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)

Several mammalian sialidases have been cloned so far and here we describe the identification and expression of a new member of the human sialidase gene family. The NEU4 gene, identified by searching sequence databases for entries showing homologies to the human cytosolic sialidase NEU2, maps in 2q37 and encodes a 484-residue protein. The polypeptide contains all the typical sialidase amino acid motifs and, apart from an amino acid stretch that appears unique among mammalian sialidases, shows a high degree of homology for NEU2 and the plasma membrane-associated (NEU3) sialidases. RNA dot-blot analysis showed a low but wide expression pattern, with the highest level in liver. Transient transfection in COS7 cells allowed the detection of a sialidase activity toward the artificial substrate 4MU-NeuAc in the acidic range of pH. Immunofluorescence staining and Western blot analysis demonstrated the association of NEU4 with the inner cell membranes.
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PMID:Molecular cloning and characterization of NEU4, the fourth member of the human sialidase gene family. 1496 70

Three different mammalian sialidases have been described as follows: lysosomal (Neu1, gene NEU1), cytoplasmic (Neu2, gene NEU2), and plasma membrane (Neu3, gene NEU3). Because of mutations in the NEU1 gene, the inherited deficiency of Neu1 in humans causes the severe multisystemic neurodegenerative disorder sialidosis. Galactosialidosis, a clinically similar disorder, is caused by the secondary Neu1 deficiency because of genetic defects in cathepsin A that form a complex with Neu1 and activate it. In this study we describe a novel lysosomal lumen sialidase encoded by the NEU4 gene on human chromosome 2. We demonstrate that Neu4 is ubiquitously expressed in human tissues and has broad substrate specificity by being active against sialylated oligosaccharides, glycoproteins, and gangliosides. In contrast to Neu1, Neu4 is targeted to lysosomes by the mannose 6-phosphate receptor and does not require association with other proteins for enzymatic activity. Expression of Neu4 in the cells of sialidosis and galactosialidosis patients results in clearance of storage materials from lysosomes suggesting that Neu4 may be useful for developing new therapies for these conditions.
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PMID:Neu4, a novel human lysosomal lumen sialidase, confers normal phenotype to sialidosis and galactosialidosis cells. 1521 28

Based on the human cDNA sequence predicted to represent the NEU4 sialidase gene in public databases, a cDNA covering the entire coding sequence was isolated from human brain and expressed in mammalian cells. The cDNA encodes two isoforms: one possessing an N-terminal 12-amino-acid sequence that is predicted to be a mitochondrial targeting sequence, and the other lacking these amino acids. Expression of the isoforms is tissue specific, as assessed by reverse transcription-PCR. Brain, muscle and kidney contained both isoforms; liver showed the highest expression, and the short form was predominant in this organ. In transiently transfected COS-1 cells, enzyme activity was markedly increased with gangliosides as well as with glycoproteins and oligosaccharides as substrates compared with the control levels. This differs from findings with other human sialidases. Although the isoforms were not distinguishable with regard to substrate specificity, they exhibited differential subcellular localizations. Immunofluorescence microscopy and biochemical fractionation demonstrated that an exogenously expressed haemagglutinin-tagged long form of NEU4 was concentrated in mitochondria in several human culture cell types, whereas the short form was present in intracellular membranes, indicating that the sequence comprising the N-terminal 12 amino acid residues acts as a targeting signal for mitochondria. Co-localization of the long form to mitochondria was further supported by efficient targeting of the N-terminal region fused to enhanced green fluorescent protein, and by the targeting failure of a mutant with an amino acid substitution in this region. NEU4 is possibly involved in regulation of apoptosis by modulation of ganglioside G(D3), which accumulates in mitochondria during apoptosis and is the best substrate for the sialidase.
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PMID:Evidence for mitochondrial localization of a novel human sialidase (NEU4). 1584 5

In mammalian cells, four types of sialidase have been described and found to behave in different ways during carcinogenesis. We previously demonstrated that a human sialidase associated with plasma membranes (NEU3) is up-regulated in human colon cancer and is involved in suppression of apoptosis. Here we document altered expression of another human sialidase, the recently identified NEU4, and evidence of its influence on the malignant phenotype in colon cancers. Human colon mucosa was relatively rich in NEU4, which has been observed to possess short and long isoforms, but hardly contained the latter form. In clear contrast to the NEU3 case, the levels of mRNA for this sialidase were found by quantitative RT-PCR to be markedly decreased in colon cancers. In cultured human colon cancer cells, the enzyme was up-regulated in the early stage of apoptosis induced by either the death ligand TRAIL or serum-depletion, and transfection of NEU4 resulted in acceleration of apoptosis and in decreased invasion and motility. The siRNA-mediated NEU4 targeting, on the other hand, caused a significant inhibition of apoptosis and promotion of invasion and motility. Lectin blot analyses revealed that desialylated forms of nearly 100 kDa glycoproteins were prominently increased with PNA in NEU4 transfectants, whereas only slight changes in glycolipids were detected as assessed by thin layer chromatography. These results suggest that NEU4 plays important roles for maintenance of normal mucosa mostly through desialylation of glycoproteins and that down-regulation may contribute to invasive properties of colon cancers.
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PMID:Down-regulation of sialidase NEU4 may contribute to invasive properties of human colon cancers. 1727 19

Cell surface carbohydrate expression strongly influences the biological characteristics of cancer cells. Especially, it is known that the change of sialic acid expression could be related to the invasive and metastatic potentials of tumors. This study aimed to investigate sialidase expression of ovarian cancer cells and to evaluate the relationship between plasma membrane-associated sialidase (NEU3) expression and various clinicopathological factors in ovarian clear cell adenocarcinoma patients. In 18 cell lines derived from human ovarian cancers (including clear cell, mucinous, and serous adenocarcinoma), sialidase mRNA expression was evaluated by RT-PCR. NEU1 and NEU3 expression levels were found to be elevated in most cell lines while NEU2 and NEU4 expression was rarely elevated. Interestingly, NEU3 expression was detected in all clear cell adenocarcinoma cell lines. In 71 patients with ovarian clear cell adenocarcinoma, treated at Keio University Hospital from February 1983 to February 2002, NEU3 expression was examined by immunohistochemical staining of surgical specimens and clinicopathological factors were reviewed. NEU3 expression was found to be positive in 77.5% of all cases. Furthermore, a high level of NEU3 expression was significantly correlated with T3 factor of pTNM classification on univariate and multivariate analysis. This is the first report to show that NEU3 is expressed in most of ovarian clear cell adenocarcinoma. And our results show that NEU3 expression is correlated with T factor (pTNM classification) in ovarian clear cell adenocarcinoma.
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PMID:Expression of NEU3 (plasma membrane-associated sialidase) in clear cell adenocarcinoma of the ovary: its relationship with T factor of pTNM classification. 1747 74

Sialidases remove sialic acid residues from various sialo-derivatives. To gain further insights into the biological roles of sialidases in vertebrates, we exploited zebrafish (Danio rerio) as an animal model. A zebrafish transcriptome- and genome-wide search using the sequences of the human NEU polypeptides as templates revealed the presence of seven different genes related to human sialidases. neu1 and neu4 are the putative orthologues of the mammalian sialidases NEU1 and NEU4 respectively. Interestingly, the remaining genes are organized in clusters located on chromosome 21 and are all more closely related to mammalian sialidase NEU3. They were thus named neu3.1, neu3.2, neu3.3, neu3.4 and neu3.5. Using RT-PCR (reverse transcription-PCR) we detected transcripts for all genes, apart from neu3.4, and whole-mount in situ hybridization experiments show a localized expression pattern in gut and lens for neu3.1 and neu4 respectively. Transfection experiments in COS7 (monkey kidney) cells demonstrate that Neu3.1, Neu3.2, Neu3.3 and Neu4 zebrafish proteins are sialidase enzymes. Neu3.1, Neu3.3 and Neu4 are membrane-associated and show a very acidic pH optimum below 3.0, whereas Neu3.2 is a soluble sialidase with a pH optimum of 5.6. These results were further confirmed by subcellular localization studies carried out using immunofluorescence. Moreover, expression in COS7 cells of these novel zebrafish sialidases (with the exception of Neu3.2) induces a significant modification of the ganglioside pattern, consistent with the results obtained with membrane-associated mammalian sialidases. Overall, the redundancy of sialidases together with their expression profile and their activity exerted on gangliosides of living cells indicate the biological relevance of this class of enzymes in zebrafish.
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PMID:Molecular cloning and biochemical characterization of sialidases from zebrafish (Danio rerio). 1770 49

We here report the design and synthesis of selective human lysosomal sialidase (NEU1) inhibitors. A series of amide-linked C9 modified DANA (2-deoxy-2,3-dehydro-N-acetylneuraminic acid) analogues were synthesized and their inhibitory activities against all four human sialidases (NEU1-NEU4) were determined. Structure-based approach was used to investigate the basis of selectivity of the compounds with experimentally observed activity. Results from the present study are found to be informative in a qualitative manner for the further design of isoform selective human sialidase inhibitors for therapeutic value.
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PMID:Design, synthesis, and biological evaluation of human sialidase inhibitors. Part 1: selective inhibitors of lysosomal sialidase (NEU1). 1806 75

Recent advances in the sialidase biology have clarified the role of human sialidases (NEU 1 to NEU4) in the development of various disease states such as cancer, diabetes and arteriosclerosis. Isoform selective human sialidase inhibitors could be a therapeutic tool or molecular probes for the exploration of the specific functions of human sialidases. In the present study, de novo design based virtual screening was performed to find a new class of human sialidase inhibitors using the experimental crystal structure of NEU2 isoform. A few of nitro benzene and fluoro benzoic acid were identified and a series of 4-acetamido-5-acylamido-2-fluoro benzoic acids were synthesized and, the inhibitory activity of all these compounds against all human sialidase enzymes was evaluated. All these compounds were found to have a poor inhibitory activity and only NEU2 showed more sensitivity to this series of compounds as compared to other isoforms. Molecular docking was performed to gain insight regarding the binding mode of these inhibitors and thereby provided valuable information for our study on the design of selective human sialidase inhibitors further.
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PMID:Human sialidase inhibitors: design, synthesis, and biological evaluation of 4-acetamido-5-acylamido-2-fluoro benzoic acids. 1945 Sep 82

Sialidases are widely distributed glycohydrolytic enzymes removing sialic acid residues from glycoconjugates. In mammals, several sialidases with different subcellular localizations and biochemical features have been described. NEU4, the most recently identified member of the human sialidase family, is found in two forms, NEU4 long and NEU4 short, differing in the presence of a 12-amino-acid sequence at the N-terminus. Contradictory data are present in the literature about the subcellular distribution of these enzymes, their membrane anchoring mechanism being still unclear. In this work, we investigate the human NEU4 long and NEU4 short membrane anchoring mechanism and their subcellular localization. Protein extraction with Triton X-114 and sodium carbonate and cross-linking experiments demonstrate that both forms of NEU4 are extrinsic membrane proteins, anchored via protein-protein interactions. Moreover, through confocal microscopy and subcellular fractionation, we show that the long form localizes in mitochondria, while the short form is also associated with the endoplasmic reticulum. Finally, mitochondria subfractionation experiments suggest that NEU4 long is bound to the outer mitochondrial membrane.
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PMID:Human sialidase NEU4 long and short are extrinsic proteins bound to outer mitochondrial membrane and the endoplasmic reticulum, respectively. 1979 20

The mammalian neuraminidase (NEU) enzymes are found in diverse cellular compartments. Members of the family, such as NEU2 and NEU1, are cytosolic or lysosomal, while NEU3 and NEU4 are membrane-associated. NEU enzymes that act on substrates in the plasma membrane could modulate cellular signaling, cell surface glycoforms and the composition of plasma membrane glycolipids. Therefore, their substrates and mechanism of action are of interest for discerning their physiological roles. We have studied the structure of the human NEU3 using molecular modeling to predict residues involved in the recognition and hydrolysis of glycolipid substrates. To test the model, we have used site-directed mutagenesis of the recombinant protein. Enzymatic studies of the relative activity of these mutants, as well as their pH profiles and inhibition by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, are reported. Using nuclear magnetic resonance spectroscopy, we confirmed that the enzyme is a retaining exo-sialidase, and we propose that the key catalytic residues of the enzyme consist of the general acid-base D50 and the nucleophilic Y370-E225 pair. Mutations of residues expected to interact directly with the sialic acid N5-acetyl (A160, M87, I105) and C7-C9 glycerol side-chain (E113, Y179, Y181) reduced enzymatic activity. We identified several active mutants of the enzyme which contain modifications at the periphery of the active site. Truncations at the N- or C-terminus of more than 10 residues abolished enzyme activity. We propose a catalytic mechanism consistent with the data and identify residues that contribute to glycolipid recognition.
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PMID:Insight into substrate recognition and catalysis by the human neuraminidase 3 (NEU3) through molecular modeling and site-directed mutagenesis. 2051 Dec 47


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