Isolation of a laminin-binding protein from muscle cell membranes

Skeletal muscle myofibers are each ensheathed by a continuous basal lamina consisting predominantly of type IV collagen, laminin and heparan sulfate proteoglycan. In order to identify laminin-binding components in the muscle cell surface, plasma membranes from mouse thigh muscle and from rat L6 myoblasts were separated by polyacrylamide gel electrophoresis and transferred to nitrocellulose paper by electroblotting. Incubation of the transferred samples with ¹²⁵I-labelled laminin revealed a prominent band of approximate mol. wt. 68 000. A protein of this mol. wt. was isolated by affinity chromatography of muscle cell plasma membranes on laminin-Sepharose. The hydrophobic protein has an apparent mol. wt. of 68 000 and has a high content of serine, glycine and acidic amino acids. After detergent solubilization the purified protein binds to laminin-coated Sepharose beads at a higher rate than to beads coated with either fibronectin or collagen types I and IV. The interaction of the protein, called LB 68, with laminin was also studied after incorporation into synthetic lecithin vesicles. While detergent-solubilized LB 68 bound to ¹²⁵I-labeled laminin only at lower than physiological ionic strength, liposome-incorporated LB 68 bound to laminin in the absence of detergents under physiological conditions. We propose that this protein is involved in the interaction of myoblasts with laminin substrates and thus may participate in the anchorage of the basal lamina in the plasmalemma of myotubes.     

Isolation and characterisation of arthropod gap junctions

Gap junctions have been isolated from the hepatopancreas of the crustacean arthropod, Nephrops norvegicus (Norway lobster). SDS-PAGE of these preparations shows two major protein bands, mol. wt. 18 000 (18 K) and mol. wt. 28 000 (28 K). The 18-K and 28-K proteins are interconvertible, cannot be distinguished by two dimensional tryptic and chymotryptic peptide mapping, and therefore appear to be different (most likely monomeric and dimeric) forms of the same protein. The protein can also aggregate to higher multimeric forms mol. wt. 38 000 (presumed trimer), and mol. wt. 52 000 (presumed tetramer). The buoyant density of the isolated gap junctions in continuous potassium iodide gradients is 1.260 g/cm³. The junctions are progressively solubilized in increasing SDS concentrations, mostly between 0.1% and 0.2% SDS, and this is accompanied by the release of the 18-K and 28-K forms of the junctional protein. The Nephrops hepatopancreas 18-K junctional protein has antigenic determinants in common with the vertebrate 16-K junctional protein as shown by cross-reactivity with two different affinity purified antibody preparations. However, no detectable similarity can be seen between the major ¹²⁵I-labelled tryptic and chymotrytpic peptides of the Nephrops hepatopancreas 18-K protein and the mouse liver 16-K protein.     

Release of Paramecium immobilization antigen to the non-nutrient medium

The instability of Paramecium aurelia surface components has been shown: after 60 min incubation of dense cell suspension (1–2 · 10⁶ cells per ml) in Tris-Ca buffer at 4 °C or 23 °C the surface coat was partially stripped off and the proteins were released to the medium. The electrophoretic analysis of the released proteins shows one major band of mol. wt. 280 000–300 000 and some minor bands. The major released protein is the immobilization antigen as proved using immunodiffusion test and antibody precipitation technique.     

A nerve terminal anchorage protein from electric organ

The nerve terminal and the postsynaptic receptor-containing membranes of the electric organ are both linked to the basal lamina that runs between them. We have identified an extracellular matrix protein whose physical properties suggest it anchors the nerve terminal to the basal lamina. The protein was identified because it shares an epitope with a proteoglycan component of electric organ synaptic vesicles. It too behaves like a proteoglycan. It is solubilized with difficulty from extracellular matrix fractions, elutes from DEAE Sephacel at pH 4.9 only at high ionic strength, and binds to a laminin affinity column from which it can be eluted with heparin. Under denaturing conditions it sediments rapidly and has a large excluded volume although it can be included in Sephacryl S-1000 columns. This large, highly charged extracellular matrix molecule can be readily reconstituted into liposomes consistent with the presence of a hydrophobic tail. By immunoelectron microscopy the antigen is found both in synaptic vesicles and on the plasma membrane of the nerve terminal. Since this is the first protein described that links the nerve terminal membrane to the extracellular matrix, we propose calling it terminal anchorage protein one (TAP-1).     

Autoantibodies to ribonucleoprotein particles containing U2 small nuclear RNA.

Autoantibodies exclusively precipitating U1 and U2 small nuclear ribonucleoprotein (snRNP) particles [anti-(U1,U2)RNP] were detected in sera from four patients with autoimmune disorders. When tested by immunoblotting, these sera recognized up to four different protein antigens in purified mixtures of U1-U6 RNP particles. With purified antibody fractions eluted from individual antigen bands on nitrocellulose blots, each anti-(U1,U2)RNP serum precipitated U2 RNP by virtue of the recognition of a U2 RNP-specific B" antigen (mol. wt. 28 500). Antibodies to the U2 RNP-specific A' protein (mol. wt. 31 000) were found in only one serum. The B" antigen differs slightly in mol. wt. from the U1-U6 RNA-associated B/B' antigens and can be separated from this doublet by two-dimensional gel electrophoresis, due to its more acidic pI. In immunoprecipitation assays, the purified anti-B" antibody specificity also reacts with U1 RNPs which is due to cross-reactivity of the antibody with the U1 RNA-specific A protein, as demonstrated by immunoblotting using proteins from isolated U1 RNPs as antigenic material. Thus the A antigen not only bears unique antigenic sites for anti-A antibodies contained in anti-(U1)RNP sera, it also shares epitopes with the U2 RNP-specific B" antigen.     

Monoclonal antibody purification by affinity chromatography with ligands derived from the screening of peptide combinatory libraries

The peptide, Ala-Pro-Ala-Arg (APAR), was selected from the screening of a tetrapeptide combinatorial synthetic library as the ligand for affinity purification of an anti-Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF) monoclonal antibody (Mab) developed in mouse ascitis. The affinity chromatographic matrix obtained by attachment of APAR to agarose, having a peptide density of 0.5 mol ml^–1, showed a maximum capacity of 9.1 mg Mab ml^–1 and a dynamic capacity of 3.9 mg Mab ml^–1. A 95% yield of electrophoretically pure anti-GM-CSF was obtained in a single step.     

Biosynthesis and molecular nature of the T3 antigen of human T lymphocytes

Immunoprecipitates of the T3 antigen prepared from HPB-ALL cells by using the monoclonal antibody UCH-T1 were analysed by SDS-polyacrylamide gel electrophoresis. Cells which had been biosynthetically labelled for up to 4 h gave a major polypeptide of mol. wt. 19 000 plus two weaker, more diffuse bands of mol. wts. 21 000 and 23 000, whereas surface labelled cells gave a prominent band of mol. wt. 19 000, a major band of 21 000 and a weaker diffuse band of approximately 26 000. As judged from their sensitivity to proteinase-K digestion, all the above polypeptides possess a transmembrane orientation. Digestion with endoglycosidases H and F (endo-H and endo-F), and tunicamycin treatment indicate that all the polypeptides, except that of 19 000 mol. wt. are N-glycosylated. The 21 000 and 23 000 mol. wt. chains possess both immature and mature oligosaccharide units, whereas the 26 000 mol. wt. band apparently has mature units only. Pulse chase experiments combined with digestion by endo-F and endo-H suggest that the N-glycosylated polypeptides are derived from two polypeptides of mol. wts. 14 000 and 16 000. It is concluded that the T3 antigen is derived from three different non-glycosylated polypeptides two of which are subsequently N-glycosylated to give the 21 000, 23 000 and 26 000 forms. The cell surface T3 antigen most probably comprises at least two distinct, non-covalently associated polypeptides, but the number and types of polypeptides giving rise to the whole molecule and whether different complexes exist is at present unclear.     

Identification of a specialized extracellular matrix component in Drosophila imaginal discs

We have generated a monoclonal antibody that recognizes a major component of a specialized extracellular matrix in Drosophila imaginal discs. In mature larvae, antibody binding is observed almost exclusively on imaginal discs. On the basal surface of the thoracic discs, the antigen is localized to particular regions of the epithelium, and ultrastructural studies indicate that the antigen is found in a fibrous network secreted between the cells and the basal lamina. The localized expression indicates that the matrix is not simply related to disc differentiation, as all regions of the columnar disc epithelium are determined to secrete adult cuticle. A correlation of the antigen distribution with known developmental events leads us to propose that the antigen-containing network provides an extensible matrix for the rapid elongation of the disc epithelium during evagination; consistent with this, the antigen is a component of the matrix between the dorsal and ventral surfaces of the evaginated wing pouch. The antigen is very large (greater than 5 X 10(5) Da), can be labeled metabolically with methionine and sulfate, and is digested by chondroitinase ABC; these biochemical characteristics indicate that the antigen is a proteoglycan.     

Electron transport systems of Candida utilis. Purification and properties of the respiratory chain-linked external NADH dehydrogenase+

The respiratory chain-linked external NADH dehydrogenase has been isolated from Candida utilis in highly purified form. The enzyme is soluble and has a molecular weight of approx. 1.5 · 10⁶. The enzyme contains two moles of FMN per mole of enzyme and is composed of two large subunits of mol. wt. 270 000 and eight smaller subunits of mol. wt. 135 000. Iron and copper are present in the preparations, but appear to be contaminants. The enzyme catalyzes the oxidation of NADH and NADPH at nearly equal rates and reacts readily with 2,6-dichlorophenolindophenol, CoQ₆ and CoQ₁ derivatives as acceptors. Rotenone (10^?5 M) and seconal (10^?3 M) do not inhibit enzymatic activity.     

The interrelations between high- and low-molecular-weight forms of normal and mutant (Krabbe-disease) galactocerebrosidase

Galactocerebrosidase (β-d-galactosyl-N-acylsphingosine galactohydrolase; EC 3.2.1.46) activity of brain and liver preparations from normal individuals and patients with Krabbe disease (globoid-cell leukodystrophy) have been separated by gel filtration into four different molecular-weight forms. The apparent mol.wts. were 760000±34000 and 121000±10000 for the high- and low-molecular-weight forms (peaks I and IV respectively) and 499000±22000 (mean±s.d.) and 256000±12000 for the intermediate forms (peaks II and III respectively). On examination by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the high- and low-molecular-weight forms revealed a single protein band with a similar mobility corresponding to a mol.wt. of about 125000. Antigenic identity was demonstrated between the various molecular-weight forms of the normal and the mutant galactocerebrosidases by using antisera against either the high- or the low-molecular-weight enzymes. The high-molecular-weight form of galactocerebrosidase was found to possess higher specific activity toward natural substrates when compared with the low-molecular-weight form. It is suggested that the high-molecular-weight enzyme is the active form in vivo and an aggregation process that proceeds from a monomer (mol.wt. approx. 125000) to a dimer (mol.wt. approx. 250000) and from the dimer to either a tetramer (mol.wt. approx. 500000) or a hexamer (mol.wt. approx. 750000) takes place in normal as well as in Krabbe-disease tissues.     

Protein composition and structure of human placental microvillous membrane. External surface, sialic acid containing, extrinsic and intrinsic components.

The microvillous membrane of human placenta is in direct contact with maternal blood and thus plays a vital role in many essential functions of the placenta. As an initial step in understanding the membrane proteins, and their relationship to these functions and to the structure of the membrane, we have investigated an isolated membrane preparation. Ten major peptide bands and an approximately equal number of minor bands were seen with sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Sialoglycoproteins were labeled with periodate (PA-³H) borohydride and external surface components with lactoperoxidase-[¹²⁵I] (LP-¹²⁵I). One principal (69 000 mol. wt) and several minor (100 000, 45 000, and 38–40 000 mol. wt) bands were labeled as Sialoglycoproteins and found to be exposed on the surface of the membrane. Approx. 50% of the membrane protein and all of the sialic acid was tightly bound to membrane lipid and resistant to extraction with dimethyl maleic anhydride (DMMA). Electron microscopy demonstrated extraction by DMMA of microfilaments presumptively identified as actin and other electron dense components from the villous core. The extracted supernate and the residual pellet differed markedly in protein composition. The supernatant contained bands of 180 000, 115 000, 85 000, 70–72 000, 45 000, and 38–40 000 mol. wt whereas the lipid pellet contained components of 200 000, 150 000, 100 000, 69 000, and 64 000 mol. wt. The lipid matrix with which these proteins were associated contained phosphatidyl choline and sphingomyelin and was similar in composition to other plasma membranes. Thus by using a variety of experimental approaches the proteins of the human placental microvillous membrane can be divided into groups based on their sialic acid content, exposure on the external surface, tightness of binding to the membrane lipid, and relation to membrane structure.     

Biological and biochemical properties of an isolate of cherry rasp leaf virus from red raspberry

A mechanically transmissible virus obtained from symptomless plants of a red raspberry selection imported into Scotland from Quebec, Canada was indistinguishable serologically from a cherry isolate of cherry rasp leaf virus (CRLV). The raspberry isolate, CRLV-R, was graft transmitted to several virus indicator species and cultivars of Rubus without inducing noticeable symptoms. In Chenopodium quinoa sap, CRLV-R lost infectivity after dilution to 10^-5 or heating for 10 min at 60°C but was infective after 16 days (the longest period tested) at 18°, 4° or - 15°C. The virus particles are isometric, c. 28 nm in diameter, and were purified with difficulty from infected C. murale and C. quinoa plants. The particles comprise two nucleoprotein components with sedimentation coefficients of 89 and 115 S and are prone to aggregate during purification. When centrifuged to equilibrium in CS₂SO₄ solution, purified virus preparations formed two major components with p= 1·28 and 1·36 g/cm³. Virus particles contained two RNA species which, when denatured in glyoxal and electrophoresed in agarose gels, had estimated mol. wt of 2·56 × 10⁶ (RNA-1) and 1·26 × 10⁶ (RNA–2). Infectivity of CRLV-R RNA was abolished by treatment with proteinase K, suggesting that the RNA is linked to protein necessary for infectivity; RNA molecules contained polyadenylate. In reticulocyte lysates, CRLV-R RNA stimulated the incorporation of ³H-leucine, mainly into two polypeptides of estimated mol. wt 200 000 and 102 000. When electrophoresed in polyacrylamide gels, protein obtained from CRLV-R particles purified by centrifugation to equilibrium in Cs₂SO₄ separated into three bands with estimated mol. wt 26 000 , 23 000 and 21 000.     

Arterial chondroitin sulfate proteoglycan: localization with a monoclonal antibody

We generated a monoclonal antibody (Mab) against a large chondroitin sulfate proteoglycan (CSPG) isolated from bovine aorta. This Mab (941) immunoprecipitates a CSPG synthesized by cultured monkey arterial smooth muscle cells. The immunoprecipitated CSPG is totally susceptible to chondroitinase ABC digestion and possesses a core glycoprotein of Mr approximately 400-500 KD. By use of immunofluorescence light microscopy and immunogold electron microscopy, the PG recognized by this Mab was shown to be deposited in the extracellular matrix of monkey arterial smooth muscle cell cultures in clusters which were not part of other fibrous matrix components and not associated with the cell's plasma membrane. With similar immunolocalization techniques, the CSPG antigen was found enriched in the intima and present in the medial portions of normal blood vessels, as well as in the interstitial matrix of thickened intimal lesions of atherosclerotic vessels. Immunoelectron microscopy revealed that this CSPG was confined principally to the space within the extracellular matrix not occupied by other matrix components, such as collagen and elastic fibers. These results indicate that this particular proteoglycan has a specific but restricted distribution in the extracellular matrix of arterial tissue.     

A major heat-shock protein defined by a monoclonal antibody.

A monoclonal antibody reacts with a polypeptide of 68 000 mol. wt. (p68) that accumulates to high levels during heat shock. The intracellular distribution of this antigen in normal and heat-shocked cells has been studied. It is a major component of non-stressed cells, where it is located predominantly in the cytoplasm, but also occurs in the nucleus. The nuclear accumulation is growth regulated, in that exponentially growing cells have strong nuclear immunofluorescence and confluent cells little. It is concentrated at the leading edge of motile fibroblasts and co-distributes with actin-containing microfilaments. Heat shock causes cytoplasmic and nuclear accumulation and there is new deposition in the periphery of cells. In normal cells the antigen in the nucleus is located in the nuclear lamina and matrix which increases during heat shock. The distribution of this molecule and the structures with which it interacts suggests that it is important in mediating the effects of heat shock.     

Cytoskeletal proteins of the cell surface in Tetrahymena : I. Identification and localization of major proteins

Isolated pellicles (cell ‘ghosts’) have been prepared from Tetrahymena thermophila strain B by two different methods. Using differential solubilization in combination with polyacrylamide gel electrophoresis and electron microscopy, we have tentatively identified the major proteins found in the surface-associated cytoskeleton. The ‘epiplasm’, a continuous layer of fibrous material found just beneath the surface membranes, appears to contain two major proteins. The smaller of the two (mol. wt 122 000 D) is believed to be present throughout the layer, whereas the larger protein (mol. wt 145 000 D) appears to be localized in the regions where ciliary basal bodies connect to the epiplasmic layer and to surface membranes. Evidence is presented which suggests that actin may also be present in this structure. Tubulin has been isolated from the cytosol of Tetrahymena and compared with cytoskeletal tubulin and porcine brain tubulin. A major protein of mol. wt 250 000 D which is found in Tetrahymena pellicles appears to be the major component of kinetodesmal fibers (striated elements which attach to the ciliary basal bodies).     

Olive latent ringspot virus, a newly recognised virus infecting olive in Italy

A manually transmissible virus, for which the name olive latent ringspot virus (OLRV) is proposed, was isolated from a symptomless olive tree. The virus was mechanically transmitted to test plants. Purified preparations of OLRV contained three classes of isometric particle, c. 28 nm in diameter, with sedimentation coefficients of 525 (T), 975 (M) and 1325 (B) and containing 0, 30 and 43% nucleic acid respectively. At equilibrium in CsCl gradients, the buoyant densities of T and M components were 1–29 and 1–43 g/cm³ respectively, whereas B component separated into two sub-components with buoyant densities of 1–51 g/cm³ (BJ and 1–52 g/cm³ (B₂). Particle preparations contained two species of single-stranded RNA with mol. wt 1–40 times 10⁶ and 2–65 times 10⁶, both necessary for infectivity. The coat protein of OLRV, dissociated under strong denaturing conditions, separated into four components in polyacrylamide gel electrophoresis. Over 75% of the protein was found in a band with mol. wt 57 600, but all four components were recognised as oligomers of a monomeric form with mol. wt 14 300. OLRV was serologically unrelated to 26 different isometric plant viruses including 17 recognised nepoviruses. Its properties strongly indicate that it is a hitherto undescribed member of the nepovirus group.     

Characterization of the SS-B (La) antigen in adenovirus-infected and uninfected HeLa cells.

The molecular composition and subcellular localization of the antigens recognized by anti-SS-B (La or Ha) antibodies was investigated. Ten anti-SS-B sera were selected by indirect immunofluorescence and by their immunological identity in counter-immunoelectrophoresis (CIE) with an anti-SS-B reference serum. All sera precipitated virus-associated (VA) RNA from cellular extracts of adenovirus-infected HeLa cells. Earlier results had shown that in adenovirus-infected HeLa cells a cellular 50 000 mol. wt. protein was tightly associated with VA RNA in situ. Our present results indicate that this 50 000 protein is the only SS-B antigen present in adenovirus-infected as well as in uninfected cells. A major part (greater than 80%) of the SS-B antigen is present in a readily extractable, soluble form. The rest is found in an insoluble form tightly associated with an internal nuclear structure that is mostly referred to as the nuclear matrix. Both forms are very susceptible to proteolytic degradation resulting in at least two distinct breakdown products of mol. wts. 40 000 and 25 000. The cellular 50 000 polypeptide is present in extracts of various types of cells and tissues, indicating that this antigen is very well conserved during evolution. The association of the 50 000 mol. wt. antigen with host- as well as viral-coded RNA polymerase III products also suggests an important function for this protein in the metabolism of these small RNAs.     

Distribution of the cell substratum attachment (CSAT) antigen on myogenic and fibroblastic cells in culture

Previous studies (Neff et al., 1982, J. Cell. Biol. 95:654-666; Decker et al., 1984. J. Cell. Biol. 99:1388-1404) have described a monoclonal antibody (CSAT Mab) directed against a complex of three integral membrane glycoproteins of 120,000-160,000 mol wt (CSAT antigen [ag]) involved in the cell matrix adhesion of myoblasts and fibroblasts. In localization studies on fibroblasts presented here, CSAT ag has a discrete, well-organized distribution pattern. It co-aligns with portions of stress fibers and is enriched at the periphery of, but not directly beneath vinculin-rich focal contacts. In this last location, it co-distributes with fibronectin, consistent with the suggestion that the CSAT ag participates in the mechanism by which fibroblasts attach to fibronectin. In prefusion myoblasts, which are rapidly detached by CSAT Mab, CSAT ag is distributed diffusely as are vinculin, laminin, and fibronectin. After fusion, myotubes become more difficult to detach with CSAT Mab. The CSAT ag and vinculin are organized in a much more discrete pattern on the myotube surface, becoming enriched at microfilament bundle termini and in lateral lamellae which appear to attach myotubes to the substratum. These results suggest that the organization of CSAT ag-adhesive complexes on the surface of myogenic cells can affect the stability of their adhesive contacts. We conclude from the sum of the studies presented that, in both myogenic and fibroblastic cells, the CSAT ag is localized in sites expected of a surface membrane mediator of cell adhesion to extracelluon of CSAT ag-adhesive complexes on the surface of myogenic cells can affect the stability of their adhesive contacts. We conclude from the sum of the studies presented that, in both myogenic and fibroblastic cells, the CSAT ag is localized in sites expected of a surface membrane mediator of cell adhesion to extracellular matrix. The results from studies that use fibroblasts in particular suggest the involvement of CSAT ag in the adhesion of these cells to fibronectin.     

Patterns of proteins synthesized by non-proliferating murine L cells

When L cells were plated at high density (2 × 10⁵/cm²), proliferation ceased within 3 days, but the cells remained viable and capable of reinitiating DNA synthesis for at least 16 days. SDS-polyacrylamide gel electrophoresis of [³⁵S]methionine labeled polypeptides at various intervals after plating revealed distinct changes in the relative abundance of major cellular proteins beginning 9 days after DNA synthesis ceased. An 84 000 mol. wt polypeptide increased markedly in amount while a polypeptide of 94 000 mol. wt disappeared. Autoradiograms following pulse-labeling showed that these changes were due to increased synthesis of the 84 000 mol. wt polypeptide and decreased synthesis of the 94 000 mol. wt polypeptide. Increased synthesis of a 109 000 mol. wt polypeptide occurred without a concomitant change in its relative abundance. These alterations in the pattern of proteins synthesized revert to normal after feeding with serum-free medium even though DNA synthesis does not resume. Therefore, it appears that even though no abrupt changes in the synthesis of major cellular proteins occurred upon cessation of proliferation, eventually a distinct adaptive pattern of protein synthesis develops in response to the changing culture conditions.