Monoclonal anti-glycoprotein antibody that blocks cell adhesion in Polysphondylium pallidum

The influence of simple sugars, salts, andBotrytis-specific monoclonal antibodies on the binding of bacteria and yeast to germlings ofBotrytis cinerea

The influence of simple sugars, salts, and Botrytis-specific monoclonal antibodies on the binding of three bacteria (Enterobacter aerogenes Hormaeche & Edwards, Enterobacter cloacae (Jordan) Hormaeche & Edwards, and Ochrobactrum anthropii gen.nov.) and three yeasts (Candida sake (Sarto & Ota) van Uden & Buckley, Candida pulcherrima (Lindner) Windisch, and Trichosporon pullulans (Lindner) Diddens & Lodder) to Botrytis cinerea (Persoon:Fr) was examined. Solutions of 0.1 M D(+)-galactose, L-fucose, or Botrytis-specific monoclonal antibodies significantly reduced populations of E. aerogenes and E. cloacae adhering to pathogen germlings, whereas 0.1 M raffinose significantly reduced C. sake or C. pulcherrima adhesion. In cytochemical studies, lectin-gold labeling demonstrated the presence of galactose moieties in the walls or matrix of E. aerogenes, and this labeling was diminished in bacteria that were attached to B. cinerea. Immunolabeling with a Botrytis-specific monoclonal antibody that recognizes a glycoprotein was particularly intense in condensed regions of the pathogen matrix associated with adherent E. aerogenes, whereas C. sake - B. cinerea interactions revealed a loose encapsulation of adherent yeast cells by the matrix of B. cinerea. Results from this study suggest the presence of several adhesion mechanisms that can be distinguished according to yeast or bacterial binding and further defined according to the genus.Key words: adhesion, bacteria, biocontrol, Botrytis cinerea, ultrastructure, yeast.

Evidence for a glycolipid anchor of gp64, a putative cell-cell adhesion protein of Polysphondylium pallidum

The membrane-bound glycoprotein (gp64) of the cellular slime mold Polysphondylium pallidum, is a putative cell-cell adhesion protein identified by adhesion-blocking antibody fragments. Since gp64 can be purified in a few days and in substantial yields, it is a good candidate for clarifying the structure of a cell-cell adhesion protein. This study reveals that gp64 possesses a glycolipid anchor which is sensitive to deamination but resistant to phosphatidylinositol-specific phospholipase C from Bacillus thuringiensis. Although the anchor resistance to phosphatidylinositol-specific phospholipase C can be ascribed to the presence of an additional acyl chain on the inositol ring in the glycosyl phosphatidylinositol anchors, this was not the case. After a mild-base treatment that released an additional acyl chain on the inositol ring, only a trace amount of fatty acid was detected but, after strong acid hydrolysis, we detected both amide-linked fatty acids and a long-chain base. The long-chain base was further analysed by gas-chromatography/mass spectrometry and was found to be phytosphingosine. Both fatty acids and myo-inositol were also analysed by gas-chromatography/mass spectrometry. These data suggest that gp64 possesses a glycolipid anchor which contains ceramide and myo-inositol.

A purification method and N-glycosylation sites of a 36-cysteine-containing, putative cell/cell adhesion glycoprotein gp64 of the cellular slime mold, Polysphondylium pallidum

A 64-kDa membrane-bound glycoprotein (gp64) of the cellular slime mold Polysphondylium pallidum, is a putative cell/cell adhesion protein identified by adhesion-blocking antibody fragments (Fab). gp64 is expressed on the cell surface of growth-phase cells and seems to mediate cell/cell adhesion. This paper describes an improved purification method based on the lipophilic nature of this protein. A critical step in the purification method is to collect an insoluble top layer appearing during ammonium sulfate precipitation. The sequence of cDNA encoding gp64 and its deduced amino acid sequence have been determined previously. Based on cDNA sequence data, the structure of gp64 protein was analyzed: almost all amino acid compositions and partial amino acid sequences of lysylendopeptidase-digested peptides of gp64 were determined by protein analysis; all six asparagine-linked glycosylation sites (Asn-Xaa-Ser/Thr) in fact contain carbohydrates, and all 36 cysteine residues were involved in forming disulfide bridges. From these data, gp64 seems to be a unique protein among cell/cell adhesion proteins.

An anticarbohydrate monoclonal antibody inhibits cell-cell adhesion in many species of Dictyostelium but not of Polysphondylium

The anticarbohydrate monoclonal antibody d-41 inhibits the adhesion of aggregating cells, as measured by an in vitro assay, in every species of Dictyostelium tested but in none of the species from the genus Polysphondylium. Although d-41 binds significantly to the surface of cells from both genera, the ability to inhibit adhesion correlates with the binding of the antibody to a few, mostly developmentally regulated, membrane-associated proteins in each of the species affected. Previous work in D. discoideum and D. purpureum have shown that the major d-41-b binding proteins from these species at this time in development are directly involved in the adhesion process. Therefore, the presence of the epitope on these proteins in the other species of Dictyostelium implicates them in the adhesion mechanism. The function of the carbohydrates containing the epitope is yet to be determined.

Developmentally regulated cell-cell adhesion in Dictyostelium purpureum is mediated by a glycoprotein synthesized in nonadhesive cells

Upon starvation the cellular slime mold, Dictyostelium purpureum, develops a form of cell-cell adhesion aiding in the formation of large multicellular aggregates, which are capable of further differentiation. The molecule that mediates this adhesion is a glycoprotein of Mr approximately 40,000. The protein shares a common carbohydrate epitope with another well-characterized cell adhesion molecule from Dictyostelium discoideum, contact sites A, but the polypeptides to which it is attached differ for each species. Although mediating a developmental form of adhesiveness, the protein is synthesized in vegetative cells at a time when they do not adhere. Most of the vegetative protein is associated with cell membranes and appears to be on the surface of these cells. The protein is compared to other cell adhesion molecules from other species of cellular slime molds, and possible explanations for its inability to function in vegetative cells are discussed.

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.

Inhibition of development in Myxococcus xanthus by monoclonal antibody 1604

Monoclonal antibody (mAb) 1604 is directed against a cell surface antigen of Myxococcus xanthus. Purified antibody 1604 inhibited development of M. xanthus under conditions of submerged culture procedure otherwise leading to fruiting body formation. Intact molecules of mAb 1604, as well as its Fab fragments, inhibited developmental aggregation, autolysis, fruiting body formation, and sporulation. The addition of relatively small amounts of antibody every 4 hr was much more effective than a single large dose given at the onset of development. The inhibitory action of mAb 1604 on development was reversible after prolonged incubation of the antibody with cells; this was probably due to proteolytic degradation of the antibody. The effect of mAb 1604 on submerged bacterial development was neutralized by affinity-purified 1604 cell surface antigen. Another antibody, mAb 2788, directed against an M. xanthus cell surface antigen, did not block development. These data suggest that 1604 cell surface antigens is involved in contact-mediated cell interactions in M. xanthus.

Monoclonal antibodies to surface glycoconjugates in Chlamydomonas eugametos recognize strain-specific O-methyl sugars

Monoclonal antibodies are described that are directed against cell surface components of the unicellular green alga Chlamydomonas eugametos. These antibodies recognize strain-specific epitopes which occur at the surface of vegetative and gametic cells. Two different groups of epitopes are distinguished that are never detectable together in one clonal cell culture. Evidence is presented showing that the antigenicity of cell surface molecules is a consequence of the presence of particular O-methylated sugars. Monoclonal antibodies reacting with one group of epitopes were studied in more detail, and immunoprecipitation and Western-blot studies showed that these epitopes can be arranged into four classes. The use of these monoclonal antibodies as strain-specific markers in light- and electron-microscopical techniques is illustrated.

A microcyst-overproducing mutant of Polysphondylium pallidum

A mutant, PN6017, of the cellular slime mold Polysphondylium pallidum was selected by cell-surface labeling with a monoclonal antibody, mAb 293, and fluorescence-activated cell sorting. The antibody was directed against an L-fucose-containing epitope on glycoproteins, designated ep 293, and the mutant showed reduced and delayed expression of this epitope. PN6017 was distinguished from other mutants of this kind by extensive microcyst formation on agar plates under conditions where the wild type formed only sparse microcysts. In suspension cultures transformation of cells into microcysts was negligible in the wild type, and close to 100% in the mutant. Under these conditions microcyst formation in the mutant began at 5-7 h of starvation. At the same time expression of ep 293 and also of a developmentally regulated cytoplasmic protein, pallidin, became detectable. This coincidence in time suggests that microcyst formation in PN6017 is coupled to the same control mechanism as the two other developmentally regulated processes.

Cell surface carbohydrates and cell recognition in Dictyostelium

Carbohydrate ligands and complementary receptors have been detected on the surface of Dictyostelium cells, using lectins, monoclonal antibodies, and immobilized sugar probes. They have been implicated in cell recognition processes, such as phagocytosis and intercellular adhesion, and could act as membrane signals for differentiation. Specific glycoproteins have been proposed to mediate intercellular adhesion in Dictyostelium discoideum and Polysphondylium pallidum and to account for the species-specificity of adhesion displayed by these species. Recent studies with the inhibitor of N-glycosylation, tunicamycin, and with glycosylation defective mutants suggest that some carbohydrate groups in these glycoproteins play a role in cell adhesion.

Protein-linked oligosaccharide implicated in cell-cell adhesion in two Dictyostelium species

Monoclonal antibody d-41, previously shown to block in vitro cell-cell adhesion in aggregating Dictyostelium discoideum, also blocks adhesion in aggregating D. purpureum. In both species the antibody reacts with proteins with Mr approximately 80,000, 37,000, and 27,000, presumed to be glycoproteins since the d-41 epitope is destroyed by periodate oxidation but unaffected by extensive Pronase digestion. Polyclonal antibodies raised against the mixture of d-41 reactive glycoproteins that had been purified by immunoaffinity chromatography are potent inhibitors of D. discoideum adhesion, and adhesion-blocking activity is neutralized extensively and equivalently by each of the purified glycoproteins from D. discoideum with which d-41 reacts. In contrast, polyclonal antibodies raised against the same purified glycoproteins after they had been oxidized with periodate do not block cell-cell adhesion although they react with the glycoproteins with Mr approximately 80,000, 37,000, and 27,000 and bind as extensively to the surface of aggregating D. discoideum cells as do the adhesion-blocking polyclonal antibodies. When taken together, these results raise the possibility that some component of the d-41 binding oligosaccharide participates in cell-cell adhesion.

Monoclonal antibodies that block cell adhesion in Polysphondylium pallidum: reaction with L-fucose, a terminal sugar in cell-surface glycoproteins

By permethylation analysis the linkages of L-fucose and D-mannose in the oligosaccharide residues of cell surface glycoproteins of Polysphondylium pallidum were determined. Mannose was found in terminal positions, in 1,2-, 1,3- and 1,6-intra-chain linkages, and at branch points. Fucose was exclusively located at nonreducing ends. Fab of a monoclonal antibody, mAb 293, has been previously shown to inhibit cell adhesion in P. pallidum completely. Binding of this antibody to glycoprotein was blocked by L-fucose, and at very high concentrations also by D-mannose. The dissociation constant for the antibody-fucose complex was Kd = 70 microM, which was two orders of magnitude higher than estimated for the natural oligosaccharide. Antibody-glycoprotein complexes dissociated in the presence of 100 mM L-fucose with a half-time of about 56 s. The blockage by L-fucose is taken as evidence that the adhesion-blocking antibody binds to oligosaccharide end groups containing L-fucose as the terminal sugar.