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The composition and proposed subunit structure of egg-white beta-ovomucin. The isolation of an unreduced soluble ovomucin.

1. New preparations of reduced carboxymethylated beta-ovomucin (S-carboxymethyl-beta-ovomucin) were homogeneous by sedimentation analysis, analytical sedimentation to equilibrium in CsCl gradients, and disc electrophoresis in sodium dodecyl sulphate. 2. Degradation of S-carboxymethyl-beta-ovomucin with either CNBr or trypsin indicated the presence of a subunit (approx. mol. wt. 112300). 3. Electron microscopy showed that S-carboxymethyl-beta-ovomucin consisted of chains of globular units (approx. mol. wt. 103 000). IN 6M-guanidinium chloride S-carboxymethyl-beta-ovomucin existed mainly as an aggregate (mol. wt. 720 000). 4. S-Carboxymethyl-beta-ovomucin contained ester sulphate (4.24%, W/W) and carbohydrate (60%, W/W), which consisted of large amounts of galactose (22%, W/W), galactosamine (8.9%, W/W) and sialic acid (10.6%, W/W). 5. An unreduced soluble fibrous component (component SGH) extracted from crude ovomucin precipitate with 5M-guanidinium chloride contained beta-ovomucin (approx. 70%, W/W). By using the Scheraga-Mandelkern equation the molecular weight of component SGH was calculated to be 11.5 times 10(6).

Amino Acids↗

The supramolecular organization of ovomucin. Biophysical and morphological studies.

Ovomucin participates in the ovomucin-gel-forming properties because of its shape and its ability to interact in a specific spatial organization. Purified from chicken egg-white by exclusion chromatography with Sephacryl S-300 and Sepharose CL-2B and analysed by light-scattering, it exhibited an Mr of about 40 x 10(6). This large Mr can be explained by the aggregation of polymers that can be degraded into 3 x 10(6)-Mr fragments by reduction with dithiothreitol. The values for hydrodynamic parameters such as Mr, radius of gyration, hydrodynamic radius, mass per unit length and combinations of them suggested that ovomucin is a linear and highly flexible molecule conferring upon it a random-coil-like structure in 0.2 M-NaCl solution. Analysis of the ovomucin molecules by electron microscopy revealed its linear character but also indicated a lower Mr than that obtained in the light-scattering experiments. By temperature-induced non-specific aggregation of an ovomucin solution containing other globular egg proteins, an attempt was made to find out what conditions are required for gel formation and to examine the quality of aggregation that is obtained under these conditions. Results show that the viscosity of the solution did not increase after heat treatment. Apparently, in the ovomucin gel, specific spatial organization of the ovomucin molecules is required for hydrogel formation.

Animals↗

Studies on the composition of egg-white ovomucin.

1. Purified ovomucin was isolated as an insoluble glycoprotein complex from thick egg white. 2. A homogeneous glycoprotein, designated alpha-ovomucin, of molecular weight 210000 and containing N-acetylglucosamine (6.7%, w/w), N-acetylgalactosamine (0.6%, w/w), galactose (1.8%, w/w), mannose (4.6%, w/w), N-acetylneuraminic acid (1.0%, w/w) and sulphate (0.7%, w/w), was isolated from preparations of reduced ovomucin by sedimentation equilibrium in a density gradient of caesium chloride formed in the presence of 4m-guanidine hydrochloride. 3. A carbohydrate-rich fraction, designated beta-ovomucin (which is homogeneous by sedimentation-velocity analysis in 5m-guanidine hydrochloride but which is heterogeneous by analytical sedimentation equilibrium in a density gradient of caesium chloride in the presence of 4m-guanidine hydrochloride), containing N-acetylglucosamine (11.0%, w/w), N-acetylgalactosamine (8.7%, w/w), galactose (19.2%, w/w), mannose (4.1%, w/w), N-acetylneuraminic acid (13.8%, w/w) and sulphate (2.7%, w/w), was also obtained from preparations of reduced ovomucin by the density-gradient method. 4. Mild acid hydrolysis of the unfractionated ovomucin complex showed that N-acetylneuraminic acid occupied a terminal position of the oligosaccharide chains. 5. Alkaline beta-elimination reactions with the unfractionated ovomucin complex indicated that N-acetylgalactosamine was linked by alkali-labile bonds to hydroxy amino acids.

Amino Acids↗

Comparison of different egg albumen fractions as sources of ovomucin.

Ovomucin was fractionated from whole egg albumen, thick egg albumen, liquid egg albumen, and a liquid egg albumen filtration byproduct by using the isoelectric precipitation method. The amounts of ovomucin measured in the above-mentioned fractions were 280, 340, 500, and 520 mg per 100 g of albumen, respectively. There was great variation between the beta-ovomucin contents of the different albumen fractions. Whole egg albumen contained about 25 mg of beta-ovomucin in 100 g of albumen, whereas thick egg albumen, liquid egg albumen, and the filtration byproduct contained about 1.5, 3, and 5 times more beta-ovomucin, respectively, as compared to whole egg albumen. The results indicate that both the liquid egg albumen fraction and especially the filtration byproduct fraction appear to be potential sources of ovomucin when it is used as an ingredient for functional foods.

Carbohydrates↗

An ovomucin-like protein on the surface of migrating primordial germ cells of the chick and rat.

A mucin was discovered on the surface of migratory primordial germ cells (PGCs) from chick and rat embryos by means of two monoclonal antibodies. The protein was found to be identical or closely related to ovomucin, a 600 X 10(3) relative molecular mass glycoprotein, and a major constituent of the vitelline membrane of the avian yolk. Based on its resemblance to ovomucin it is referred to as ovomucin-like protein (OLP). The OLP was expressed on PGCs from E3 to E7 female, and from E3 to E12 male chick embryos as the PGCs migrate and colonize the gonadal ridges. After the PGCs have settled in the gonads, they no longer express OLP. In tissue cultures of dissociated cells from E6 gonads, OLP was present only on cells that were positive for PAS staining, the standard histological method to identify PGCs in the chick embryo. Since unfixed PGCs were recognized by the antibodies, at least part of the OLP is localized on the cell surface. The anti-OLP antibodies also stained PGCs in the gonads of the rat embryo, showing that the expression of this antigen on PGCs is phylogenetically conserved. Ovomucin isolated from vitelline membrane prevented adhesion of fibroblasts but not PGCs when used a as a substratum in vitro. The anti-adhesive quality of the mucin resides in the sialic acid residues of the carbohydrate side chains. We propose that OLP has a similar anti-adhesive quality as the ovomucin from vitelline membrane, and that this anti-adhesive property is important to prevent precocious adhesion of migrating PGCs to blood vessel walls and to connective tissue in the mesentery as they migrate toward the gonadal ridges.

Animals↗

Interactions involved in ovomucin gel-forming properties: a rheological-biochemical approach.

Different kinds of interactions involved in the properties of ovomucin gel formation from hen egg white were studied by combining physical and biochemical methods. A decrease in viscosity of the ovomucin gel was observed when it was subjected to chymotrypsin or sonication treatment. The viscosity decrease correlated with a change from non-Newtonian to Newtonian properties of the ovomucin gel. By treatment of the gel with either 5 M guanidinium HCl, 6 M urea, or 5% sodium dodecyl sulfate a change from non-Newtonian to Newtonian properties was also obtained. Although high ionic strength or sialic acid liberation from the ovomucin gel by neuraminidase treatment provoked a decrease in viscosity, it was not followed by a change in non-Newtonian properties. The results obtained suggest that different noncovalent interactions might be involved in gel formation. Electrostatic interactions (partially destroyed by sialic acid removal or 2 M NaCl) and hydrophobic interactions might be responsible for protein-mucin and mucin-mucin interactions. Other bonds susceptible to chymotrypsin treatment and sonication would be involved in the interaction between mucin subunits.

Animals↗

Two-step chromatographic procedure for the purification of hen egg white ovomucin, lysozyme, ovotransferrin and ovalbumin and characterization of purified proteins.

An improved procedure is described involving gel permeation and anion-exchange chromatography for the purification of four major hen egg white proteins. The procedure involves a first-step purification of ovomucin and lysozyme by gel permeation on a Superose 6 Prep Grade column. In the second step, anion-exchange chromatography on Q Sepharose Fast Flow led to the isolation of ovotransferrin and ovalbumin from a gel permeation chromatographic peak. The purities were estimated as ca. 80, 100, 80 and 100% for ovomucin, lysozyme, ovotransferrin and ovalbumin, respectively. The purification yield was over 60% for each protein. Further characterization of purified lysozyme revealed that it was fully active and homogeneous in relation to the electrospray ionization mass spectrum. The electrospray ionization mass spectrum showed different ovotransferrin species. The amino acid composition of purified ovomucin was compared to those published previously.

Amino Acids↗

An inventory of mucin genes in the chicken genome shows that the mucin domain of Muc13 is encoded by multiple exons and that ovomucin is part of a locus of related gel-forming mucins.

BACKGROUND: Mucins are large glycoproteins that cover epithelial surfaces of the body. All mucins contain at least one PTS domain, a region rich in proline, threonine and serine. Mucins are also characterized by von Willebrand D (VWD) domains or SEA domains. We have developed computational methods to identify mucin genes and proteins based on these properties of the proteins. Using such methods we are able to characterize different organisms where genome sequence is available with respect to their mucin repertoire. RESULTS: We have here made a comprehensive analysis of potential mucins encoded by the chicken (Gallus gallus) genome. Three transmembrane mucins (Muc4, Muc13, and Muc16) and four gel-forming mucins (Muc6, Muc2, Muc5ac, and Muc5b) were identified. The gel-forming mucins are encoded within a locus similar to the corresponding human mucins. However, the chicken has an additional gene inserted between Muc2 and Muc5ac that encodes the the alpha-subunit of ovomucin, a protein similar to Muc2, but it is lacking a PTS domain. We also show that the beta-subunit of ovomucin is the orthologue of human MUC6. The transmembrane Muc13 gene is in chicken as well as in mammals adjacent to the HEG (heart of glass) gene. HEG has PTS, EGF and transmembrane domains like Muc13, suggesting that these two proteins are evolutionary related. Unlike previously known mucins, the PTS domain of Muc13 is encoded by multiple exons, where each exon encodes a repeat unit of the PTS domain. CONCLUSION: We report new mucin homologues in chicken and this information will aid in understanding the evolution of mucins in vertebrates. The fact that ovomucin, a protein not found in mammals, was located in the same locus as other gel-forming mucins provides strong support that these proteins are evolutionary related. Furthermore, a relationship of HEG and the transmembrane Muc13 is suggested on the basis of their biochemical properties and their presence in the same locus. Finally, our finding that the chicken Muc13 is distributed between multiple exons raises the interesting possibility that the length of the PTS domain could be controlled by alternative splicing.

Amino Acid Sequence↗

Glycopeptide derived from hen egg ovomucin has the ability to bind enterohemorrhagic Escherichia coli O157:H7.

Ovomucin glycopeptide (OGP) was prepared by size exclusion chromatography after Pronase digestion of hen egg ovomucin, and the binding of OGP to foodborne pathogens (Bacillus cereus,Clostridium perfringens, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enteritidis, Salmonella typhimurium, and Staphylococcus aureus) was investigaed. Binding assays with biotinylated bacteria as probes in microtiter plates showed that OGP bound to only E. coli O157:H7 among these foodborne pathogens. Periodate treatment markedly reduced the binding ability, indicating that E. coli O157:H7 bound to carbohydrate moieties of OGP. Lectin blot analysis with Maackia amurensis (MAA) and Sambucus nigra (SNA), which are specific for oligosaccharides containing sialic acid, revealed their binding sites in OGP were similar to the E. coli O157:H7 binding sites that were probed with biotinylated E. coli O157:H7 after Western blotting of OGP. Sialydase treatment of OGP abolished its ability to bind E. coli O157:H7, demonstrating that sialic acid played an important role in the binding. These results suggest that OGP has E. coli O157:H7-specific binding sites that consist of sialic acid. On the basis of these properties, OGP has the potential to be an ingredient with a protective effect against E. coli O157:H7 infection and to be a novel probe for the detection of E. coli O157:H7 in the food hygiene field.

Animals↗

Separation of ovomucin subunits by gel filtration: enhanced resolution of subunits by using a dual-column system.

An improved procedure involving a dual-column gel-filtration system for the separation of ovomucin subunits is described. Ovomucin, prepared from thick egg albumin by precipitation, was separated in the presence of sodium dodecyl sulfate (SDS) and beta-mercaptoethanol by using two Sephacryl S-400 HR gel-filtration columns connected in series. The separation resulted in the isolation of eight peaks. The amino acid compositions and SDS-polyacrylamide gradient gel electrophoretic pattern of each peak were determined.

Amino Acids↗

New allergens from hen's egg white and egg yolk. In vitro study of ovomucin, apovitellenin I and VI, and phosvitin.

Three hen egg yolk proteins, apovitellenins I and VI and phosvitin, and one egg white protein, ovomucin, were purified and tested for their ability to bind IgE in the sera of patients hypersensitive to egg. All of the proteins bound IgE from the sera of egg-allergic individuals in the radioallergosorbent test, and they also inhibited binding of IgE to the parent fractions-either egg yolk (apovitellenins I and VI and phosvitin) or egg white (ovomucin). It appears that apovitellenins I and VI are major allergens for some of the individuals tested. This is the first report of the in vitro allergenicity of these proteins.

Allergens↗

Activation of macrophages by sulfated glycopeptides in ovomucin, yolk membrane, and chalazae in chicken eggs.

Sulfated glycopeptides in ovomucin, chalazae and yolk membrane were found to activate cultured macrophage-like cells, J774.1, and TGC-induced macrophages from the peritoneal cavity of male mice. The macrophage-stimulating activity was estimated by the growth and morphology of the cells, H2O2 generation, and interleukin-1 (IL-1) production from the cells. The in vitro culture assay with macrophages showed that the protease digests of ovomucin, yolk membrane, and chalazae induced morphologic alteration and increased H2O2 generation and IL-1 production in lower concentration (100 micrograms/ml). The isolation of the components having macrophage-stimulating activity was attempted to elucidate the molecular mechanism. The O-linked carbohydrate chains, consisting of N-acetylgalactosamine, galactose, N-acetylneuraminic acid and sulfate, in the sulfated glycopeptide were identified as a component having macrophage-stimulating activity.

Animals↗

Egg ovomucin attenuates hypercholesterolemia in rats and inhibits cholesterol absorption in Caco-2 cells.

This experiment was designed to evaluate the effect of casein or ovomucin (OV) on the micellar solubility of cholesterol and the taurocholate binding capacity in vitro. We also evaluated the effects of casein or OV on cholesterol metabolism in rats and Caco-2 cells. OV had a significantly greater bile acid-binding capacity than that of casein in vitro. Micellar cholesterol solubility in vitro was significantly lower in the presence of OV compared to casein. The cholesterol micelles containing OV significantly suppressed cholesterol uptake by Caco-2 cells compared to the cholesterol micelles containing casein. Consistent with these in vitro findings, OV-feeding significantly increased the fecal excretion of bile acids or cholesterol compared with casein-feeding. Serum total cholesterol was significantly lower in rats fed OV than in those fed casein. The concentrations of total lipids in liver were significantly lower in the OV-fed group compared with the casein group. These results suggest that the suppression of cholesterol absorption by direct interaction between cholesterol mixed micelles and OV in the jejunal epithelia is part of the mechanism underlying the hypocholesterolemic action of OV. OV may also inhibit the reabsorption of bile acids in the ileum, thus lowering the serum cholesterol level.

Animals↗

1H and 13C-NMR assignments for sialylated oligosaccharide-alditols related to mucins. Study of thirteen components from hen ovomucin and swallow nest mucin.

Four hundred MHz 1H-NMR and 100 MHz 13C-NMR spectra of thirteen sialylated oligosaccharide-alditols isolated from hen ovomucin and swallow nests (Collocalia mucin) were studied. The resonance assignments were determined by combining multiple-relayed coherence-transfer chemical-shift-correlated spectroscopy (multiple-Relay-Cosy) and 1H/13C chemical-shift-correlated 2-D experiments.

Animals↗

Amino acid sequence of alpha-subunit in hen egg white ovomucin deduced from cloned cDNA.

The primary amino acid sequence of alpha-subunit in ovomucin (OVM) from hen thick egg white was determined. The 2087 amino acid residues with a relative molecular mass of 230.9 kDa along the full length of the alpha-subunit were represented. The alpha-subunit contains domains, arranged from the N- to C-terminals in the following order: D1-D2-D'-D3-R (central region)-D4-C1-CK (Cystine-knot), in a manner similar to the arrangement of D, C and CK domains in human pre-pro-von Willebrand factor (hpp-vWF) and hMUC2. The alpha-subunit showed identities on amino acid sequences with hpp-vWF and hMUC2 at 33 and 41% in the N-terminal region and 30 and 38% in the C-terminal region, respectively. The numbers and positions of cysteine residues were highly conserved among alpha-subunit, hpp-vWF and hMUC2. However, R showed no virtual sequence homology with the corresponding regions in two proteins. It was estimated that alpha-subunit was not part of a large peptide of OVM, but was independently synthesized from beta-subunit.

Amino Acid Sequence↗

Differences in hemagglutination inhibition activity against bovine rotavirus and hen Newcastle disease virus based on the subunits in hen egg white ovomucin.

The hemagglutination inhibition (HI) activity of ovomucin (OM) subunits, and the effects of alkylation before and after reduction and protease treatments on the HI activity of OM to bovine rotavirus (RV) and hen newcastle disease virus (NDV) were investigated. The appearance of the HI activity of Om against RV was accomplished by a macromolecule composed of alpha- and beta-subunits, while that against NDV required the beta-subunit moiety only.

Alkylation↗

Complete 1H- and 13C-n.m.r. assignments for two sulphated oligosaccharide alditols of hen ovomucin.

The complete 1H- and 13C-n.m.r. assignments for beta-D-Galp-(1----4)-beta-D-GlcpNAc-6-SO3H-(1----6)-[beta-D-Galp-(1----3 )]- D-GalNAcol and alpha-NeuAcp-(2----3)-beta-D-Galp-(1----3)-[beta-D-Galp-(1----4)-b eta-D- GlcpNAc-6-SO3H-(1----6)]-D-GalNAcol were made by a combination of 2-D correlation experiments (Relayed-Cosy; and 13C,1H Correlation-shift n.m.r. spectroscopy), and 1-D n.m.r. spectroscopy. The results illustrate the ability of these methods to locate sulphate and NeuAc groups in anionic mucinous glycoproteins.

Animals↗