Deglycosylation of glycoproteins by trifluoromethanesulfonic acid

Immunochemistry of the HLA class II molecules isolated from a mouse cell transfected with DQ alpha and beta genes from a DR4 haplotype

Cells from a mouse B lymphoma were transfected by DQ alpha and DQ beta genes derived from a DR4 haplotype. Quantitatively, the resulting expression of human class II molecules was similar to that of human B lymphoblastoid cell lines. Qualitatively, the transformant class II molecules differed from "normal" class II molecules in their carbohydrate moiety. As for their antigenic specificity, they were shown to carry two determinants previously identified on DQ molecules controlled by DR4 haplotypes, i.e., DQw3 and DCHON. The transformant molecules did not carry a third DR4-associated specificity, DC5 (equivalent to TA10), and must possess a structure allelic to DC5. However, no corresponding alloantigenic specificity was detected by a screening of relevant alloantisera.

Renal gamma-glutamyl transpeptidases: influence of glycosylation on the electrophoretic behavior and molecular weights of their subunits

The molecular weights (Mr) of mammalian renal gamma-glutamyl transpeptidase light subunits vary from 21 to 25 K; a much broader range is seen for the large subunit (51 to 72 K). However, chemical deglycosylation of these enzymes (rat, human, and bovine) yields subunits each of which exhibits identical Mr (41 and 19 K for the heavy and light subunits, respectively), suggesting strong similarity between the peptide backbones of these glycoproteins. Immunological data also indicate homologies between these enzymes. The difference observed in the Mr of native subunits thus seem to be related to the extent and nature of glycosylation of these proteins.

Carbohydrate-binding proteins of tumor lines with different growth properties. II. Changes in their pattern in clones of transformed rat fibroblasts of differing metastatic potential

A tumor model system of clones of myeloproliferative sarcoma virus (MPV)-transformed rat fibroblasts (NRK) with different growth properties and metastatic potential was studied. The relationship between metastatic behavior and composition of carbohydrate-binding proteins (lectins) was analyzed by affinity chromatography. The metastatic variant differs qualitatively from its parental clone in the presence of galactoside-binding proteins at apparent molecular weight of 42 kDa. The alpha-glucosyl-binding proteins at apparent molecular weights of 67 kDa and 53 kDa and a galactoside-binding protein of apparent molecular weight of 34 kDa, however, are not detectable in the metastatic variant in comparison to its parental clone. In this respect the parental clone shows closer resemblance to the clone 5-8#1 with different growth properties and low metastatic potential than to its own metastatic variant. Furthermore, only the parental clone has a melibiose- and a mannan-binding protein of an apparent molecular weight of 64 kDa and 14 kDa, respectively. Rosette formation as model system for intercellular interaction reveals differences in the inhibition pattern with sugar between the two clones 5-8#1 and 5-20#20, whereas the metastatic variant 5-20#20 (s) exhibits drastically reduced capability to form rosettes. Initial experiments demonstrate the feasibility of drug targeting to transformed fibroblasts via carbohydrate-binding proteins.

Characterization of a thrombomodulin cDNA reveals structural similarity to the low density lipoprotein receptor

We have isolated a partial-length cDNA for bovine thrombomodulin from a lambda gt11 bovine adrenal capillary endothelial cell expression library. This was accomplished by immunoscreening with rabbit anti-thrombomodulin IgG heteroantibody and then rescreening with the initial positive recombinant insert. The cDNA obtained was authenticated by showing that it coded for the primary structure of two separate regions of bovine thrombomodulin. The nucleotide sequence of the largest cDNA allowed us to establish the structure of about 80% of the mature thrombomodulin transcript, which encodes the C-terminal half of the polypeptide. This membrane component is structurally similar to coated-pit receptors and is organized into domains that resemble those of the low density lipoprotein receptor.

Production and characterization of monoclonal antibodies against myelin-associated glycoprotein

Monoclonal antibodies against myelin-associated glycoprotein were generated by fusing mouse myeloma cells with spleen lymphocytes from BALB/c mice immunized with human myelin-associated glycoprotein purified from CNS myelin. Three groups of antibodies were identified: IgG antibodies recognizing the polypeptide moiety and IgG and IgM antibodies recognizing the carbohydrate moiety of the intact molecule. Properties of these antibodies were examined with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the immunostaining technique using human CNS and peripheral nerve myelin, and ganglioside fractions isolated from human brain and peripheral nerve, and with immunohistochemical staining of human peripheral nerves. Part of human peripheral blood mononuclear cells was stained with the antibodies against the carbohydrate moiety, but not with IgG antibodies recognizing the polypeptide moiety. Natural killer activity was partially reduced after treatment of human peripheral blood lymphocytes with an IgM antibody and complement in vitro. The possibility that anti-myelin-associated glycoprotein antibodies might play a role in the pathogenesis of demyelinating diseases through modification of natural killer activity is discussed.

Protein p38: an integral membrane protein specific for small vesicles of neurons and neuroendocrine cells

An intrinsic membrane protein of brain synaptic vesicles with Mr 38,000 (p38, synaptophysin) has recently been partially characterized (Jahn, R., W. Schiebler, C. Ouimet, and P. Greengard, 1985, Proc. Natl. Acad. Sci. USA, 83:4137-4141; Wiedenmann, B., and W. W. Franke, 1985, Cell, 41:1017-1028). We have now studied the presence of p38 in a variety of tissues by light and electron microscopy immunocytochemistry and by immunochemistry. Our results indicate that, within the nervous system, p38, like the neuron-specific phosphoprotein synapsin I, is present in virtually all nerve terminals and is selectively associated with small synaptic vesicles (SSVs). No p38 was detectable on large dense-core vesicles (LDCVs). p38 and synapsin I were found to be present in similar concentrations throughout the brain. Outside the nervous system, p38 was found in a variety of neuroendocrine cells, but not in any other cell type. In neuroendocrine cells p38 was localized on a pleiomorphic population of small, smooth-surfaced vesicles, which were interspersed among secretory granules and concentrated in the Golgi area, but not on the secretory granules themselves. Immunoblot analysis of endocrine tissues and cell lines revealed a band with a mobility slightly different from that of neuronal p38. This difference was attributable to a difference in glycosylation. The finding that p38, like synapsin I, is a component of SSVs of virtually all neurons, but not of LDCVs, supports the idea that SSVs and LDCVs are organelles of two distinct pathways for regulated neuronal secretion. In addition, our results indicate the presence in a variety of neuroendocrine cells of an endomembrane system, which is related to SSVs of neurons but is distinct from secretory granules.

Myelin-associated glycoprotein shares an antigenic determinant with a glycoprotein of human melanoma cells

A sulfated 100K-dalton glycoprotein has been shown to be released into the culture medium of melanoma cells. Monoclonal antibodies 10C5 and 11B5, which were raised to human melanoma cells, as well as HNK-1 bind to this glycoprotein. It is shown here that mouse anti-myelin-associated glycoprotein (MAG) carbohydrate antibodies raised to human MAG and a human IgM paraprotein associated with neuropathy also bind to the same 100K molecule. However, anti-MAG antibodies recognizing peptide epitopes do not appear to react with this glycoprotein of melanoma cells, a result suggesting that its similarity to MAG is restricted to shared carbohydrate moieties. The anti-melanoma antibodies (10C5 and 11B5) resemble HNK-1 in binding to MAG and to some 19-28K-dalton glycoproteins and sulfated, glucuronic acid-containing sphingoglycolipids of the peripheral nervous system (PNS). In addition, the anti-melanoma antibodies cross-react with neural cell adhesion molecule (N-CAM), an observation emphasizing the shared antigenicity between MAG and other adhesion molecules. The results demonstrate that the anti-melanoma antibodies fall into a class of monoclonal antibodies (including HNK-1, human IgM paraproteins associated with neuropathy, anti-human MAG antibodies, and L2 antibodies) that are characterized by reactivity against related carbohydrate determinants shared by human MAG, N-CAM, and several protein and lipid glycoconjugates of the PNS.

A novel family of human major histocompatibility complex-related genes not mapping to chromosome 6

Thymocyte antigens CD1 [Thy,gp45,12] are thought to be the human counterparts of mouse thymus leukaemia (TL) antigens. Serological and biochemical analyses indicate that at least three subsets exist, the first of which (HTA 1/T6) was initially identified by the monoclonal antibody NA1/34. Like TL, CD1 are expressed on cortical thymocytes as well as on some lymphoid neoplasias, and resemble in structure major histocompatibility complex (MHC) class I antigens. However HTA 1/T6 is loosely associated with beta 2-microglobulin and is also found linked by a disulphide bridge to CD8(T8). A molecular genetic approach is needed to investigate the CD1 system, to clarify its relationship to TL antigens and to understand its regulation. We report the isolation of complementary DNA (cDNA) clones encoding a CD1 antigen. These clones reveal a novel family of genes which are MHC-related but are neither equivalent to mouse TL antigens nor linked to the MHC.

Subunit structure of a cortical granule lectin involved in the block to polyspermy in Xenopus laevis eggs

The cortical granule lectin of Xenopus laevis eggs is a large molecular mass glycoprotein involved in the post-fertilization block to polyspermy. We have investigated the subunit structure of this lectin and found that the native molecule contains 10-12 monomers, each of which has considerable charge and size heterogeneity due to glycosylated side chains. In addition, significant amino acid sequence homology is indicated by peptide mapping of subunits separated by isoelectric focusing.

Schistosoma mansoni shares a protective oligosaccharide epitope with freshwater and marine snails

The expression of similar antigenic determinants by trematode parasites and their intermediate (invertebrate) or definitive (vertebrate) hosts has been previously reported. Studies of experimental and human infection by the parasite Schistosoma mansoni have revealed the strong immunogenicity of a surface antigen with a relative molecular mass (Mr) 38,000 (38K). Here we provide evidence that the important protective epitope of the 38K molecule is expressed by the uninfected intermediate host of S. mansoni, Biomphalaria glabrata and is synthesized both by the mollusc and by the parasite throughout its life cycle, thus confirming our original hypothesis. Deglycosylation experiments indicate that the protective epitope is an oligosaccharide and in B. glabrata, is associated with a 90K component. Analysis of soluble extracts from different freshwater mollusc species shows that the same protective epitope is found in schistosome as well as in non-schistosome hosts. Moreover, it was also found on the haemocyanin of the keyhole limpet (Megathura crenulata), a carrier protein widely used in immunological studies.

MRC OX-45 antigen: a leucocyte/endothelium rat membrane glycoprotein of 45,000 molecular weight

Monoclonal antibodies MRC OX-45 and OX-46 detect identical or juxtaposed antigenic determinants on a novel rat membrane molecule that plays a possible role in macrophage suppression of antigen-induced T-cell responses. These antibodies react with most mature hematopoietic cells and their bone-marrow precursors, vascular endothelium and some connective tissue. The OX-45 antigens were purified from brain (mainly endothelium) and spleen by immunoaffinity chromatography, and were found to be glycoproteins with apparent Mr 43,000 and 45,000, respectively, as determined by SDS-PAGE analysis. The amino acid compositions of the two preparations were very similar but with no distinguishing features. The broad pattern of distribution was not the result of fortuitous cross-reaction of the MAbs as a single N-terminal sequence was obtained from mixed spleen populations of cells. Carbohydrate compositions of the brain and spleen molecules differed both in absolute amount (22 and 41% by weight, respectively) and in the ratios of various saccharides reflecting overall differences in the patterns of glycosylation between the two tissues. MRC OX-45 IgG showed an heterogeneity in the Mr of its H chain due to the attachment, in some molecules, of carbohydrate structures to the Fd fragment.

Action of trifluoromethanesulfonic acid on highly glycosylated regions of human bronchial mucins

Highly glycosylated glycopeptides were prepared from human bronchial mucus. They were heterogeneous and contained an average of 45 residues of glycosylated hydroxyamino acid per 100 amino acid residues. The kinetics of deglycosylation of these glycopeptides by trifluoromethanesulfonic acid-anisole mixtures at 25 degrees was monitored by chemical analysis and by polyacrylamide gel electrophoresis. The peripheral sugars were almost completely cleaved in 45 min with 3:2 and 2:1 CF3SO3H-anisole. A maximum of 75% of the O-linked N-acetylgalactosamine residues were released and mixtures of glycopeptides and peptides were obtained. Increasing the reaction time caused peptide bond cleavage. Rather mild conditions (1.2:1 CF3SO3H-anisole at 25 degrees for 90 min) gave limited deglycosylation of highly glycosylated bronchial glycopeptides, allowing the uncovering of GalNAc-peptide linkages and peptide regions able to induce the formation of specific antibodies in the rabbit.

Biosynthesis and intracellular processing of carbonic anhydrase in Chlamydomonas reinhardtii

Carbonic anhydrase (CA) of Chlamydomonas reinhardtii is a glycoprotein of 35 kDa which is localized outside the plasma membrane. The activity of CA was increased when the CO2 concentration during photoautotrophic growth was decreased to air level. After decreasing the CO2 concentration from 4% to 0.04%, several polypeptides including CA were induced continuously or transiently. To investigate the biosynthesis and intracellular processing of CA, the cells of wall-less mutant CW-15, which secretes CA into the culture medium, were pulse-labeled with radioactive arginine, chased, and radioactive proteins were immunoprecipitated with anti-CA serum. A 42-kDa polypeptide with isoelectric point (pI) of 7.1-7.3 was first synthesized. Within 5 min the molecular mass of this polypeptide was decreased to 35 kDa and it was then secreted into the culture medium within 30 min. This indicates that the former is the precursor form and the latter the mature form of CA. The primary translation product from poly(A)-rich RNA in a cell-free reticulocyte lysate system from a rabbit was a 38-kDa polypeptide. This was cotranslationally converted into the 42-kDa precursor in vitro in the presence of dog pancreatic microsomal membranes. As the 42-kDa precursor had a high affinity to concanavalin A, it was assumed to have a high-mannose-type oligosaccharide. The mature enzyme had a pI of 6.1-6.2 and was composed of more than two isoforms, which had a complex-type oligosaccharide with low affinity to concanavalin A. Chemical deglycosylation of the mature enzyme by trifluoromethanesulfonic acid indicated that the molecular mass of the polypeptide moiety was 32 kDa and the difference between this and the primary translation product suggests that cleavage of the polypeptide occurs during its biosynthesis.

A structural analysis of the carbohydrate side chains on class I and class II histocompatibility antigens of the swine facilitated by heteroantisera specific for the denatured polypeptides

Rabbit heteroantisera specific for the denatured glycoprotein subunits of swine class I and class II major histocompatibility complex (MHC) antigens have been prepared and utilized to monitor changes in the mobilities of these polypeptides on SDS-polyacrylamide gel electrophoresis subsequent to various deglycosylation procedures. This information, in combination with lectin reactivity patterns for the glycoproteins bound to nitrocellulose, has made it possible to define specific structural features of the MHC antigen-associated carbohydrate side chains. Both the class I heavy (alpha) chain and the class II light (beta) chain bear a single, N-linked, complex-type oligosaccharide which reacts with lentil lectin (LcH), but not concanavalin A (Con A); a reactivity pattern suggesting the possibility of a special triantennary structure. In contrast, the class II heavy (alpha) chains appear to possess two carbohydrate units, one an N-linked, LcH-reactive, complex-type side chain, and the other, an N-linked, Con A-reactive, high-mannose-type of oligosaccharide. The data suggest considerable homology between the swine and human MHC antigens with respect to the structure of their carbohydrate side chains. The analysis also serves to illustrate how antibodies specific for the denatured polypeptide backbone of individual glycoproteins, along with lectin reactivity patterns, can be used to extract structural information about the attached carbohydrate moieties using minimal amounts of partially purified glycoproteins.

Exposure of binding sites for antibodies and concanavalin A on collagen by solubilization in hot urea. An immunoblot analysis

The presence of urea during solubilization of collagenous samples for SDS PAGE had a marked effect upon mobility of collagenous polypeptides and upon binding of antibodies from certain rabbit antisera, antibodies from several human sera and binding of concanavalin A. When samples were solubilized with urea by heating at 100 degrees C the mobility of collagenous polypeptides was retarded relative to samples that had been heated without urea or exposed to urea without heating. Antibodies from the rabbit sera only bound on immunoblots to collagen that had been urea/heat-treated. Periodate oxidation and deglycosylation with trifluoromethanesulfonic acid abolished binding of the rabbit antibodies. The results indicate the presence of carbohydrate epitopes buried within collagenous polypeptides that are exposed by harsh denaturing conditions. Heating with urea appears to cause an unfolding of collagenous molecules beyond that produced by SDS solubilization without urea. These results underscore the necessity to pay close attention to conditions used to solubilize for electrophoresis samples that are subsequently used as targets for antibodies or other ligands.

Biosynthesis, processing and secretion of mucus glycoprotein in the rat stomach

For the study of the biosynthesis, processing and secretion of mucus glycoproteins in rat gastric mucous cells, antibodies were raised against purified gastric mucus glycoproteins and against deglycosylated gastric mucus glycoproteins. Indirect immunofluorescence analysis of gastric mucosa sections revealed that both antibodies specifically labelled the mucus glycoprotein-synthesizing cells in the gastric mucosa. Stomach segments were pulse-labelled with [35S]cysteine and chased for various times. The radioactively labelled (glyco)proteins were quantitatively immunoprecipitated and analyzed by SDS-polyacrylamide gel electrophoresis. Less than 3% of the total radioactivity incorporated in protein was found to be present in mucus glycoproteins. Antibodies raised against native mucus glycoproteins recognized only high-molecular-weight mucus glycoproteins, while the antibodies against deglycosylated glycoproteins also bound to probable precursor forms. The synthesis of mature mucus glycoproteins (Mr greater than 300 000) required about 90 min. After 3 h of chase, only a small portion of the pulse-labelled mucus glycoproteins had been secreted; the majority of the radioactive glycoproteins at that time was still associated with the tissue. Immature (glyco)proteins were not secreted into the medium.

Isolation and characterization of lecithin-cholesterol acyltransferase from hog plasma

Lecithin-cholesterol acyltransferase (EC 2.3.1.43) was purified from hog plasma by a highly efficient procedure. The final enzyme preparation was purified 30,000-fold over the starting material and was homogeneous as indicated by polyacrylamide gel electrophoreses in the presence of both SDS and urea. The purified hog lecithin-cholesterol acyltransferase had an apparent molecular weight of 66 000 on SDS-polyacrylamide gel electrophoresis and HPLC and was found to contain about 21.4% (w/w) carbohydrate-hexose, 11.3%; hexosamine, 1.9%; sialic acid, 8.2%. The amino acid composition analysis showed that hog lecithin-cholesterol acyltransferase contains four half cystines per mol; two cysteines were titrated at neutral pH with 5,5'-dithiobis(2-nitrobenzoic acid). Nearly all the phenolic groups were unavailable to the solvent at neutral pH, while they become exposed at around pH 11. Hog lecithin-cholesterol acyltransferase was found to be associated with HDL in the plasma and it prefers HDL as a substrate. The physicochemical properties of hog lecithin-cholesterol acyltransferase were generally similar to those of the human and the rat enzyme.

Partial characterization of an allergenic glycoprotein from peanut (Arachis hypogaea L.)

A concanavalin A-reactive glycoprotein allergen has been isolated from peanut (Arachis hypogaea). The allergen was separated by affinity chromatography and purified by gel permeation and ion-exchange chromatography. The monomeric molecular weight is 65,000 and the pI is 4.6. The presence of one cysteine residue per molecule results in some dimer formation. Concanavalin A-reactive glycoprotein is a potent allergen for peanut-sensitive patients in both in vivo and in vitro tests. It is allergenically stable, on in vitro examination, at temperatures of up to 100 degrees C and over the pH range 2.8-10. Removal of the carbohydrate moiety failed to eliminate the allergenicity. Concanavalin A-reactive glycoprotein is identified in the crossed immunoelectrophoretic pattern as a major antigen of peanut protein extract but its structural characteristics indicate that it is probably not a component of the major storage-protein complex, arachin.

The solution structure of mucous glycoproteins: proton NMR studies of native and modified ovine submaxillary mucin

The solution structure of native and systematically modified ovine submaxillary mucin (OSM) has been probed by proton NMR spectroscopic methods. Most of the resonances in the spectra have been tentatively assigned to the peptide and O-linked disaccharide, alpha-N-acetylneuraminic acid 2----6 alpha-N-acetylgalactosamine protons. On the basis of the observed chemical shifts, spectral resolution, and behavior of the exchangeable protons it is concluded the mucin possesses internal segmental flexibility and exists in solution as a random coil peptide. No long-lived interresidue peptide or carbohydrate hydrogen bonds were detected. The removal of (i) the C8 and C9 carbons of the sialic acid residue, (ii) the entire sialic acid residue, and (iii) the complete disaccharide side chain resulted in no significant changes in peptide core conformation. A limited set of proton spin coupling constants and nuclear Overhauser enhancements has been obtained for the threonine glycopeptide side chains in native and modified mucin. The results are consistent with the previously reported conformations for the (1----6) linkage in oligosaccharides and the threonyl glycosidic linkage in glycopeptides. The OSM disaccharide may exist as a extended linear structure with rotational freedom about the GalNAc C5-C6 bond, while the threonine glycosidic linkage appears to be sterically constrained, although multiple conformations about the threonine C beta-O gamma bond may be allowed. The small chemical shift perturbations detected in the glycosylated threonine methyl protons and the GalNAc carbons upon removal of the terminal sialic acid residue are consistent with this model.

Posttranslational processing of secretory component in the rat jejunum by a brush border metalloprotease

Secretory component (SC) is a glycoprotein that mediates the transcellular transport of polymeric immunoglobulins into external secretions. SC is synthesized and inserted into the plasma membrane of epithelial cells and hepatocytes as a transmembrane protein, where it serves as a receptor for polymeric immunoglobulins. SC is posttranslationally cleaved to a soluble protein before secretion into external fluids. In the rat jejunum, we observed that the molecular weights of both the major membrane and soluble forms of SC were 10,000-20,000 smaller than the comparable hepatic forms of the glycoprotein. We therefore set out to determine the reason for the differences in size of SC between these two tissues. The smaller size of jejunal SC was not due to the action of pancreatic proteases or differential glycosylation but was due to proteolysis by a jejunal brush border protease. The protease was characterized as a metalloprotease, with a pH optimum of approximately 5. It is present in jejunal, ileal, and renal tubular brush borders as an integral membrane constituent. When the protease was inhibited in vivo, conversion of jejunal secretory component to the smaller size was partially prevented. Thus, in the rat jejunum, SC undergoes two posttranslational proteolytic events: conversion of membrane secretory component to the soluble form and conversion of soluble SC to a smaller size by a previously undescribed brush border protease.

Radiation inactivation of human intestinal mucin: determination of the size of the functional antigenic unit

Previously we have shown that the major antigenic determinant of human intestinal mucin is associated with its glycopeptide monomers and not the 118 kDa 'link' component. In the present study, the size and nature of the functional unit containing the antigenic determinant has been assessed by radiation inactivation and immunological assays. Increasing doses of radiation led to a monoexponential decay in antigenic reactivity due to a progressive loss of antigenic determinants. From three independent mucin preparations, a value of 78500 +/- 7000 was determined for the Mr of the functional antigenic unit. Prolonged pronase digestion of native mucin released large degraded glycopeptide monomers containing all the mucin carbohydrate, and low molecular weight peptides. The antigenicity of the glycopeptides decreased with digestion but could not be recovered in the peptide fractions, suggesting that determinants were released and destroyed by the enzyme. Treatment of native mucin with trifluoromethanesulphonic acid caused a major loss of carbohydrate (approx. 70%), but the protein component was unchanged in amino acid profile and remained antigenic. Subsequent thiol reduction, however, abolished the antigenicity of the deglycosylated mucin. We conclude that antigenicity is associated with a non-glycosylated segment of the peptide backbone of the glycopeptides and that a large functional unit of Mr 78500 which is stabilized by disulphide bonds is important for full antigenic activity.

Unusual phylogenetic conservation of the N-terminal amino acid sequence of the central nervous system-specific membrane glycoprotein F3-87-8 (CNSgp130)

CNSgp130 is a CNS-specific membrane glycoprotein abundantly expressed throughout the mature mammalian CNS. The molecule is recognised by the mouse monoclonal antibody F3-87-8, which reacts with a determinant of CNSgp130 common to all mammals tested to date. Rat and human CNSgp130 were purified by a combination of F3-87-8 monoclonal antibody affinity and gel permeation chromatography, and the N-terminal amino acid sequence was determined by gas-phase sequencing techniques. The results show a remarkable conservation of the N terminus of the CNSgp130 polypeptide between rats and humans, with complete identity of the first 20 amino acid residues. There was an unusually high and phylogenetically conserved number of cysteines in this region. The sequence showed no homology to other known sequences and should prove useful in precisely identifying the relationship of CNSgp130 to other CNS membrane molecules.

Nature of the mouse egg's receptor for sperm

The zona pellucida is an extracellular coat that surrounds all mammalian eggs. Sperm must penetrate the zona pellucida in order to reach and fuse with the plasma membrane of unfertilized eggs. Penetration is accomplished by a sequence of events involving both egg and sperm. First, sperm must bind to the outer margin of the zona pellucida. Such binding is mediated in a relatively species-specific manner by "sperm receptors" in the zona pellucida. Second, sperm must undergo the "acrosome reaction", a membrane fusion event, in order to traverse the zona pellucida. Here we review results from our own laboratory which demonstrate that, during the course of sperm-egg interaction in mice, zona pellucida glycoprotein ZP3 serves as both receptor for sperm and inducer of the acrosome reaction. Furthermore, we review evidence from our laboratory indicating that the sperm receptor activity of ZP3 is dependent only on its 0-linked carbohydrate components, whereas acrosome reaction-inducing activity is dependent on the polypeptide portion of ZP3 as well.

The importance of disulfide bridges in human endopeptidase (enkephalinase) after proteolytic cleavage

The neutral endopeptidase (NEP) is a membrane-bound enzyme, which is solubilized by treatment with the protease, papain. Papain did not affect the apparent catalytic activity or the molecular mass of the purified human enzyme in SDS-PAGE. When NEP was treated with a reducing agent after papain digestion, it dissociated into smaller, lower molecular mass fragments. Amino acid analysis and s-carboxymethylation of the half cystine residues indicated that NEP contains four S-S bridges. We concluded that, although covalent bonds appear to be cleaved in NEP by papain, its activity and structure are sustained by S-S bridges.

Molecular expression of xylanase gene in Cryptococcus albidus

In the yeast Cryptococcus albidus, the utilization of xylan as compared to xylose requires at least an inducible endoxylanase enzyme, secreted in the culture medium. The endoxylanase induction was monitored by immunoprecipitation of in vivo and in vitro synthesized products. The mature endoxylanase is a highly glycosylated enzyme with an apparent molecular weight of 48 000. Upon chemical deglycosylation with trifluoromethanesulfonic acid, the molecular weight was reduced to 40 000. Addition of tunicamycin to the culture medium resulted in the synthesis of a modified polypeptide having a molecular weight of 40 000. Poly(A)-containing RNA isolated from the yeast was translated in the rabbit reticulocyte protein-synthesizing system. The appearance of a translatable xylanase mRNA was observed in xylan-grown cells but not in xylose-grown cells. The polypeptide identified as xylanase had a molecular weight of 44 000. This suggests that the xylanase is synthesized as a precursor, containing a peptide signal sequence of 35 residues.

The origin of human cartilage proteoglycan link-protein heterogeneity and fragmentation during aging

Human articular-cartilage link proteins are resolved into three components by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, indicative of three different structures. The action of the proteinase clostripain yields a single link-protein component with electrophoretic properties analogous to those of the smallest (most mobile) native link protein, suggesting that this link protein may be derived naturally from one or both of the larger molecules by proteolytic cleavage in situ. Upon chemical deglycosylation of native link protein two components are resolved, suggesting that two of the link proteins differ only in their degree and/or type of oligosaccharide substitution. This pattern is compatible with a proteolytic origin for the smallest link protein. During aging further proteolytic fragmentation occurs, though it is only apparent on reduction of disulphide bonds. This fragmentation occurs at identical sites in all three native link proteins, indicating the existence of a large region common to all the link proteins, which appears to consist predominantly of the C-terminal half of the molecules. These observations are compatible with the variation in oligosaccharide and proteolytic heterogeneity occurring at the N-terminus of the link proteins.

Purification and characterization of a basic lysophospholipase in germinating barley

Lysophospholipase from germinating barley seeds has been isolated using methods which take advantage of the fact that the activity is basic, lipophilic, and contains carbohydrate. There appears to be at least three enzymatic forms of the activity, two with molecular weights at 40,000 and one at 41,000. They comigrate with a pI of 8.8 on isoelectric focusing and they all undergo deglycosylation to give a polypeptide with molecular weight 36,000, indicating 10 to 12% carbohydrate in the original glycoproteins. The enzyme is inactivated by sulfhydryl reagents and has a tendency to aggregate. The latter property may be attenuated with mercaptoethanol with which the activity is stable for more than 3 months at 4 degrees C. The most active barley enzyme has a Km of 30 microM for lysophosphatidylcholine and a Vmax, 200 mumol/min/mg. The specific activity is 20 times greater than that for lysophospholipases isolated from animal sources. It has no phospholipase, lipase, or transacylase activity. It is most active on lysophosphatidylcholine with a saturated 16 carbon or unsaturated 18 carbon chain; these are the predominant molecular species of lysophospholipid present as inclusion complexes in barley starch. The role of the barley lysophospholipases in barley germination is discussed.

Inheritance and biochemical analysis of four electrophoretic variants of β-conglycinin from soybean

Three genes which code for variant β-conglycinin subunits were identified. Alleles Cgy 1 (S) and Cgy 2 (S) were codominant with Cgy 1 and Cgy 2 and produced α' and α subunits, respectively, with reduced electrophoretic mobility. Allele Cgy 3 (D) increased the mobility of at least one polypeptide in the β subunit family and exhibited incomplete dominance. Gene loci Cgy 2/Cgy 2 (S) and Cgy 3 (D) /cgy 3 (D) were linked, whereas Cgy 1/Cgy 1 (S) / cgy 1 segregated independently of the others. Techniques developed for purification of normal β-conglycinin subunits were effective in purifying the altered subunits. Deglycosylated variant proteins from seeds containing the alleles Cgy 1 (S) , Cgy 2 (S) , or Cgy 3 (D) also has altered mobility relative to deglycosylated normal proteins. Therefore, the altered subunits contained changes in their amino acid sequences rather than in their carbohydrate moieties. This interpretation is consistent with the observed codominant or incompletely dominant mode of inheritance for these alleles and suggests that each contains an altered nucleotide sequence in the structural gene. A fourth variant, which exhibited doublet α' and a electrophoretic bands, was inherited in a recessive fashion. Deglycosylated subunit proteins from this variant were identical in electrophoretic mobility to those of the deglycosylated normal protein. This suggests that the doublet phenotype resulted from an alteration in the carbohydrate moiety of these subunits. The gene or genes which condition this variant presumably are required for normal post-translational modification of the subunit carbohydrates and as such may be useful for investigating these events.

Covalently bound wall proteins of pollen grains and pollen tubes grown in vitro and in styles after self- and cross-pollination in Lilium longiflorum

A method was worked out using trifluoromethanesulfonic acid (TFMS) as a reagent to split the covalently bound proteins, which are NaCl insoluble, from pollen tube walls of Lilium longiflorum, leaving the peptide bonds essentially intact. After electrophoretic separation, comparisons were made among these proteins from pollen grains and pollen tubes grown in vitro and in styles after self- and cross-pollination. It was found that a) the patterns of covalently bound wall proteins were different between tubes grown in vitro and in vivo; b) fewer bands were found in covalently bound wall proteins than that in noncovalently bound proteins; c) the bands remained almost the same no matter whether the tubes had been cross pollinated or self pollinated, indicating that while the noncovalently bound proteins were involved in incompatibility as shown in the previous paper, the covalently bound proteins may only serve as a structural component, having little to do with incompatibility.

Circular dichroism and fluorescence spectroscopic analyses of a proline-rich glycoprotein from human parotid saliva

A proline-rich glycoprotein (PRG) was isolated from human parotid saliva and examined by circular dichroism and fluorescence spectroscopy. Addition of guanidine hydrochloride to PRG labeled with an extrinsic dansyl probe had no effect on the fluorescence spectra's 511 nm lambda-max location. Thermodynamic calculations supported the contention that PRG has no significant tertiary structure. Circular dichroism results for PRG were simulated by computer and a secondary structure composed of 70% random coil and 30% beta-form conformation was predicted. Circular dichroism of PRG failed to detect either poly-L-proline type I or II structures. Deglycosylation of PRG had no measurable effect on the circular dichroism spectrum, indicating that the carbohydrate side chains had little influence on PRG secondary structure. Based upon mathematical calculations, beta-turns were predicted around three glycosylated Asn residues of PRG. These collective data suggest that PRG is composed of a disordered polypeptide chain with at least three of the N-linked Asn residues participating in some type of beta-turn.

Alkaline phosphatase and 5'-nucleotide phosphodiesterase from bovine intestine are cross-reactive

Polyclonal antibodies to native alkaline phosphatase and to native 5'-nucleotide phosphodiesterase were found to strongly cross-react with both enzymes. The antibodies also cross-react with both denatured enzymes, with glycopeptides from 5'-nucleotide phosphodiesterase, and with the oligosaccharides remaining after Pronase E digestion of the phosphodiesterase. They do not cross-react with either enzyme after their oligosaccharides have been modified or removed by periodate or trifluoromethanesulfonic acid treatment. Antibodies to denatured 5'-nucleotide phosphodiesterase do not bind to the native phosphodiesterase or alkaline phosphatase but do cross-react with denatured alkaline phosphatase even after removal or modification of the carbohydrate moieties. These results suggest that antibodies to denatured 5'-nucleotide phosphodiesterase may recognize amino acid sequence homology between alkaline phosphatase and 5'-nucleotide phosphodiesterase. However, antibodies to native enzymes apparently recognize cross-reactive determinants of the native enzymes which are carbohydrate in nature. This is the first report of antimammalian alkaline phosphatase antibodies which recognize the carbohydrate moieties of the enzyme.

Glycoproteins of the chromaffin-granule matrix: use of lectin blotting to distinguish several separate classes

The soluble proteins released by hypotonic lysis of highly purified bovine adrenal chromaffin granules were analysed by one- and two-dimensional electrophoresis, followed by transfer to nitrocellulose and decoration with lectins or specific antibodies. The effects of neuraminidase treatment, and of chemical deglycosylation by trifluoromethanesulphonic acid, were investigated. It was shown that lectins could be used to distinguish the two major series of chromogranins from each other, from dopamine beta-hydroxylase and from several minor, unidentified glycoprotein components of the lysate. Antibody decoration revealed a complex series of peptides containing enkephalin sequences, some of which changed their electrophoretic mobility on treatment with trifluoromethanesulphonic acid.

Deglycosylation of alpha 1-proteinase inhibitor by endo-beta-N-acetylglucosaminidase F

The glycosidase endo-beta-N-acetylglucosaminidase F (endo F) from Flavobacterium meningosepticum was used for the deglycosylation of rat alpha 1-proteinase inhibitor (alpha 1 PI). alpha 1 PI containing three oligosaccharide side chains of the complex type was isolated from rat serum or from the medium of rat hepatocyte primary cultures. High-mannose-type alpha 1 PI or hybrid-type alpha 1 PI was isolated from the media of hepatocytes treated with 1-deoxymannojirimycin or swainsonine, respectively. The susceptibility of complex-type alpha 1 PI to endo F was studied in the presence of various detergents. 3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate and octyl glucopyranoside turned out to be most effective. In the absence of detergents, digestion of alpha 1 PI with high concentrations of endo F and/or long times of incubation led to the formation of alpha 1 PI with one and two oligosaccharide side chains. In the presence of 0.5% octyl glucopyranoside, the major cleavage products were unglycosylated alpha 1 PI and alpha 1 PI carrying one carbohydrate side chain. In contrast to the complex-type alpha 1 PI, the high-mannose type can be totally deglycosylated by endo F even in the absence of detergents. The susceptibility of the hybrid-type alpha 1 PI to endo F is between that of the complex and the high-mannose types.

Masticatory lubrication. The role of carbohydrate in the lubricating property of a salivary glycoprotein-albumin complex

We report for the first time a masticatory-lubrication assay system to assess the lubricating properties of salivary constituents. The lubricating ability of the proline-rich glycoprotein (PRG) of parotid saliva was enhanced by human serum albumin. The interactive effect of albumin was abolished by chemically deglycosylating the glycoprotein. Fluorescence spectroscopy with a hydrophobic probe verified the existence of a PRG-albumin complex and demonstrated that deglycosylation of the PRG altered the nature of its interaction with albumin.

A monoclonal antibody to dopamine beta-monooxygenase: detection of biosynthetic intermediates

A monoclonal antibody to dopamine beta-monooxygenase (DBH) has been produced by an in vitro immunization technique. This antibody has been found to react with an epitope common to both soluble DBH (SDBH) and membrane-bound DBH (MDBH). A single CNBr fragment contains this antigenic site. Examination of electrophoretograms of chromaffin granule membrane and lysate by the immunoblot procedure revealed additional complexity. A 58-KDa polypeptide in low abundance was stained which could not be detected with the polyclonal antiserum. Chemical deglycosylation of SDBH produces two new polypeptides of 67 and 58 KDa. The entirety of this data suggests that the 58-KDa band is an unglycosylated form of DBH, proteolytically cleaved after biosynthesis.

Characterization of insulin receptor carbohydrate by comparison of chemical and enzymatic deglycosylation

To characterize the carbohydrate moieties of the insulin receptor on IM-9 lymphocytes, the cells were surface iodinated and solubilized, and the insulin receptors were precipitated with anti-receptor antibody. The precipitates were resuspended, subjected to either enzymatic digestion or chemical treatment with trifluoromethanesulfonic acid and the relative mobilities of the alpha and beta subunits before and after treatment were analyzed by polyacrylamide gel electrophoresis and autoradiography. The results indicate that the alpha subunit possesses primarily N-linked carbohydrate which is both complex (Endoglycosidase F sensitive) and polymannose (Endoglycosidase H sensitive). The beta subunit also contains polymannose oligosaccharide units and has, in addition, a substantial amount of carbohydrate which is removed by chemical treatment but is not susceptible to Endoglycosidase F, suggesting the presence of O-linked saccharides. The apparent molecular weights of the core protein of the mature alpha and beta subunits as determined by gel electrophoresis following complete deglycosylation are 98 kDa and 80 kDa, respectively.