Structural glycoprotein from the media of pig aorta. Aggregation of the S-carboxamidomethyl subunits

3H-mannose utilization by fibroblasts of the periodontal ligament

The synthesis, intracellular translocation, and secretion of mannose-containing glycoproteins(s) by periodontal ligament fibroblasts have been investigated by means of electron microscopic radioautography. Tritiated mannose was administered to young mice via jugular vein, and radioautographs were prepared at 5, 10, 20, and 35 minutes, 4 and 8 hours after injection. Analysis of electron microscopic radioautographs revealed a maximum labeling (94%) with 3H-mannose of the rough endoplasmic reticulum at 5 minutes. Labeling of the Golgi components started to increase from 10 minutes (14%) and reached a maximum level at 20 minutes (31.2%). At 35 minutes, secretion granules, dense bodies, profiles of intracellular collagen, and the cell surface were labeled. At 8 hours, most labelling (79.2%) was extracellular, and associated either with the collagenous matrix (43.7%) or the cell surface (35.5%). Cytoplasmic vesicles containing dense materials around collagen fibrils were also labeled at 8 hours. It is concluded that mannose is directly incorporated into the rough endoplasmic reticulum (RER), and that mannose-containing glycoprotein(s) are packaged in the Golgi apparatus into secretory granules. Mannose-containing glycoprotein(s) become distributed on the periodontal ligament (PDL) fibroblast cell surface, cytoplasmic dense bodies, and the extracellular matrix.

Fibrillar structure of alpha-elastin methylester complexes with glycoproteins and proteoglycans

alpha-Elastin methylester forms with proteoglycan subunits and structural glycoproteins water-insoluble complexes which after staining with phosphotungstic acid (pH 7.0), reveal at large magnification bundles of slender smooth fibrils with a diameter from 4 to 5 nm. Similar fibrils can be observed after interaction of alpha-elastin methylester with chondroitin sulfate, but only if fixation with glutaraldehyde is used prior to staining. Phosphotungstic acid alters the organization of the complexes, in particular those formed with ligands of low molecular weight. The possible biological significance of the interactions studied is discussed.

Structural glycoproteins from rabbit aortic media

Rabbit aortic intima-media fragments were incubated with [14C]mannose and [3H]fucose for 6 h to detect glycoproteins synthesized in situ. The radioactively labelled and the non-labelled samples were extracted with 0.2 mM-CaCl2/0.5 mM-dithiothreitol/0.5 mM-ATP and chloroform/methanol/water (4:4:1, by vol.). The delipidated residue was extracted with 5 M-guanidinium chloride/0.05 M-dithiothreitol/0.1 M-Tris/0.4% Na2EDTA, pH 7.5, before (extract 1) and after hydrolysis with collagenase (extract 2). The proteins in extracts 1 and 2 were S-carboxamidomethylated and separated by molecular-sieve chromatography, polyacrylamide-gel electrophoresis and isoelectric focusing in sucrose gradients in urea. The apparent molecular weights of glycoproteins were 36 000 (glycoprotein I) from extract 1, 50 000 (glycoprotein II) and 130 000 (glycoprotein III) from extract 2. The molecular weights of the non-labelled and radioactively labelled glycoproteins were identical. Glycoproteins I, II and III contain large amounts of polar amino acids and methionine. They contain neither hydroxyproline nor 3-methylhistidine. A hydroxyproline-containing component of 160 000-apparent-mol.wt. relatively rich in polar amino acids and labelled with incorporated sugars was isolated from extract 1. The incorporation in vitro of radioactive sugars into glycoproteins I, II, III and collagenous glycoproteins indicates that they are synthesized in the surviving aorta by the smooth-muscle cells.

Evidence for a mechanical coupling of glycoprotein microfibrils with collagen fibrils in Wharton's jelly

Wharton's jelly of human umbilical cord is known to contain hyaluronic acid and sulphated glycosaminoglycans (probably as proteoglycans) immobilized in an insoluble collagen fibril network. A secondary, independent, insoluble network based on glycoprotein microfibrils of 13 nm diameter and interpenetrated with the collagen network has now been found in amounts corresponding to 9% of the weight of collagen. Elastin, however, is absent. Tissue slices placed in physiological buffer swell to two-fold their in vivo volume. This is due to the influence of the polysaccharides since treatment with either testicular hyaluronidase, Streptomyces hyaluronidase or chondroitinase ABC, causes their quantitative removal and abolishes the swelling tendency of tissue. Tissue so treated remains close to its in vivo volume indicating that for this state the fibrillar network, overall, is in its relaxed unstressed configuration. Subsequent treatment with a protease causes the degradation of the glycoprotein microfibril network and a two-fold increase in tissue volume while treatment with bacterial collagenase, resulting in the solubilization of 46% of the collagen, causes only a slight deswelling. These results suggest that the unstressed configuration of the network system at the in vivo volume of tissue is due to the collagen network being held in compression by the microfibril network. With intact tissue protease digestion with trypsin, in addition, causes a preferential release of sulphated glycosaminoglycans. Hyaluronic acid, however, remains largely immobilized.

Healing of biodegradable vascular prosthesis. Incorporation of 3H-valine into proteins in the subendothelial scar and host intima-media of rat aorta

Heparin treated and aldehyde crosslinked rat aorta segments were implanted in infrarenal aorta of homologous rats. One year following aortic replacement, the subendothelial scar and the prosthetic remnants were excised. The scar and the host intima-media were incubated with 3H-valine for 4 h and extracted with 5 M guanidinium chloride--0.05 M dithiothreitol--0.1 M Tris--0.1% EDTANa2 at pH 7.5 prior (Extract 1) and following (Extract 2) hydrolysis of collagen. The radioactivity of extract 1 accounted for approximately 80% of the total label incorporated in the scar and host intima-media. The 3H-label of extract 1 adjusted for the tissue collagen content was about twenty times higher in the scar than in the host aorta. The major 3H protein peaks from Extract 1 of scar and host aorta were of 130 K, 100 K and 70 K apparent molecular weight, based on polyacrylamide gel electrophoresis in SDS. Hydrolysis with 2N KOH of the extraction residue from the host aorta and scar yielded 3H-val-pro dipeptides and hydrolysis with 6N HCl desmosines. The incorporation pattern of 3H-valine into proteins and the presence of elastin synthesized de novo in the scar replacing the prosthesis indicate macromolecular repair of the host aortic wall.

Isolation and characterization of lung connective-tissue glycoproteins

1. Glycoproteins of hamster, rat and baboon lung parenchyma were investigated by using [14C]glucosamine incorporation in vitro followed by sequential extraction of the macromolecular components and characterization of the glycoproteins in the extracts. 2. Slices of lung parenchyma maintained in vitro incorporated [U-14C]glucosamine linearly with time into non-diffusible macromolecules for up to 5h. All the macromolecule-associated 14C label was present as [14C]glucosamine. 3. These 14C-labelled macromolecules were extracted from previously delipidated and salt-extracted lung by 5M-guanidinium chloride in the presence of dithiothreitol and proteinase inhibitors before (extract A1) and after (extract A2) hydrolysis of the collagen by collagenase. The [14C]glucosamine-labelled glycoproteins in extracts A1 and A2 contained 55 and 5% respectively of the total [14C]glucosamine incorporated in the lung of all three species studied. 4. The [14C]glucosamine-labelled glycoproteins were analysed by gel-filtration chromatography, sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and isoelectric focusing. The major [14C]glucosamine-labelled glycoproteins of baboon lung parenchyma had apparent mol.wts. of about 400 000, 140 000 and 65 000 with isoelectric points respectively of 4.8, 5.4 and 5.4. The hamster lung glycoproteins with isoelectric points of 4.1 and 5.8 were devoid of hydroxyproline and contained galactose, mannose and N-acetylglucosamine. These experiments indicate that several distinct glycoproteins are synthesized in situ by the cells of pulmonary parenchyma and may well play a role in its structure and function.

Immunological studies with human aortic elastin

Antibodies to human fetal aortic elastin were isolated from sheep immunized with alpha-elastin peptides. In preliminary tests of specificity using passive hemagglutination, partial cross-reactivity was demonstrated with alpha-elastin from other species. However, in a double antibody radio-immunoassay alpha-elastin peptides from other mammalian species failed to compete with 125I-labelled human alpha elastin. These results suggest the existence of at least two different antigenic sites on the elastin molecule. One, a high affinity site, demonstrates species specificity at low antigen/antibody concentrations. The other, a low affinity site, is common to mammalian elastins and is demonstrated at high antibody/antigen concentrations. In the radioimmunoassay the antibodies showed considerably less avidity for adult human alpha-elastin than for the fetal antigen. This implies that the species specific site is age-dependent and probably involves the cross-linking region of the elastin molecule. Using the sheep antiserum immunohistochemical staining of elastic tissue has been developed. This should prove to be a useful technique for studying polymeric elastin in intact tissue by light microscopy and at the ultrastructural level.

Characterization of a structural glycoprotein from bovine ligamentum nuchae exhibiting dual amine oxidase activity

A structural glycoprotein has been extracted from bovine ligamentum nuchae by using 5 M guanidine hydrochloride containing a disulfide bond reducing agent and purified by preparative gel electrophoresis. The isolated material appeared to be monodisperse, with a molecular weight of approximately 34000, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by analytical ultracentrifugation. It contains 10% carbohydrate comprising mannose, N-acetylglucosamine, galactose, and sialic acid in a 6:5:3:3 molar ratio. The glycoprotein has been assayed for peptidyl-lysine oxidase activity by using [3H]lysine-aortic elastin, prepared from 15- to 17-day-old chick embryos, as a substrate. In the absence of free lysine, the specific activity of the preparation over a 2-h incubation was approximately 60 X 10(4) dpm/mg of purified protein. Addition of 10 mM lysine resulted in an approximately 50% decrease in the specific activity. Free lysine was shown to act as a substrate for the glycoprotein preparation as indicated by control experiments using [3H]lysine in place of the aortic substrate. These results demonstrate that the glycoprotein exhibits a dual amine oxidase activity. In the presence of 0.27 mM beta-aminopropionitrile fumarate, a concentration which completely inhibits peptidyl-lysine oxidase activity in other lysyl oxidases, the glycoprotein preparation was inhibited by approximately 14%. In the absence of 5 M guanidine hydrochloride and reducing agent, the glycoprotein undergoes aggregation which in the presences of copper ions results in the formation of cylindrical tactoids, the diameter of which (11 nm) corresponds closely to that of the fibrils which in the majority of connective tissue matrices constitute the microfibrillar component mainly associated with elastic fibers.

The microfibrillar components of porcine lung elastic fiber

Lung elastic fiber was isolated from anatomically defined porcine parenchymal tissue. Constituent microfibrillar acidic structural glycoproteins (external and meso) were obtained by mild dissociative quantitative procedures, leaving the elastin-rich fraction as the insoluble residue. The presumptive cross-link lysylnorleucine was identified in both of the highly aggregated acidic structural glycoprotein fractions. The external-acidic structural glycoproteins require dithiothreitol but not sodium dodecyl sulfate for solubility. Both sodium dodecyl sulfate and dithiothreitol at 55 degrees C are required to release meso-acidic structural glycoproteins from the elastic fiber. On the basis of physical characteristics, I propose a new fraction from elastic fiber, the meso-acidic structural glycoprotein. The meso-acidic structural glycoproteins may have been in longest and closest contact with the elastin core of the elastic fiber. Alkali-soluble peptides from the elastin-rich fraction contained desmosine and high concentrations of hydroxyproline, polar amino acids and lysylnorleucine. The cross-link, lysylnorleucine, may be evidence of covalent bonding of glycoprotein to elastin, explaining my inability to obtain the biopolymer elastin with the composition of tropoelastin corrected for the desmosine-lysine content.

Interaction of a tropoelastin model with connective tissue components

It has been suggested that tropoelastin interacts with macromolecular components of connective tissue during the formation of elastic fibers. alpha-Elastin, used traditionally as a model of tropoelastin and mature elastin, is not suitable for the monitoring of this interaction in vitro. Therefore a new model of tropoelastin, the methyl ester of alpha-elastin, was synthesized and the interaction of this modified elastin with hyaluronic acid, chondroitin sulfate, proteoglycan subunits, solubilized structural glycoproteins and collagen was studied by turbidimetric measurement. Results indicate that alpha-elastin methyl ester is a better model of tropoelastin than alpha-elastin especially in those experiments where ionic interactions are believed to occur. It was also found that alpha-elastin methyl ester formed aggregates with hyaluronic acid, chondroitin sulfate, proteoglycan subunits and solubilized structural glycoproteins at room temperature and under conditions close to physiological ones. Alpha-elastin does not interact with these compounds under similar conditions. The character of the bonds involved in the interaction and the possible biological significance of the experiments are discussed.

Studies on the assembly of the rat lens capsule. Biosynthesis of a cross-linked collagenous component of high molecular weight

1. Intact rat lenses in tissue culture synthesize hydroxy[3H]proline-containing polypeptides of apparent mol.wt. approx. 180000, which become assembled into aggregates of higher molecular weight with time. 2. Both the 180000-mol.wt. species and the aggregates are components of the deoxycholate-insoluble base-membrane matrix. 3. Formation of the high-molecular-weight aggregate is accompanied by the biosynthesis of the reducible hydroxylysine-derived cross-link hydroxylysino-5-oxo-norleucine. 4. Hydroxylysino-5-oxonorleucine and dehydrohydroxylysinonorleucine are the major reducible cross-links present in intact foetal and 1-month-old calf lens capsules.

Structural glycoprotein, fact or artefact

It has been repeatedly claimed that structural glycoprotein or SGP is a major component of many connective tissues, particularly aorta. SGP is usually defined as material extractable from tissue with chaotropic agents such as urea and having an amino acid composition matching that of other, similar extracts. It has been claimed that SGP comprises 10-60% of the dry weight of aortic tissue. This paper describes a study in which aorta was exhaustively extracted with agents previously claimed to extract SGP. All the extracts yielded mixtures of proteins which, upon separation by polyacrylamide gel electrophoresis, were found to consist largely of actin, collagen, myosin and other known proteins. No significant quantity of any one unidentified protein was found which could have been SGP. This study casts grave doubt upon the existence of SGP as a major component of aorta.

Association of structural glycoproteins with lipids or lipoproteins

Gradient density ultracentrifugation was used to assess the lipid binding of 125I-labelled structural glycoproteins and standard proteins. The results show that solubilized structural glycoproteins from cartilage or aorta will associate spontaneously with lipids or lipoproteins. In addition, structural glycoprotein preparations from tissues which have not been delipidated contain a fraction which is already associated with lipid. Standard proteins do not behave in the same way. It is proposed that structural glycoprotein-lipid binding may be one of the mechanisms involved in the intercellular deposition of plasma lipoproteins in atherosclerotic arteries.