Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.1.53 (sialidase)
2,694 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An isolate of Streptococcus intermedius from a brain abscess showed neuraminidase (sialidase), beta-D-galactosidase, N-acetyl-beta-D-glucosaminidase and N-acetyl-beta-D-galactosaminidase activities. The optimal pH values of these enzymes were 5.5-6.0, 5.5-6.0, 5.0-5.5 and 5.0-5.5, respectively. The km of the enzymes varied according to whether the type of substrate was chromogenic or fluorogenic; sialidase was most active at the lowest substrate concentrations, with a km of 0.01 mM. In semi-defined medium, with porcine gastric mucin--a model glycoprotein--as the sole source of fermentable carbohydrate, levels of the glycosidases were significantly increased. Addition of glucose to the mucin-containing medium, or growth of cells in media supplemented with glucose alone, repressed glycosidic activities and the majority of these were cell-associated. S. intermedius cells from cultures grown with mucin were able, simultaneously, to transport via sugar:phosphoenolpyruvate phosphotransferase (PTS) systems, monosaccharides which are constituents of carbohydrate side chains of glycoproteins. These cells also possessed significant levels of neuraminate-pyruvate lyase, involved in the intracellular catabolism of neuraminic acid; this was absent from cells grown with glucose. These mechanisms, collectively, may facilitate the persistence and growth of S. intermedius in vivo.
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PMID:Production of specific glycosidase activities by Streptococcus intermedius strain UNS35 grown in the presence of mucin. 806 38

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)
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PMID:Trans-sialidase, SAPA amino acid repeats and the relationship between Trypanosoma cruzi and the mammalian host. 808 53

Infective trypomastigote stages of the obligate intracellular protozoan parasite Trypanosoma cruzi are capable of entering virtually any mammalian cell in vitro. Entry is a complex process, involving initial parasite attachment to surface moieties of the target cell, internalization of the parasite via formation of a vacuole, and finally disruption of the vacuolar membrane to permit access of the parasite to the host cell cytoplasm. Attachment requires parasite metabolic energy. At sites of parasite entry recruitment of host cell lysosomes may occur, and lysosomal membrane components contribute prominently to formation of the parasitophorous vacuole. Parasite escape from the vacuole depends upon vacuolar acidification and is mediated by the coordinated action of a parasite-derived neuraminidase/trans-sialidase that is capable of desialylating host-derived vacuolar membrane constituents, and a parasite-derived trans-membrane pore-forming protein. Dissection of the entry process at both the organellar and molecular level is providing fundamental and complementary insights into microbial pathogenesis and cell biology.
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PMID:Trypanosoma cruzi: mechanisms for entry into host cells. 825 84

We have studied the trans-sialidase from insect forms of Trypanosoma cruzi growing in axenic culture. Log phase epimastigotes expressed little or no trans-sialidase activity, and were unable to incorporate exogenous sialic acid. Transsalidase started to be expressed at the late logarithmic phase, with specific activity increasing steadily as the culture reached the stationary phase. Trans-sialidase was purified from the late log phase epimastigote culture, which contained less than 2% of metacyclic forms, yielding a glycoprotein that migrated as a single 90-kDa band in sodium dodecyl sulfate gels. This enzyme features: (1) no reaction with antibodies against the peptide repeats present in the carboxy-terminal of trypomastigote trans-sialidase; (2) positive reaction with antibodies raised against a fragment of trypomastigote trans-sialidase that contains the active site; (3) similar kinetic properties and identical acceptor-donor specificity when compared to the trypomastigote enzyme; and (4) neuraminidase activity in the absence of acceptors. Upon differentiation into metacyclic forms, a trans-sialidase activity containing the carboxy-terminal repeats of the trypomastigote enzyme was released into the medium. These results suggest that epimastigotes express a developmentally regulated trans-sialidase that contains the same catalytic site but lacks the tandem amino acid repeats typical of trypomastigote trans-sialidase.
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PMID:Trans-sialidase from Trypanosoma cruzi epimastigotes is expressed at the stationary phase and is different from the enzyme expressed in trypomastigotes. 825 37

The sialidase (neuraminidase) inhibitor 4-guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid (4-guanidino-Neu5Ac2en) has been examined for the ability to inhibit the growth of a wide range of influenza A and B viruses in vitro in comparison with amantadine, rimantadine, and ribavirin. 4-Guanidino-Neu5Ac2en inhibited plaque formation by laboratory-passaged strains of influenza A and B viruses, with 50% inhibitory concentrations ranging from 0.005 to 0.014 microM. A wider range of values (0.02 to 16 microM) was obtained with more recent clinical isolates, but in all cases 4-guanidino-Neu5Ac2en inhibited influenza A and B virus replication at lower concentrations than amantadine, rimantadine, or ribavirin. Inhibition by 4-guanidino-Neu5Ac2en was not obviously affected by the passage history of the viruses or by resistance to amantadine or rimantadine. 4-Guanidino-Neu5Ac2en was a very potent inhibitor of the sialidases of all the influenza viruses examined, with 50% inhibitory concentrations ranging from 0.00064 to 0.0079 microM. No cytotoxicity was observed with 4-guanidino-Neu5Ac2en at up to 10 mM. 4-Guanidino-Neu5Ac2en therefore represents a new potent and selective inhibitor of influenza A and B virus sialidase activity and replication in vitro.
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PMID:4-Guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid is a highly effective inhibitor both of the sialidase (neuraminidase) and of growth of a wide range of influenza A and B viruses in vitro. 836 79

We have used a Chinese hamster ovary cell mutant (Lec2) that express much less sialic acid on the surface than the parental cell line (Pro5) to investigate whether sialic acid plays a role during cell invasion by Trypanosoma cruzi. Trypomastigotes derived from a tissue culture (corresponding to bloodstream trypomastigotes) and metacyclic trypomastigotes (corresponding to infective stages of the insect vector) invaded the Lec2 mutant less efficiently than the parental cell line. Invasion of the Lec2 mutant cells could be restored to the Pro5 level by resialylation of the mutant cells with T. cruzi trans-sialidase and sialyllactose. Conversely, pretreatment of the Pro5 parental cells with bacterial neuraminidase decreased invasion. These results indicate that sialic acid associated with the host cell contributes to invasion by T. cruzi.
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PMID:Mammalian cell sialic acid enhances invasion by Trypanosoma cruzi. 838 72

Cell surface carbohydrates have been shown to be altered during cellular differentiation. Alveolar type II (ATII) cells in culture gradually lose their differentiated phenotype. Therefore, the aim of this study was: (1) to characterize changes in terminal carbohydrates of cell surface glycoproteins of rat ATII cells cultured for 1 to 5 days on plastic, and (2) to assess the concomitant changes in sialidase and sialyltransferase activity of ATII cell homogenates. Cells were surface-labeled with potassium-[3H]-borohydride after oxidation by sodium periodate at millimolar concentrations, galactose oxidase or neuraminidase plus galactose oxidase, allowing for the specific labeling of terminal sialic acids, terminal galactose/N-acetylgalactosamine (Gal/GalNAc), or terminal an penultimate Gal/GalNAc residues, respectively. Glycoproteins were separated by SDS-PAGE. On day 1, cells were heavily coated with sialic acids, since no labeling could be introduced with galactose oxidase alone. From day 1 to day 5, we observed a selective and progressive desialylation of two glycoproteins (200 and 165 kD). At the same time, the ATII cells' sialidase activity (pH 4.2) exhibited an 8-fold increase (60.3 +/- 4.0 pmol/min/mg protein on day 1 versus 406.9 +/- 3.7 pmol/min/mg protein on day 5), whereas the sialyltransferase activity increased 2-fold (212 +/- 8 fmol/min/mg protein on day 1 versus 395 +/- 82 fmol/min/mg protein on day 5) and the supernatant sialidase activity was unchanged (2.8 +/- 0.7 pmol/min/ml on day 5). Thus, the phenotypic changes of ATII cells in primary culture are accompanied by a partial cell surface desialylation and an increase in intracellular sialidase activity.
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PMID:Cell surface carbohydrates of rat alveolar type II cells in primary culture. 842 6

Developmental preadaptation of virulent stages of Trypanosoma cruzi correlates with their ability to survive and establish infection in mammalian hosts. Infective trypomastigote stages must first preadapt to survival in the extracellular milieu and then to the rigors of establishing an intracellular infection. Selected phenotypic variations in evading host defences have been correlated with expression of stage-specific proteins or functions. Resistance of trypomastigotes to complement-mediated killing correlates with the presence of a stage-specific molecule that exhibits an analogous function to mammalian decay-accelerating factor, and with the presence of a neuraminidase/trans-sialidase that transfers sialic acid moieties to the parasite surface, thereby enabling it to avoid complement activation. Trypomastigotes enter cells by a mechanism that involves sorting of cell surface receptors and avoids eliciting a respiratory burst. Once within a membrane-bound vacuole, which undergoes acidification, the neuraminidase/trans-sialidase and an acid-active, transmembrane pore-forming protein are released by the parasite and are capable of acting together to accelerate rupture of the vacuolar membrane and the parasite's escape into the cytoplasm of the host cell. Escape from the parasitophorous vacuole allows virulent stages of T. cruzi to avoid compartmental, non-oxidative killing mechanisms such as degradation by lysosomal hydrolases.
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PMID:Developmentally-regulated virulence factors of Trypanosoma cruzi and their relationship to evasion of host defences. 846 94

Influenza A viruses exhibit segmented nucleic acid coding for eight different proteins, two of them as glycoproteins exposed on their lipoprotein envelopes, hemagglutinin (HA) and neuraminidase (NA). Hemagglutinin exhibits receptor-binding activity while neuraminidase develops sialidase cleavage activity which acts on cell receptors. Influenza A strains responsible for human, avian, equine and porcine respiratory infections all over the world present antigenically different hemagglutinin (H1 to H14) and neuraminidase (N1 to N9) structures on their surface. The objective of the present investigation was to study the role of N2, N8, and N9, antigenically diverse neuraminidase structures of human (N2) and animal (N8 and N9) influenza viruses, in the receptor-binding process. Receptor-binding activity of N2 and N8 was analyzed by crossed tests using H3N2 and H3N8 antisera and the hemagglutination inhibition test as a model. Hemagglutinating activity of antigenically different N2 and N8 structures was demonstrable and was inhibited by homologous antisera (N2-H3N2, N8-H3N8) but not by heterologous antisera (N2-H3N8,N8-H3N2). This previously demonstrated N9 hemagglutinating activity was analyzed for receptor-binding specificity using hemagglutination tests and NeuAc alpha2,3Gal and NeuAc alpha2,6Gal derivatized erythrocytes. This highly purified N9 strain was obtained from a virus strain isolated from terns by Dr. Peter Colman (CSIRO Division of Biomolecular Engineering, Parkville, Victoria, Australia). It exhibited receptor-binding specificity for NeuAc alpha2,3Gal sequences, a property similar to that observed in hemagglutinins from avian strains. These results indicate the importance of antigenically different neuraminidase structures as alternative agents for developing receptor-binding activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The role of antigenically different virus neuraminidases as structures implicated in receptor-binding processes. 854 43

GG167 (4-guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid) is a novel viral neuraminidase (sialidase) inhibitor which, following intranasal administration in ferrets, is at least 100 to 1,000 times more effective than ribavirin and amantadine against influenza A and B viruses. It retains its activity even when treatments are delayed until 24 h postinfection and has no effect on the serum antibody response to infection.
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PMID:GG167 (4-guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid) is a potent inhibitor of influenza virus in ferrets. 858 52


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