Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The 90-kDa antigen, previously identified by the monoclonal antibody 1G7 to be a stage-specific surface protein of metacyclic trypomastigotes of Trypanosoma cruzi, has been further characterized in this study. Experiments of metabolic labeling with [35S]methionine, [2H]mannose and [3H]galactose revealed that the 90-kDa antigen is the main glycoprotein synthesized by metacyclic forms (G strain). Through pulse-chase experiments with [35S]methionine-labeled metacyclic trypomastigotes, it was found that the antigen is synthesized as a 75-kDa precursor polypeptide that is rapidly processed to the mature 90-kDa molecule. When metacyclic trypomastigotes were treated with tunicamycin, the production of 90-kDa antigen was greatly diminished, and the 75-kDa species, which was also expressed on the cell surface, accumulated. Concanavalin A bound strongly to the 90-kDa antigen, but failed to recognize the 75-kDa polypeptide. Treatment of neuraminidase had no effect on the 90-kDa antigen, whereas digestion by endoglycosidase H generated a polypeptide of 82 kDa. Altogether these data indicate that the 90-kDa antigen is a glycoprotein containing N-linked oligosaccharide side chains of the high-mannose type. The 90-kDa glycoprotein may be involved in the process of host cell invasion, since the internalization of metacyclic forms into Vero cells was partially inhibited by monoclonal antibody 1G7.
Mol Biochem Parasitol 1990 Feb
PMID:The stage-specific 90-kilodalton surface antigen of metacyclic trypomastigotes of Trypanosoma cruzi. 210 76

Human monoclonal IgG1 and IgG3 antibodies specific for the Rh antigen D (anti-D) were tested for their ability to promote the binding of D-positive red cells to peripheral blood monocytes and Fc receptor (FcR)-bearing cell lines (U937, K562 and Daudi). Monocyte-mediated antibody-dependent cell-mediated cytotoxicity and metabolic (chemiluminescent) responses were also determined. By comparing the activity of different cell lines in rosette assays, and by using murine myeloma IgG2a and IgG1 to block FcRI and FcRII respectively, these functional interactions of sensitized red cells (E-IgG1 and E-IgG3) with monocytes or cell lines were shown to be mediated predominantly and perhaps solely by FcRI. E-IgG3 bound to human monocytes and cell lines to a greater extent than E-IgG1. Rosette formation by E-IgG3 was relatively less susceptible to inhibition by fluid-phase murine IgG2a than was rosette formation by E-IgG1. These findings may be due to the long hinge region of IgG3 which enables it to bridge the gap between two negatively charged cells more efficiently than IgG1. Consistent with this hypothesis was the greatly increased rosette formation achieved by treating monocytes or U937 cells with neuraminidase or bromelain, procedures shown to reduce the zeta potential of these cells. The lytic and metabolic activities of untreated human monocytes were also greater towards E-IgG3 than E-IgG1, red cell binding being a prerequisite for these responses. However, after pretreatment of monocytes with neuraminidase, these responses were greater with E-IgG1 than with E-IgG3. Further, the addition of polybrene to non-specifically enhance cell to cell binding also resulted in greater lysis and chemiluminescence with E-IgG1 than with E-IgG3. These results indicate that, although E-IgG3 are more effective than E-IgG1 in promoting red cell binding to monocytes, E-IgG1 are more efficient at activating the lytic and metabolic processes providing the steric disadvantages of the shorter hinge region of cell-bound IgG1 are circumvented.
Mol Immunol 1990 Mar
PMID:Functional interactions of red cells sensitized by IgG1 and IgG3 human monoclonal anti-D with enzyme-modified human monocytes and FcR-bearing cell lines. 211 55

The hemagglutinin-neuraminidase (HN) protein of Newcastle disease virus (NDV) is a type II glycoprotein oriented in the plasma membrane with its amino terminus in the cytoplasm and its carboxy terminus external to the cell. We have previously shown that the membrane insertion of HN protein requires signal recognition particle SRP, occurs cotranslationally, and utilizes the same GTP-dependent step that has been described for secretory proteins, type I proteins, and multispanning proteins (C. Wilson, R. Gilmore, and T. Morrison, Mol. Cell. Biol. 7:1386-1392, 1987; C. Wilson, T. Connolly, T. Morrison, and R. Gilmore, J. Cell Biol. 107:69-77, 1988). The role of the amino-terminal cytoplasmic domain in the faithful membrane insertion of this type II protein was explored by characterizing the membrane integration of a mutant lacking 23 of the 26 amino acids of the cytoplasmic domain. The mutant protein was able to interact with SRP, resulting in translation inhibition, membrane targeting, and membrane translocation, but the efficiency of translocation was considerably lower than for the wild-type HN protein. In addition, a significant proportion of the mutant protein synthesized in the presence of SRP and microsomal membranes was associated with the membrane in an EDTA- and alkali-insensitive manner yet integrated into membranes with its carboxy-terminal domain on the cytoplasmic side of membrane vesicles. Membrane-integrated molecules with this reverse orientation were not detected when the mutant protein was synthesized in the absence of SRP or a functional SRP receptor. Truncated mRNAs encoding amino-terminal segments of the wild-type and mutant proteins were translated to prepare ribosomes bearing arrested nascent chains. The arrested mutant nascent chain, in contrast to the wild-type nascent chain, was also able to insert into membranes in a GTP- and SRP-independent manner. Results suggest that the cytoplasmic domain plays a role in the proper membrane insertion of this type II glycoprotein.
Mol Cell Biol 1990 Feb
PMID:Aberrant membrane insertion of a cytoplasmic tail deletion mutant of the hemagglutinin-neuraminidase glycoprotein of Newcastle disease virus. 215 15

The role of N-linked glycosylation in protein maturation and transport has been studied by using the simian virus 5 hemagglutinin-neuraminidase (HN) protein, a model class II integral membrane glycoprotein. The sites of N-linked glycosylation on HN were identified by eliminating each of the potential sites for N-linked glycosylation by oligonucleotide-directed mutagenesis on a cDNA clone. Expression of the mutant HN proteins in eucaryotic cells indicated that four sites are used in the HN glycoprotein for the addition of N-linked oligosaccharide chains. These functional glycosylation sites were systematically eliminated in various combinations from HN to form a panel of mutants in which the roles of individual carbohydrate chains and groups of carbohydrate chains could be analyzed. Alterations in the normal glycosylation pattern resulted in the impairment of HN protein folding and assembly which, in turn, affected the intracellular transport of HN. The severity of the consequences on HN maturation depended on both the number of deleted carbohydrate sites and their position in the HN molecule. Analysis of the reactivity pattern of HN conformation-specific monoclonal antibodies with the mutant HN proteins indicated that one specific carbohydrate chain plays a major role in promoting the correct folding of HN. Another carbohydrate chain, which is not essential for the initial folding of HN was found to play a role in preventing the aggregation of HN oligomers. The HN molecules which were misfolded, owing to their altered glycosylation pattern, were retained in the endoplasmic reticulum. Double-label immunofluorescence experiments indicate that misfolded HN and folded HN are segregated in the same cell. Misfolded HN forms disulfide-linked aggregates and is stably associated with the resident endoplasmic reticulum protein, GRP78-BiP, whereas wild-type HN forms a specific and transient complex with GRP78-BiP during its folding process.
Mol Cell Biol 1990 May
PMID:Different roles of individual N-linked oligosaccharide chains in folding, assembly, and transport of the simian virus 5 hemagglutinin-neuraminidase. 218 15

Trypanosoma cruzi exhibits a developmentally regulated neuraminidase activity that is inhibited by high-density lipoprotein (HDL). We report here that the infection of culture cells by T. cruzi trypomastigotes is enhanced by HDL in a dose-dependent manner. The enhanced infection is prevented by Vibrio cholerae neuraminidase, an enzyme whose activity is not inhibited by HDL, suggesting that sialic acid is involved in T. cruzi-host interaction. Similar enhancement of infection is also produced by low-density lipoprotein (LDL), which inhibits T. cruzi neuraminidase as well as HDL. Further evidence that the enhancement is due to lipoproteins is provided by the fact that infection of host cells in lipoprotein-deficient medium is less than in normal medium; it can be restored to the higher level by the addition of HDL, LDL or both to the lipoprotein-deficient medium. In view of these results, we propose that HDL and LDL regulate T. cruzi infection in mammalian hosts by inhibiting the parasite neuraminidase activity.
Mol Biochem Parasitol 1990 Jan 15
PMID:High- and low-density lipoproteins enhance infection of Trypanosoma cruzi in vitro. 218 47

gamma-Hydroxybutyric acid (GHB) is a natural compound of mammalian brain synthesized from GABA. The characteristics of its synthesis, transport, release, distribution and turnover, in addition to the presence of a high affinity binding site for this substance in brain are in favor of a modulator role for GHB. The effects of hydrolytic enzymes on the specific binding capacity of GHB have been studied in the present work. Phospholipases A2 and C, neuraminidase and Pronase markedly decrease GHB binding to crude synaptosomal membranes from rat brain. This effect is time and enzyme concentration dependent. Trypsin, under the conditions employed, is less active. The inhibitory effects of phospholipases is correlated with phospholipid hydrolysis. Lysophospholipids, in the absence of bovine fatty acid free serum albumin partially inhibit GHB binding. The action of neuraminidase has been followed by sialic acid release and modifications of the ganglioside profile. The effects of phospholipase C and of neuraminidase are completely different to those on GABA binding sites. These results represent further data concerning the molecular existence of specific GHB binding sites on rat brain membranes.
Mol Cell Biochem 1990 Mar 05
PMID:Effects of phospholipases, proteases and neuraminidase on gamma-hydroxybutyrate binding sites. 218 47

We used the whole-cell configuration of the patch-clamp technique and cultured ventricular myocytes from 7-day embryonic chicks to test the hypothesis that sialic acid residues (NANA) constitute the negative surface charge associated with delayed rectifier potassium channels. Delayed rectifier current (iK) was elicited at potentials between -40 and +60 mV. The existence of negative fixed charges close to the "gating sensor" was confirmed by a 6.8-mV negative shift of the half-activation potential (V1/2) following a 10-fold reduction of divalent cations and a 22.6-mV position shift following the addition of 10 mM NiCl2. An 8.4-mV increase in the Boltzmann equation slope factor (k) in the former experiment and a 5.5-mV decline in the latter suggested that the surface charge is not uniformly distributed. We used a high performance liquid chromatography procedure to detect freed sarcolemmal NANA and found that 71-88% was released by neuraminidase (0.2-2.0 U/ml) during 1-h treatments. Such treatments had no significant effect upon the amplitudes of iK or V1/2. On the other hand, k was increased significantly by the enzyme (2.0 U/ml), but only when Ca2+ was present. Finally, 1-h pre-treatments with neuraminidase (2.0 U/ml) had no effect on the positive shift of V1/2 induced by Ni2+. We conclude that although sarcolemmal NANA may bind Ca2+, it does not constitute the surface charge of delayed rectifier potassium channels.
J Mol Cell Cardiol 1990 Nov
PMID:Sialic acid and the surface charge of delayed rectifier potassium channels. 228 87

Cell surface forms of Qa-6 class I molecules are biochemically indistinguishable from Qa-2 although Qa-6 maps telomeric to Qa-2 with the recombinant strain B6.K2. Analysis of appropriate F1 strains did not demonstrate the presence of a trans acting factor that could modify the Qa-2 molecule to produce the Qa-6 determinant. Also, neither a neighboring cell surface molecule nor oligosaccharides were found to block the recognition of the Qa-6 determinant in Qa-2+,6- strains. The 2-D gel profiles of neuraminidase or endoglycosidase treated anti-Qa-2 immunoprecipitates from lysates of cell surface iodinated Qa-2+,6+ strains revealed an additional basic polypeptide which was absent from that of Qa-2+,6- strains. Thus, differential sialylation/glycosylation of Qa-2 molecules masks detection of Qa-2 antigen heterogeneity when cell surface forms are analyzed. Qa-6+ phenotype associated polypeptides were also found at various stages of post-translational processing in cells metabolically labeled in the presence and absence of tunicamycin. Northern analyses using Q7 and Q9 specific oligonucleotide probes revealed appropriate sized transcripts for both genes in the Qa-2+,6+ strain B6 but only Q9 in the Qa-2+,6- strain B6.K2. These data demonstrate that there is structural heterogeneity in Qa-2 antigens expressed by Qa-2+,6+ and Qa-2+,6- strains which results from differential expression of the Q7 and Q9 genes.
Mol Immunol 1990 Jun
PMID:Biochemical differences in Qa-2 antigens expressed by Qa-2+,6+ and Qa-2+,6- strains. Evidence for differential expression of the Q7 and Q9 genes. 238 28

Mammalian A2-adenosine receptor binding subunits (A2AR) can be visualized by covalent labeling with the photoaffinity crosslinking ligand 125I-2-[4-[2-[2-[(4-aminophenyl)methylcarbonylamino] ethylaminocarbonyl]ethyl]phenyl]ethylamino-5'-N-ethylcarboxamidoad enosine or directly with the azide derivative described in this paper. The protein comprising the A2-adenosine receptor binding subunit migrates with a Mr of 45,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In this study, the glycoproteins representing the radiolabeled A1- and A2-adenosine receptor binding subunit from bovine brain were compared by partial peptide maps and following treatment with exo- and endoglycosidases. Peptide maps using two separate proteases reveal that the A1- and A2-adenosine receptor binding subunits share no common peptide fragments by two-dimensional gel electrophoresis. Endoglycosidase F treatment of labeled A2AR results in a single labeled peptide of Mr 38,000 without intermediate peptides, suggesting a single N-linked carbohydrate chain. The labeled A2AR demonstrates a sensitivity to neuraminidase, as evidenced by an increased mobility on gel electrophoresis, suggesting the receptors contain a glycan component containing terminal sialic acid. Treatment of the labeled A2AR with alpha-mannosidase reveals two distinct populations of A2ARs, one of which is sensitive and the other resistant to the enzyme. The nonadditivity of sequential treatments with the two exoglycosidases suggests, a heterogeneous population of A2AR containing either complex- or high mannose-type carbohydrate chains. These data suggest the A2AR is a Mr 45,000 glycoprotein with a single carbohydrate chain of either the complex or high mannose type. In addition, the A1- and A2ARs are distinct glycoproteins, as evidenced by their differing molecular weights (before and after deglycosylation) and distinct peptide maps.
Mol Pharmacol 1990 Aug
PMID:Glycoprotein nature of the A2-adenosine receptor binding subunit. 238 30

New crystalline forms of tetrameric neuraminidase heads from two strains (B/Lee/40 and B/mem/89) of type B human influenza virus were obtained and the crystals diffracted using X-rays to 2.5 A resolution without lattice disorder. The new B/Lee/40 crystalline form is tetragonal, space group P42(1)2, with unit cell dimensions a = 123.8 A, c = 71.8 A. The B/mem/89 crystalline form is also tetragonal, space group I422, with unit cell dimensions a = 122.9 A, c = 164.4 A. There is one neuraminidase monomer per asymmetric unit in both forms.
J Mol Biol 1990 Aug 05
PMID:New crystalline forms of neuraminidase of type B human influenza virus. 238 63


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