma-membrane via a GPI-PLC-resistant GPI-anchor. The comparison of enzymic and structural features of sialidase and trans-sialidase suggests that the two activities may be catalyzed by the same protein, since highly enriched sialidase fractions display trans-sialidase activity. 2-Deoxy-2,3-didehydro-N-acetylneuraminic acid is only a poor inhibitor for the two enzymic activities. Sialic acids are transferred to alpha (2-3)-positions of terminal beta-galactose residues of oligosaccharides and glycoconjugates at various rates. Neu5Ac-alpha(2-3)-lactose is the best trans-sialylation donor tested. Lewis is a poor sialic acid acceptor. T. brucei trans-sialidase utilizes serum glycoconjugates, human and bovine erythrocytes as sialic acid donors, and resialylates sialidase-treated erythrocytes. The enzyme transfers sialic acids from the GPI-anchor of procyclic acidic repetitive protein (PARP) onto lactose and vice versa. Also structures within a variant surface glycoprotein (sVSG MITat. 1.7.) can be trans-sialylated.

Trypanosoma cruzi trans-sialidase and cell invasion

Trypanosoma cruzi does not synthesize sialic acid but does contain a trans-sialidase, an enzyme capable of transferring sialic acid between host glycoconjugates and the parasite. Sialic acids are negatively charged carbohydrates attached to the terminal non-reducing end of glycoproteins and glycolipids, and their presence can dramatically influence many cell-surface recognition processes. Since sialic acids have been implicated in several ligand-receptor interactions, including the interaction of pathogenic viruses, bacteria and protozoans with their hosts, the expression of trans-sialidase and the acquisition of sialic acid by T. cruzi may be relevant to the interaction of the parasite with the host, and consequently may influence the pathobiology of Chagas disease. In this review, Sergio Schenkman and Daniel Eichinger discuss recent data about the structure and function of T. cruzi trans-sialidase.

Differential effect of various inhibitors on four types of rat sialidase

The inhibitory effect of various compounds on the activities of four types of rat sialidase was investigated. 2-Deoxy-2,3-dehydro-N-acetylneuraminic acid and N-acetylneuraminic acid were competitive inhibitors for the sialidases. The former was effective against cytosolic sialidase and intralysosomal sialidase more than two membrane-associated sialidases I and II, the latter being a much weaker inhibitor. A heavy metal ion such as Cu2+ (1 mM) and thiol-modifying 4-hydroxymercuribenzoate (50 microM) caused complete inhibition of the activities of cytosolic sialidase and membrane sialidase I, while no decrease in the activities of intralysosomal sialidase and membrane sialidase II was observed. When 4-nitrophenyloxamic acid and siastatin B, inhibitors of bacterial sialidases, and synthetic thioglycoside GM3 analogue Neu5Ac alpha-s-(2-6)Gal beta(1-4)Glc beta(1-1) ceramide, an inhibitor of influenza virus sialidase, were tested, they did not affect any activity of the rat sialidases. By the differential effect of these inhibitors, the four types of rat sialidase could be discriminated from one another and furthermore from viral and bacterial sialidases.

Isolation and properties of the natural and the recombinant sialidase from Clostridium septicum NC 0054714

The natural sialidase of Clostridium septicum was purified and characterized in parallel with the recombinant enzyme expressed by Escherichia coli. The two enzymes exhibit almost identical properties. The maximum hydrolytic activity was measured at 37 degrees C in 60 mM sodium acetate buffer, pH 5.3. Glycoproteins like fetuin and saponified bovine submandibular gland mucin, most of them having alpha(2-6) linked sialic acids, are preferred substrates, while sialic acids from gangliosides, sialyllactoses, or the alpha(2-8) linked sialic acid polymer (colominic acid) are hydrolysed at lower rates. alpha(2-3) Linkages are more rapidly hydrolysed than alpha(2-6) bonds of sialyllactoses. The cleavage rate is markedly reduced by O-acetylation of the sialic acid moiety. These properties are similar to those of other secreted clostridial sialidases. The enzyme exists in mono-, di- and trimeric forms, the monomer exhibiting a molecular mass of 125 kDa, which is close to the protein mass of 111 kDa deduced from the nucleotide sequence of the cloned gene.