Deglycosylation of glycoproteins by trifluoromethanesulfonic acid

Transport and posttranslational processing of the vacuolar enzyme α-mannosidase in jack-bean cotyledons

α-Mannosidase (EC 3.2.1.24) is a vacuolar enzyme which occurs abundantly in the cotyledons of the jack-bean (Canavalia ensiformis (L.) DC). The mature enzyme is a tetramer with two polypeptides each of relative molecular mass (Mr) 66000 and Mr 44000. The enzyme has an interesting molecular structure because in its native form, it does not bind to concanavalin A (ConA) in spite of the presence of a high-mannose glycan. α-Mannosidase is synthesized in the developing cotyledons of jack-beans at the same time as the abundant proteins canavalin and ConA. The enzyme is synthesized as a precursor which has an Mr of 110000 and is associated with the endoplasmic reticulum (ER). Antibodies against the deglycosylated subunits cross-react with the Mr-110000 precursor. Processing of the precursor to the constituent polypeptides occurs posttranslationally, probably in the protein bodies. Immunocytochemical evidence shows that α-mannosidase is present in the ER and the Golgi complex of developing cells, and accumulates in the protein bodies.Labeling with [(3)H]glucosamine shows that after processing only the Mr-66000 polypeptide has glucosamine-containing glycans. The synthesis of these glycans is inhibited by tunicamycin, indicating that they are asparagine-linked oligosaccharides. Analysis of the glycans shows that there is a large glycan that is retained by ConA and a small glycan that is not retained by ConA. The large glycan is only partially sensitive to α-mannosidase because of the presence of a terminal glucose residue. Cross-reaction of the large subunit with an antiserum directed against small, complex glycans of plant glycoproteins indicates that this polypeptide probably has a xylose-containing glycan. Pulse-chase experiments carried out in the presence of tunicamycin show that the presence of glycans is not required for transport of α-mannosidase out of the ER-Golgi system.

Post-translational modification of the beta-subunit of the human fibronectin receptor

Monoclonal antibody DH12, directed against the beta-subunit of the fibronectin receptor recognizes a doublet of proteins (100 and 110 kDa) in Western blots of solubilized whole fibroblasts. Pulse-chase experiments with [35S]methionine in human skin fibroblasts suggested that the two proteins might be metabolically related as precursor (100 kDa) and product (110 kDa). Endo H digestion and [3H]fucose labeling suggested that maturation converted the high-mannose oligosaccharides (100 kDa) to the endoglycosidase H resistant complex type (110 kDa). This was supported by N-glycanase digestion and by chemical deglycosylation which showed a single polypeptide. Surface iodination of intact cells labeled only the presumed mature beta-subunit.

Purification and characterization of dihydropyridine receptor from rabbit skeletal muscle

Digitonin and 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propane sulfonate (Chapso) were used to solubilize the receptor of dihydropyridine calcium antagonists from the transverse tubule membranes of rabbit skeletal muscle. The receptor retained the ability for selective adsorption from either detergent extract by dihydropyridine-Sepharose. Incubation of the affinity resin with nitrendipine resulted in the elution of the receptor protein composed of two main polypeptides with molecular masses of 160 kDa and 53 kDa, as shown by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Only these two subunits were found in the receptor preparation purified to a specific dihydropyridine-binding activity of 2500-2800 pmol/mg protein (60-70% purity) from digitonin-solubilized membranes by a combination of wheat-germ-agglutinin--Sepharose, anion-exchange and dihydropyridine-Sepharose chromatography steps. The individual subunits were isolated in dodecyl-sulfate-denatured form from the preparation of the receptor, enriched by a two-step large-scale procedure applied to Chapso-solubilized membranes. The 160-kDa subunit slowly changed its apparent molecular mass to 125 kDa upon disulfide bond reduction without formation of novel peptides. This finding implies that 160-kDa subunit is cross-linked by intramolecular S-S bridge(s). Chemical deglycosylation with trifluoromethanesulfonic acid showed that the carbohydrate content of large and small subunits accounted for 7.5% and 6.6% by mass, respectively. The dihydropyridine receptor subunits are glycosylated through N-glycoside bonds only. In their ratio of polar to hydrophobic amino acid residues in the amino acid composition of the receptor subunits, these polypeptides behave rather as peripheral proteins. It is suggested that the main portion of polypeptide chains is located outside the membrane in contact with solvent.

Endogenous sugar-binding proteins in human breast tissue and benign and malignant breast lesions

Binding of carbohydrate moieties was detected in tissue sections of human breast by employing two types of labeled ligands: neoglycoproteins (chemically glycosylated, histochemically inert carrier protein) and desialylated naturally occurring glycoproteins. Paraffin-embedded, formalin-fixed sections from 40 benign and malignant breast lesions were examined for the presence and distribution of endogenous sugar receptors, employing a panel of 13 biotinylated neoglycoproteins, representing carbohydrates commonly found in naturally occurring glycoconjugates, and four biotinylated glycoproteins. Benign and malignant breast lesions revealed staining with mannosylated carrier neoglycoprotein in comparison to normal breast. A mixed pattern of staining localization and intensity was seen for different types of malignancy with this neoglycoprotein. Similarly, receptors for lactose and N-acetylglucosamine could only be detected within the cytoplasm for certain types of malignancy. Their nuclear localization, however, could also be seen in normal breast specimens. The extent of staining with different glycoproteins, containing different types of galactoside-terminal sugar chains, also appeared to differ between various types of breast cancer. The detection of endogenous sugar receptors by neoglycoproteins is proposed to contribute to an understanding of malignancy-associated alterations in the structure of their potential physiological ligands, the glycoconjugates. Changes in the structure and abundance of such glycoconjugates have commonly been detected with the use of plant lectins in histopathologic studies.

The lithium-chloride-soluble cell-wall layers of Chlamydomonas reinhardii contain several immunologically related glycoproteins

Cell-wall glycoproteins of the unicellular green alga Chlamydomonas reinhardii have been purified from LiCl extracts of intact cells by gel exclusion chromatography and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Antibodies were raised against several polypeptide components isolated from the LiCl extracts. All these antibodies specifically reacted with the cell surface of formaldehyde-fixed cells. They showed cross-reactivity with the different antigens and were also reactive against some other polypeptides present in the LiCl extracts of intact wild-type cells as shown by double-diffusion assays and immunoblot analyses. These antigens were largely missing in LiCl extracts from the cell-wall-deficient mutant CW-15. The pattern of immunologically related cell-wall polypeptides of C. reinhardii varied during the vegetative cell cycle and was found to be also dependent on the growth conditions. Dot-immunobinding assays on chemically modified cell-wall glycoproteins demonstrated differences between the various antibodies with respect to their specificities. Differences were observed especially with respect to their reactivities against chemically deglycosylated cell-wall polypeptides. Chemical deglycosylation generally reduced the binding of the different antibodies indicating that all these antibodies recognize carbohydrate side chains. Only two of these antibody preparations, raised against cell-wall glycoproteins of relative molecular mass 35 and 150 kilodaltons, were found to be strongly reactive against deglycosylated cell-wall polypeptides. When these antibodies were saturated with cell-wall-derived glycopeptides in order to abolish the binding to carbohydrate side chains, they still recognized the same cell-wall polypeptides as did the untreated antibodies. These findings indicate that the cross-reactivity of the different cell-wall polypeptides with the antibodies is not exclusively the consequence of similar glycosylation patterns but is also the result of the presence of similar structures within the non-glycosylated stretches of the polypeptide backbones. Cell walls isolated from growing tobacco pollen tubes contained a single polypeptide component which showed crossreactivity with the antibodies to the cell-wall glycoproteins of C. reinhardii.

Isolation of monoclonal antibodies reacting with peribacteriod membranes and other components of pea root nodules containing Rhizobium leguminosarum

Plant and bacterial antigens contributing to nodule development and symbiosis in pea (Pisum sativum L.) roots were identified after isolation of a set of monoclonal antibody (McAb)-producing hybridoma lines. Rats were immunised with the peribacteriod material released by mild osmotic shock treatment from membrane-enclosed bacteroids of Rhizobium leguminosarum bv. viceae. In order to diversify the range of McAb specificities, this material was either used as immunogen directly (method 1), or after immunodepletion of a set of glycoprotein and lipopolysaccharide antigens (method 2), or after deglycosylation (method 3). After fusion and screening of cloned hybridoma lines, these three immunisation methods gave respectively 4, 2 and 1 classes of McAb with unique antigen specificities. Ultrastructural immunogold localisation studies showed four different antigens to be present on peribacteriod and plasma membranes (identified by MAC 64, 202, 206 or 209); in addition, a glycoprotein of plant origin but present in the infection-thread matrix was identified by MAC 204. Although none of the epitopes recognised by these McAb was nodule-specific, several were found to be more abundant in extracts of nodule tissue than in uninfected roots (MAC 64, 202, 204, 206). Two McAb reacted with new bacterial antigens: MAC 203 identified a bacterial antigen expressed upon infection but not in free-living cultures of Rhizobium, and MAC 115 identified a bacterial polypeptide (55 kdaltons) that was present in both free-living and bacteroid forms. There were also some McAb of broader specificity that react with antigens present in both plant and bacterial cytoplasms.

Monoclonal antibodies to human transferrin: epitopic and phylogenetic analysis

Monoclonal antibodies (MAbs) are useful reagents for the study of the structure and evolution of specific epitopes. Two MAbs of IgG1 isotype, Tf-1 and Tf-2, which bind human transferrin have been produced and characterized. Both specifically recognize transferrin on immunoblots of serum. Proteolytic digestion with papain or chymotrypsin destroys the epitope recognized by Tf-1 but not Tf-2, demonstrating that the MAbs recognize distinct epitopes. Both epitopes are not recognized after treatment with 2-mercaptoethanol, suggesting that disulfide bond dependent tertiary structure is necessary for epitope integrity. Removal of carbohydrate moieties by treatment with trifluoromethane sulfonic acid likewise results in loss of reactivity. Neither MAb reacts with transferrin of mouse, rabbit or bovine origin. Both were tested for reactivity to a total of ten primate transferrins and showed different patterns of reaction. Tf-2 recognized human, chimpanzee and gorilla transferrins, whereas Tf-1 reacted with all Old World monkeys and one of three New World monkeys tested. Thus, Tf-1 and Tf-2 recognize transferrin epitopes with differential phylogenetic conservation and which are dependent not only on primary aminoacid sequence, but also upon tertiary structure and glycosylation.

Immunotoxins containing single-chain ribosome-inactivating proteins

We have summarized what is currently known about the distribution, biological role, and the mechanism of action of the single chain ribosome-inactivating proteins and described the purification of one of them, gelonin, as an example. ITs have been made with several of these proteins and, depending upon the antibody used for conjugation, these immunoconjugates can show specific in vitro cytotoxicity which is similar to that shown by equivalent ITs prepared with ricin A chain. The most potent of these conjugates have shown antitumor efficacy in a variety of animal tumor models, including both syngeneic rodent tumors and xenografts in nude or immunosuppressed mice. An important point needs to be addressed, however, before concluding that ITs containing single chain toxins will be clinically useful. A major problem with this approach is that it is likely that both the antibody and the toxin components of these conjugates will be immunogenic. Both antitoxin and antixenogenic immunoglobulin responses have been shown to occur in animals after infusion of IT, although it has not yet been clearly demonstrated that such antibody responses adversely effect the pharmacokinetics or the efficacy of immunoconjugates. Thus, preliminary enthusiasm over the efficacy of these new reagents must be tempered with the knowledge that their use in the clinic may be limited by the host immune responses or other as yet undefined factors. The fact that there are many immunologically distinct single chain ribosome-inactivating proteins does suggest one way of evading the antitoxin response, by a sequential treatment with a panel of immunoconjugates, each containing a different single chain toxin.

Biochemical characterization of polypeptide components involved in neurite fasciculation and elongation

Polypeptide components and carbohydrate linkage types of F11 antigen and G4 antigen, two chick cell-surface glycoproteins implicated in neurite fasciculation and elongation [Rathjen, F.G., Wolff, J.M., Bonhoeffer, F. and Rutishauser, U. (1987) J. Cell Biol. 104, 343-353], have been studied in comparison to mouse L1 antigen. Tryptic fingerprint analysis does not reveal any relation of the 130-kDa components of G4 or F11 antigens to each other or to neural cell-adhesion molecules. The 180/190-kDa component of G4 antigen comprises parts of the 130-kDa and 80/65-kDa components and shares a sequence corresponding to the amino terminus of the G4 130-kDa component as shown serologically with anti-peptide sera. This closely parallels the relationship found for mouse L1 antigen components. In contrast, the F11 170-kDa component is different from the F11 130-kDa component, as shown serologically and by fingerprint analysis. A combination of chemical and enzymatic deglycosylation methods reveals that while O-glycosylation cannot be detected F11 130-kDa, G4 130-kDa and L1 140-kDa components contain N-linked carbohydrates. Endoglycosidase H treatment shows that the oligosaccharides present in the G4 130-kDa component and mouse L1 are mostly of the complex type, while the F11 130-kDa component consists of two populations, one containing mainly complex-type carbohydrates and a second containing high-mannose/hybrid-type carbohydrates.

The plant vacuolar protein, phytohemagglutinin, is transported to the vacuole of transgenic yeast

Phytohemagglutinin (PHA), the major seed lectin of the common bean, Phaseolus vulgaris, accumulates in the parenchyma cells of the cotyledons. It has been previously shown that PHA is cotranslationally inserted into the endoplasmic reticulum with cleavage of the NH2-terminal signal peptide. Two N-linked oligosaccharide side chains are added, one of which is modified to a complex type in the Golgi apparatus. PHA is then deposited in membrane-bound protein storage vacuoles which are biochemically and functionally equivalent to the vacuoles of yeast cells and the lysosomes of animal cells. We wished to determine whether yeast cells would recognize the vacuolar sorting determinant of PHA and target the protein to the yeast vacuole. We have expressed the gene for leukoagglutinating PHA (PHA-L) in yeast under control of the yeast acid phosphatase (PHO5) promoter. Under control of this promoter, PHA-L accumulates to 0.1% of the total yeast protein. PHA-L produced in yeast is glycosylated as expected for a yeast vacuolar glycoprotein. Cell fractionation studies show that PHA-L is efficiently transported to the yeast vacuole. This is the first demonstration that vacuolar targeting information is recognized between two highly divergent species. A small proportion of yeast PHA-L is secreted which may be due to inefficient recognition of the vacuolar sorting signal because of the presence of an uncleaved signal peptide on a subset of the PHA-L polypeptides. This system can now be used to identify the vacuolar sorting determinant of a plant vacuolar protein.

Schistosoma mansoni: stimulation of artificial granuloma formation in vivo by carbohydrate determinants

A subset of Schistosoma mansoni egg glycoproteins that share a common carbohydrate epitope recognized by monoclonal antibody 128C3 was shown to induced formation of hepatic granulomata when conjugated to Sepharose beads and injected into the portal circulation of naive mice. Concanavalin-binding egg glycoproteins exhibited more granuloma-inducing activity than did total egg extract, although deglycosylated egg proteins also induced granulomata; thus, both amino acid and carbohydrate epitopes appeared to be involved. Glycoproteins derived from adult male worms also were active, indicating that immunological processes responsible for granuloma formation may not be absolutely stage specific.

Comparative classification of Leptospira serovars of the Pomona group by monoclonal antibodies and restriction-endonuclease analysis

The serovars of the Pomona group of Leptospira interrogans are antigenically closely related and can be classified only with difficulty by conventional typing methods. Monoclonal antibodies (MCAs) were prepared to serovars of the Pomona group. The MCAs were directed against antigens of polysaccharide nature. A battery of six MCAs was selected for the classification of Pomona group reference strains. These MCAs could be used for the typing of all Pomona group strains and unknown isolates. Alternatively, DNA was extracted from the same strains and isolates and digested with restriction enzymes. The patterns that were obtained after gel separation of the DNA digests were characteristic and also allowed classification. Restriction enzyme analysis was complicated but gave detailed information. Classification with MCAs could be easily and rapidly performed.

Elicitor induction of the synthesis of a novel lectin-like arabinosylated hydroxyproline-rich glycoprotein in suspension cultures of Phaseolus vulgaris L

A novel lectin-like glycoprotein which accumulates in response to fungal elicitor action has been characterised in endomembranes from suspension cultures of French bean (Phaseolus vulgaris L.). The lectin, which has specificity towards N-acetylglucosamine oligomers, consists of a polypeptide of apparent molecular weight (Mr) 31 000 which is rich in glycine and contains 6.7% hydroxyproline O-linked to arabinose-containing oligosaccharides to give a glycoprotein of Mr 42500. A dual-labelling technique has been used to identify changes in the synthesis of the glycoprotein in cells exposed to fungal elicitor molecules. Thus, incorporation of [(14)C]proline into membranes in vivo and of [1(-3)H]arabinose from uridine 5'-diphosphate [1(-3)H]arabinose in vitro and analysis by isoelectric focussing-polyacrylamide gel electrophoresis gave absolute correspondence of the labelled isoform of the glycoprotein. Having established the absence of contaminating polypeptides, subsequent analysis of microsomal fractions bysodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the peak of sythesis of the Mr-42500 glycoprotein occurred 4 h after the addition of fungal elicitor. The changes in the level of incorporation into the glycoprotein monomers were concomitant with increases in the activity of prolyl hydroxylase (EC 1.14.11.2)Incorporation of [(14)C]proline and its subsequent post-translational modification to hydroxyproline in microsomal polypeptides was followed by rapid transfer into the wall with an average t 1/2 of about 7 min. The Mr-42500 glycoprotein was rapidly transferred out of the endomembrane fraction with a t 1/2 of 2 min and could be detected in wall fractions where it became progressively less extractable. The glycoprotein, which clearly differs from bean extensin, accounts for up to 40% of the hydroxyproline newly exported in response to elicitor action. The lectin, which resembles those found in the Solanaceae and which is coinduced with enzymes of phytoalexin synthesis, may play some role in disease resistance.

The establishment of hepatocyte cell surface polarity during fetal liver development

Antibodies to six glycoproteins present in different domains of the hepatocyte plasma membrane were used to study the establishment of cell surface polarity during rat fetal liver development. The proteins were immunoprecipitated from fetal liver homogenates between 14 and 21 days of gestation and quantified by immunoblotting. Aminopeptidase N, CE 9, and HA 321, which reside in the apical, basolateral, and lateral plasma membrane in the adult hepatocyte, respectively, were present in high concentrations at 14 days of gestation and remained high until birth. In contrast, two apical proteins (HA 4 and dipeptidyl peptidase IV) and two basolateral proteins (ASGP receptor and EGF receptor) were first detected between 16 and 18 days of gestation and increased linearly until birth. HA 4 was the only molecule for which the fetal and adult forms differed, with the former having a faster mobility on SDS-PAGE, due to differences in N-linked oligosaccharides. With two exceptions, the localization of the molecules from earliest detection was restricted to the same domain as that in the adult. At 15 days of gestation, HA 321 and a small portion of aminopeptidase were detected on the basolateral membrane. By 21 days both molecules had assumed their adult localization pattern. Our results indicate that the biogenesis of cell surface polarity is an early event, implying that the mechanisms for sorting plasma membrane molecules are functional very early in development. Furthermore, the different patterns of appearance of the six molecules, irrespective of domain, indicate that the biochemical composition of the cell surface changes dramatically during fetal liver development.

Purified cytochrome b from human granulocyte plasma membrane is comprised of two polypeptides with relative molecular weights of 91,000 and 22,000

A new method has been developed for purification of cytochrome b from stimulated human granulocytes offering the advantage of high yields from practical quantities of whole blood. Polymorphonuclear leukocytes were treated with diisopropylfluorophosphate, degranulated and disrupted by nitrogen cavitation. Membranes enriched in cytochrome b were prepared by differential centrifugation. Complete solubilization of the cytochrome from the membranes was achieved in octylglucoside after a 1-M salt wash. Wheat germ agglutinin-conjugated Sepharose 4B specifically bound the solubilized cytochrome b and afforded a threefold purification. Eluate from the immobilized wheat germ agglutinin was further enriched by chromatography on immobilized heparin. The final 260-fold purification of the b-type cytochrome with a 20-30% yield was achieved by velocity sedimentation in sucrose density gradients. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the purified preparation revealed two polypeptides of Mr 91,000 and Mr 22,000. Treatment of the 125I-labeled, purified preparation with peptide:N-glycosidase F, which removes N-linked sugars, decreased relative molecular weight of the larger species to approximately 50,000, whereas beta-elimination, which removes O-linked sugars, had little or no effect on the mobility of the Mr-91,000 polypeptide. Neither of the deglycosylation conditions had any effect on electrophoretic mobility of the Mr-22,000 polypeptide. Disuccinimidyl suberate cross-linked the two polypeptides to a new Mr of 120,000-135,000 by SDS-PAGE. Antibody raised to the purified preparation immunoprecipitated spectral activity and, on Western blots, bound to the Mr-22,000 polypeptide but not the Mr-91,000 polypeptide. Western blot analysis of granulocytes from patients with X-linked chronic granulomatous disease revealed a complete absence of the Mr-22,000 polypeptide. These results (a) suggest that the two polypeptides are in close association and are part of the cytochrome b, (b) provide explanation for the molecular weight discrepancies previously reported for the protein, and (c) further support the involvement of the cytochrome in superoxide production in human neutrophils.

Deglycosylation studies on tracheal mucin glycoproteins

Following several model experiments, conditions were developed for optimal deglycosylation of tracheal mucin glycoproteins. Exposure of rigorously dried material to trifluoromethanesulfonic acid at 0 degree C for up to 8 h results in cleavage of essentially all fucose, galactose, and N-acetylglucosamine, about 80% of the N-acetylneuraminic acid (NeuNAc), and a variable amount of N-acetylgalactosamine (GalNAc), the sugar involved in linkage to protein. Residual N-acetylneuraminic acid is sialidase susceptible and apparently in disaccharide units, presumably NeuNAc2----GalNAc. The remaining N-acetylgalactosamine is mostly present as monosaccharides, and a few Gal beta 1----3GalNAc alpha units are also present; both are cleaved by appropriate enzymatic treatment. The saccharide-free proteins obtained from either human or canine mucin glycoproteins have molecular weights of about 100,000 and require chaotropic agents or detergents for effective solubilization.

Isolation of cDNA clones coding for human tissue factor: primary structure of the protein and cDNA

Tissue factor is a membrane-bound procoagulant protein that activates the extrinsic pathway of blood coagulation in the presence of factor VII and calcium. lambda Phage containing the tissue factor gene were isolated from a human placental cDNA library. The amino acid sequence deduced from the nucleotide sequence of the cDNAs indicates that tissue factor is synthesized as a higher molecular weight precursor with a leader sequence of 32 amino acids, while the mature protein is a single polypeptide chain composed of 263 residues. The derived primary structure of tissue factor has been confirmed by comparison to protein and peptide sequence data. The sequence of the mature protein suggests that there are three distinct domains: extracellular, residues 1-219; hydrophobic, residues 220-242; and cytoplasmic, residues 243-263. Three potential N-linked carbohydrate attachment sites occur in the extracellular domain. The amino acid sequence of tissue factor shows no significant homology with the vitamin K-dependent serine proteases, coagulation cofactors, or any other protein in the National Biomedical Research Foundation sequence data bank (Washington, DC).

MB1, a quail leukocyte/vascular endothelium antigen: characterization of the lymphocyte-surface form and identification of its secreted counterpart as alpha 2-macroglobulin

A monoclonal antibody (alpha-MB1) binds to a cell surface marker expressed throughout ontogeny and adult life by vascular endothelial and hemopoietic cells of the quail, with the exception of erythrocytes, although it was raised against the heavy chain of quail immunoglobulin M. In addition to an 80 kDa polypeptide accounting for immunoglobulin mu chain, alpha-MB1 stains intensely a 180-kDa band on Western blots of reduced plasma proteins. We have previously characterized MB1 antigens of quail endothelial cells as glycoproteins of apparent molecular masses ranging from 80 to 200 kDa and provided evidence for the participation of vascular endothelium in the secretion of alpha-MB1-positive plasma components. We demonstrate here that this circulating material is the proteinase inhibitor alpha 2-macroglobulin. Furthermore, the MB1 antigens immunoprecipitated from lymphocytes are shown to be essentially similar to their endothelial counterparts, suggesting that the same molecular complex is expressed by all the elements of the hemangioblastic cell lineage. Finally, the cross reactivity of the alpha-MB1 antibody with immunoglobulin mu chain is confirmed and shown to occur via a carbohydrate epitope.

Identification of an endosomal antigen specific to absorptive cells of suckling rat ileum

A membrane fraction enriched in apical endosomal tubules was isolated from absorptive cells of suckling rat ileum and used as an immunogen to generate anti-endosome monoclonal antibodies. By immunofluorescence, one of these antibodies bound exclusively to the region of the apical endocytic complex in ileal absorptive cells, but not to other cell types. Immunoblot analysis showed the antigen as a diffuse 55-61-kD band which was highly enriched in the endosome fraction over whole-cell homogenate. The antigen appears to be an intramembrane glycoprotein: it partitioned primarily in the detergent phase after TX-114 extraction, and shifted to 44 kD after chemical deglycosylation. EM immunocytochemistry showed that the antibody bound to the luminal side of endosomal tubule membranes, a portion of endosomal vesicle membranes, and in endocytic pits of apical plasma membranes. However, it did not bind to multivesicular bodies, the giant lysosome, or other organelles. Immunocytochemistry after uptake with adsorbed or soluble tracer proteins showed that the antigen labeled portions of both prelysosomal pathways previously described in these cells (Gonnella, P.A., and M. R. Neutra, 1984, J. Cell Biol., 99:909-917). The function of this glycoprotein is not known, but inasmuch as it has been detected only in absorptive cells of suckling rat ileum, it may serve a function specific to these cells. Nevertheless, this endosomal antigen, designated glycoprotein (gp) 55-61, will serve as a useful marker for exploring membrane dynamics in early stages of the endocytic pathway.

The insulin-secretory-granule carboxypeptidase H. Purification and demonstration of involvement in proinsulin processing

A carboxypeptidase B-like enzyme was detected in the soluble fraction of purified insulin secretory granules, and implicated in insulin biosynthesis. To investigate the role of this activity further, we purified the enzyme from rat insulinoma tissue by gel-filtration chromatography and affinity elution from p-aminobenzoyl-arginine. A yield of 42%, with a purification factor of 674 over the homogenate, was achieved. Analysis of the purified carboxypeptidase by SDS/polyacrylamide-gel electrophoresis under either reducing or non-reducing conditions showed it to be a monomeric protein of apparent Mr 55,000. The preparation was also homogeneous by high-performance gel-filtration chromatography. The enzyme bound to concanavalin A, showing it to be a glycoprotein. Amino acid analysis or chemical deglycosylation and SDS/polyacrylamide-gel electrophoresis indicated a protein Mr of 50,000, suggesting a carbohydrate content of approx. 9% by weight. The purified enzyme was able to remove basic amino acids from the C-terminus of proinsulin tryptic peptides to generate insulin, but did not further degrade the mature hormone. It was inhibited by EDTA, 1,10-phenanthroline and guanidinoethylmercaptosuccinic acid, and stimulated 5-fold by CoCl2. The pH optimum of the conversion of diarginyl-insulin into insulin was in the range 5-6, with little activity above pH 6.5. Activity was also expressed towards a dansylated tripeptide substrate (dansyl-phenylalanyl-leucyl-arginine; Km = 17.5 microM), and had a pH optimum of 5.5. These properties are indistinguishable from those of the activity located in secretory granules, and are compatible with the intragranular environment. The insulin-secretory-granule carboxypeptidase shared several properties of carboxypeptidase H from bovine adrenal medulla and pituitary. We propose that the carboxypeptidase that we purified is the pancreatic isoenzyme of carboxypeptidase H (crino carboxypeptidase B; EC 3.4.17.10), and is involved in the biosynthesis of insulin in the pancreatic beta-cell.

Comparative binding of murine and human monoclonal antibodies reacting with myelin-associated glycoprotein to myelin and human lymphocytes

Human monoclonal IgM antibodies present in the blood of some patients with peripheral neuropathy and murine hybrid IgM antibodies C5 and C6, raised against myelin-associated glycoprotein, and HNK-1, raised against the human T cell line HSB-2, all bind to the carbohydrate moiety of myelin-associated glycoprotein. The relative avidity of the monoclonal antibodies was HNK-1 greater than C5/C6 much greater than human IgM, as determined in a competitive binding radioimmunoassay. HNK-1 bound myelin equally well at incubation temperatures between 4 degrees C and 37 degrees C; the human antibodies bound significantly only at 4 degrees C; and C6 bound best at 4 degrees C, less strongly at 20 degrees C and did not bind at 37 degrees C. All of the antibodies bound to a band corresponding to myelin-associated glycoprotein on immunoblots of human CNS myelin proteins in addition to several other antigens. Flow cytometric studies revealed that the murine but not the human antibodies bind to peripheral blood lymphocytes. Taken together, these data suggest that the antibodies probably recognize the same epitope but bind with different avidity.

Assembly of cell-wall glycoproteins of Chlamydomonas reinhardii: Oligosaccharides are added in medial and trans Golgi compartments

A series of monoclonal antibodies and a polyclonal antiserum have been used to investigate the localisation and pathway of biosynthesis of the cell-wall hydroxyproline-rich glycoprotein 2BII in the alga Chlamydomonas reinhardii. Glyco-protein precursors were detected within the endoplasmic reticulum using a polyclonal antiserum raised to the deglycosylated 2BII. Monoclonal antibodies which are known to recognise different carbohydrate epitopes of 2BII were found to label two distinct regions of the Golgi stack. The immunolabelling results demonstrate that there is compartmentation of protein synthesis and glycosylation steps for these O-glycosidically linked glycoproteins. Newly synthesised glycoproteins are transported from the Golgi apparatus to the cell surface via two distinct routes. They then undergo assembly into a cell wall, the inner wall layer being formed first and probably functionaing as a template within which the outer crystalline wall layers are assembled.

A family of serine esterases in lytic granules of cytolytic T lymphocytes

Cytoplasmic granules of cytolytic T lymphocytes (CTLs) contain, in addition to the pore-forming protein perforin, a family of highly homologous serine esterases, granzymes A-H. The serine esterase affinity label diisopropyl fluorophosphate reacts strongly with granzymes A and D, to a lesser extent with B, E, F, G, and H, and not at all with C and F. For granzymes A and D, synthetic substrates have been found. Antibodies raised against granzyme B strongly cross-react with A, G, and H, and antibodies to granzyme D recognize C, E, and F. These antigenic relationships correlate with similarities in the N-terminal amino acid sequences. At least 60% homology is observed between the eight proteins, and all are similar to rat mast cell protease 2. Sequence analysis suggests the identity of granzyme A with a protease predicted from a CTL-specific cDNA clone (H factor) and of granzyme B, G, or H with a protein encoded by the CTL-specific cDNA clone CTLA 1/CCP 1.

The chicken erythrocyte-specific MHC antigen. Characterization and purification of the B-G antigen by monoclonal antibodies

Mouse monoclonal antibodies with B-G antigen (major histocompatibility complex class IV) specificity were obtained after immunization with erythrocytes or partially purified B-G antigen. The specificities of the hybridoma antibodies were determined by precipitation of B-G antigens from 125I-labeled chicken erythrocyte membranes (CEM) followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. The B-G antigen had an approximate molecular mass of 46-48 kd in reduced samples, depending on the haplotype, and in unreduced samples contained either dimers (85 kd), when labeled erythrocytes were the antigen source, or trimers (130 kd), when B-G was purified and precipitated from CEM. The B-G antigen was unglycosylated as studied by in vitro synthesis in the presence or absence of tunicamycin, binding experiments with lectin from Phaseolus limensis, and treatment of purified B-G antigen with Endoglycosidase-F or trifluoromethanesulfonic acid. Two-way sequential immunoprecipitation studies of erythrocyte membrane extracts with anti-B-G alloantisera and monoclonal antibodies revealed only one population of B-G molecules. Pulse-chase experiments have shown B-G to be synthesized as a monomer, with dimerization taking place after 20-30 min. No change in the monomer's molecular mass due to posttranslational modifications was revealed. The antigen was purified from detergent extract of CEM by affinity chromatography with a monoclonal antibody, and then reduced and alkylated and affinity-purified once more. Finally, reverse-phase chromatography resulted in a pure product. The B-G antigen was identified in the various fractions by rocket immunoelectrophoresis. The final product was more than 99% pure, as estimated by SDS-PAGE analysis followed by silver stain of proteins. The yield from the affinity chromatography step was 3-4 micrograms B-G/ml blood, calculated from Coomassie-stained SDS-PAGE of B-G using ovalbumin standards. The monoclonal antibodies were also used to identify the B-G (class IV) precipitation arc in crossed immunoelectrophoresis. No common precipitate with the B-F (class I) antigen was observed.

Biosynthesis, glycosylation, and partial N-terminal amino acid sequence of the T-cell-activating protein TAP

We have characterized the TAP molecule, an Ly-6 linked T-cell-activating glycoprotein. The three TAP bands that are precipitated from metabolically labeled cells display a common migration pattern in isoelectric focusing/NaDodSO4/PAGE gels and have common N-terminal sequences. This sequence is rich in cysteine and is homologous to that previously reported for the Ly-6.1E antigen. We, therefore, compared TAP and Ly-6.1E biochemically and found them to be structurally distinct. Given the role of TAP in T-cell activation, we further studied whether the molecule was phosphorylated. We have not found evidence for phosphorylation of the TAP protein. The carbohydrates present on the TAP molecule are resistant to peptide N-glycosidase F in vitro and tunicamycin in vivo. The upper band of the TAP triplet is susceptible to treatment with trifluoromethanesulfonic acid and thus seems to be of the O-linked rather than of the N-linked variety. The biosynthetic processing of TAP was studied in pulse-chase experiments. The middle band of the TAP triplet appears to be the earliest detectable species. Its conversion to the O-linked high molecular weight species can be blocked by monensin.

Analysis of the biological properties of antibodies raised against intact and deglycosylated porcine zonae pellucidae

Zonae pellucidae (ZP) were isolated from 1,500 porcine ovaries and heat solubilized to generate approximately 15 mg ZP glycoprotein. Analysis of this material by isoelectric focusing, one-dimensional electrophoresis, and gas chromatography indicated the presence of a major glycoprotein species that exhibited considerable microheterogeneity with respect to its charge (pI 7.5-3.5) and molecular mass (45-85 kDa) and that contained 39.6% carbohydrate, predominantly N-acetylglucosamine. Chemical deglycosylation of porcine ZP using trifluoromethanesulphonic acid (TFMS) resulted in the production of five discrete protein bands on one-dimensional sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS/PAGE) with molecular masses of 66, 52, 36, 32, and 16 kDa. Antisera raised in rabbits and marmosets to ZP and/or deglycosylated ZP (DGZP) were used in immunoblotting experiments to demonstrate the retention of immunogenicity by DGZP and the cross-reactivity of the antisera with their heterologous antigen. These studies indicated that antisera that were capable of inhibiting the fertility of primates in vivo and the penetration of the human ZP in vitro reacted preferentially with 3 of the 5 products of deglycosylation, with molecular masses of 66, 52, and 36 kDa. Anti-DGZP antibodies were also shown to interact with intact porcine and human ZP and, with the latter, to block the ability of human spermatozoa to both bind to and penetrate this structure.

The zygote cell wall of Chlamydomonas reinhardii: a structural, chemical and immunological approach

The zygote cell wall of Chlamydomonas reinhardii has been studied using structural, chemical and immunological methods. Monoclonal antibodies and polyclonal antisera that were originally raised to the major hydroxyproline-rich glycoproteins of the vegetative cell wall were used to probe the zygote wall for common antigenic components. These antibodies cross-reacted strongly and specifically with components of the zygote cell wall, and were used to show the origin, route of transport, and the location of these antigens within the zygote cell wall. The zygote cell wall contained about 10% protein, with hydroxyproline accounting for 22.5 mol % of the total amino acids present. Glucose was the most abundant sugar residue, and accounted for 56% of the total sugar present. Gas liquid chromatography-mass spectrometry showed the presence of a (1-3)β-D-glucan as the major structural polysaccharide within the zygote cell wall. The (1-3)β-D-glucan was detected and localised within the zygote cell wall by immunogold labelling of thin sections. Using an antiserum directed against (1-3)β-D-linked glucose units, this polysaccharide was found to be consistently present within the non-staining layer of both young and mature zygote cell walls. (1-3)β-D-Glucan was also detected in other wall layer using higher concentrations of antiserum. No intracellular labelling was found, indicating that the plasmamembrane is the site for the synthesis of this polysaccharide within the Chlamydomonas zygote.

Characterization and cloning of fasciclin III: a glycoprotein expressed on a subset of neurons and axon pathways in Drosophila

To identify candidates for neuronal recognition molecules in Drosophila, we used monoclonal antibodies to search for surface glycoproteins expressed on subsets of axon bundles (or fascicles) during development. Here we report on the characterization and cloning of fasciclin III, which is expressed on a subset of neurons and axon pathways in the Drosophila embryo. Fasciclin III is also expressed at other times and places including transient segmentally repeated patches in the neuroepithelium and segmentally repeated stripes in the body epidermis. Antisera generated against each of four highly related forms of the protein were used for cDNA expression cloning to identify a single gene, which was confirmed to encode fasciclin III by tissue in situ hybridization and genetic deficiency analysis.

Purification and partial characterization of a tumour-metastasis-associated high-Mr glycoprotein from rat 13762NF mammary adenocarcinoma cells

The expression of a high-Mr sialogalactoprotein (gp580) on rat 13762NF mammary adenocarcinoma cells was identified and correlated with spontaneous metastatic potential to colonize lung [Steck & Nicolson (1983) Exp. Cell Res. 147, 255-267]. Using a highly metastatic tumour-cell clone, MTLn3, we isolated and characterized gp580 from cells growing in vitro and in vivo in the mammary fat-pads of Fischer 344 rats. The glycoprotein was extracted with 4 M-guanidinium chloride/4% Zwittergent 3-12 solution in the presence of proteinase inhibitors. The extracts were then subjected to dissociative CsCl-density-gradient centrifugation, gel filtration on Sepharose CL-2B columns and ion-exchange chromatography on DEAE-Sephacel. The isolated glycoprotein possessed low electrophoretic mobility in SDS/polyacrylamide gels, and after desialylation bound 125I-labelled peanut agglutinin. Electrophoresis of gp580 in polyacrylamide-gradient gels resulted in a diffuse but homogeneous migrating band of Mr approx. 55,000. After removal of carbohydrate, gp580 was demonstrated to have a protein core of Mr approx. 150,000. The gp580 had a high density (1.430 g/ml) on isopycnic centrifugation in 4 M-guanidinium chloride and was resistant to most proteinases and other degradative enzymes, suggesting a mucin-like structure. Amino acid and carbohydrate analyses revealed that gp580 has high contents of serine, threonine, glutamic acid, aspartic acid, glucosamine and galactosamine; several acidic and neutral oligosaccharides were obtained from alkaline-borohydride digests. Cellular localization studies suggested that gp580 is associated mainly with the cell-surface and extracellular-matrix fractions of MTLn3 cells.

The development of monospecific antibodies against human thromboplastin apoprotein (apoprotein III) and their application in the immunocytochemical detection of the antigen in blood cells

Human thromboplastin apoprotein (apoprotein III) purified by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) was purified a further 2-4 fold by PAGE in the presence of digitonin. Subsequent line immunoelectrophoresis of the protein revealed several lines, only one of which contained inhibitory antibodies. New inhibitory antibodies which were raised by using this particular line to immunize rabbits produced only a single line in immunoelectrophoresis of apoprotein III, with precipitated inhibitory antibodies being present only in the line. When these antibodies were used in electroblot immunobinding studies of crude thromboplastin after SDS-PAGE staining was found mainly in a single band of MW about 50,000, but also to some extent in immunologically related higher MW material. Prior deglycosylation of the thromboplastin using trinitrobenzenesulfonic acid resulted in a shift of the bulk of the main band representing an apparent MW reduction of 16%, and a corresponding shift in the position of protein with the capacity to bind inhibitory antibodies. Besides being a good criterion of specificity of the antibodies this also suggests that non-carbohydrate parts of apoprotein III may be involved in the interaction with Factor VII. Immunoperoxidase staining of unstimulated or endotoxin stimulated blood cells using the antibodies revealed the presence of significant amounts of apoprotein III only in stimulated monocytes, apparently available on the surface of the cells since it was detectable also by preembedding staining of fixed cells in suspension. The result is strong evidence that apoprotein III is synthesized de novo in monocytes upon endotoxin stimulation.

Schistosoma mansoni shares a protective carbohydrate epitope with keyhole limpet hemocyanin

The glycanic epitope of the 38,000 Mr Schistosoma mansoni schistosomula major immunogen defined by the IPLSm1 protective mAb was identified in the hemocyanin of the marine mollusc Megathura crenulata, better known as KLH. This antigenic community was exploited to investigate further the biological properties of this epitope. KLH was shown to strongly inhibit the binding of IPLSm1 mAb to its 38,000 Mr target antigen. Immunization of naive LOU rats with KLH elicited the production of anti-S. mansoni antibodies capable of immunoprecipitating the 38,000 Mr schistosomulum antigen. Antibodies to KLH mediated a marked eosinophil-dependent cytotoxicity and passively transferred immunity towards S. mansoni infection. Finally, rats immunized with KLH were significantly protected against a challenge with S. mansoni cercariae. The deglycosylation of KLH completely abolishes its immunological and functional KLH properties, indicating the participation of an oligosaccharidic epitope of the native KLH that is also recognized by the sera of S. mansoni-infected patients. These observations provide new opportunities of access to the well-defined structure of a glycanic epitope potentially available for the immunoprophylaxis and seroepidemiology of schistosomiasis, and a new approach to the isotypic response towards a well-chemically defined epitope.

Extracellular phytase (E.C. 3.1.3.8) from Aspergillus ficuum NRRL 3135: purification and characterization

Extracellular phytase from Aspergillus ficuum, a glycoprotein, was purified to homogeneity in 3 column chromatographic steps using ion exchange and chromatofocusing. Results of gel filtration chromatography and SDS-polyacrylamide gel electrophoresis indicated the approximate molecular weight of the native protein to be 85-100-KDa. On the basis of a molecular weight of 85-KDa, the molar extinction coefficient of the enzyme at 280 nm was estimated to be 1.2 X 10(4) M-1 cm-1. The isoelectric point of the enzyme, as deduced by chromatofocusing, was about 4.5. The purified enzyme is remarkably stable at 0 degree C. Thermal inactivation studies have shown that the enzyme retained 40% of its activity after being subjected to 68 degrees C for 10 minutes, and the enzyme exhibited a broad temperature optimum with maximum catalytic activity at 58 degrees C. The Km of the enzyme for phytate and p-nitrophenylphosphate is about 40 uM and 265 uM, respectively, with an estimated turnover number of the enzyme for phytate of 220 per sec. Enzymatic deglycosylation of phytase by Endoglycosidase H lowered the molecular weight of native enzyme from 85-100-KDa to about 76-KDa; the digested phytase still retained some carbohydrate as judged by positive periodic acid-Schiff reagent staining of the electrophoresed protein. Immunoblotting of the phytase with monoclonal antibody 7H10 raised against purified native enzyme recognized not only native but also partially deglycosylated protein.

The vasoactive intestinal peptide receptor on intact human colonic adenocarcinoma cells (HT29-D4). Evidence for its glycoprotein nature

We have previously shown that the mono [125I]iodinated vasoactive intestinal peptide (125I-VIP) could be covalently cross-linked on intact colonic adenocarcinoma cells (HT29). A major Mr 67,000 and a minor Mr 120,000 cross-linked polypeptides have been characterized [Muller, Luis, Fantini, Abadie, Giannellini, Marvaldi & Pichon (1985) Eur. J. Biochem. 151, 411-417]. The glycoprotein nature of these species was investigated using endo-beta-acetylglucosaminidase F (Endo F) treatment, enzymic and chemical desialylation and wheat germ agglutinin (WGA)-Sepharose affinity chromatography. Affinity-labelled VIP-binding proteins solubilized by Nonidet P-40 bound to WGA-Sepharose and could be eluted specifically with N-acetyl-D-glucosamine. Treatment with Endo F resulted in an increased electrophoretic mobility of both polypeptides. The major and the minor VIP-binding proteins were converted respectively into Mr 47,000 and 100,000 species, indicating removal of 20 kDa of N-linked oligosaccharides. Deglycosylation with trifluoromethanesulphonic acid also led to a 20 kDa loss in mass of the Mr 67,000 component, indicating the absence of additional O-linked sugars on this polypeptide. The presence of sialic acid on the major VIP-binding protein was demonstrated after treatment of intact cells with neuraminidase or by chemical desialylation with hydrochloric acid. We conclude from this study that the VIP receptor from intact HT29-D4 cells is a glycoprotein with N-linked oligosaccharide side chains containing sialic acid.

Sequence analysis of carcinoembryonic antigen: identification of glycosylation sites and homology with the immunoglobulin supergene family

A direct method for the determination of N-linked glycosylation sites in highly glycosylated proteins is described. Carcinoembryonic antigen (CEA) and a nonspecific crossreacting antigen (NCA) were chemically deglycosylated, and peptide maps were prepared by reverse-phase HPLC. The peptides were sequenced on a gas-phase microsequencer, and glycosylation sites were identified as the phenylthiohydantoin derivative of N-acetylglucosaminylasparagine. The sequences were confirmed by fast atom bombardment mass spectrometry. Highly homologous, extended amino-terminal sequences were determined for CEA and two NCAs, NCA-95 and NCA-55. Cysteine-containing sequences for CEA and NCA-95 show up to 95% sequence homology, and the CEA sequences also show internal sequence homologies. A comparison of the CEA sequences with known protein sequences suggests that CEA may be a member of the immunoglobulin supergene family. The protein sequence data have been used to identify a genomic DNA clone for one of the NCA antigens [Thompson, J., Pande, H., Paxton, R. J., Shively, L., Padma, A., Simmer, R. L., Todd, C. W., Riggs, A. D. & Shively, J. E. (1987) Proc. Natl. Acad. Sci. USA, in press] and a cDNA clone for CEA [Zimmermann, W., Ortlieb, B., Friedrich, R. & von Kleist, S. (1987) Proc. Natl. Acad. Sci. USA, in press].

Phylogenetically conserved antigen on nerve cells and lymphocytes resembles myelin-associated glycoprotein

The HNK-1 (Leu 7) and NC-1 monoclonal antibodies, raised against a human T-cell line and against nerve cells of quail embryos, respectively, have been shown to bind to a shared epitope present on the surface of human large granular lymphocytes and on nerve cells in species ranging from amphibians to humans. We demonstrate that a related antigen is also expressed on the lymphocyte surface in the avian central lymphoid organs, thymus and bursa, and in the spleen during embryonic and adult life. The expression of the HNK-1/NC-1-reactive determinant differs remarkably in the bursal and thymic compartments, antigen expression being stabilized at a high level early in development of the bursa, whereas its expression fluctuates in the thymus. The material immunoprecipitated from bursal and thymic lymphocytes by the HNK-1/NC-1 antibodies exhibits the same relative molecular mass as myelin-associated glycoprotein, which is one of the molecules recognized by these antibodies in the nervous system. Together with the observation that an antiserum reactive with the protein part of chicken myelin-associated glycoprotein detects similar material in membrane extracts of HNK-1/NC-1-positive thymocytes, this suggests that a molecule sharing structural analogies with this nerve cell component is expressed on cells of the immune system.