Bacterial isolation by lectin-modified microengines

New template-based self-propelled gold/nickel/polyaniline/platinum (Au/Ni/PANI/Pt) microtubular engines, functionalized with the Concanavalin A (ConA) lectin bioreceptor, are shown to be extremely useful for the rapid, real-time isolation of Escherichia coli (E. coli) bacteria from fuel-enhanced environmental, food, and clinical samples. These multifunctional microtube engines combine the selective capture of E. coli with the uptake of polymeric drug-carrier particles to provide an attractive motion-based theranostics strategy. Triggered release of the captured bacteria is demonstrated by movement through a low-pH glycine-based dissociation solution. The smaller size of the new polymer-metal microengines offers convenient, direct, and label-free optical visualization of the captured bacteria and discrimination against nontarget cells.

Crystal structure of peanut lectin, a protein with an unusual quaternary structure

The x-ray crystal structure of the tetrameric T-antigen-binding lectin from peanut, M(r) 110,000, has been determined by using the multiple isomorphous replacement method and refined to an R value of 0.218 for 22,155 reflections within the 10- to 2.95-A resolution range. Each subunit has essentially the same characteristic tertiary fold that is found in other legume lectins. The structure, however, exhibits an unusual quaternary arrangement of subunits. Unlike other well-characterized tetrameric proteins with identical subunits, peanut lectin has neither 222 (D2) nor fourfold (C4) symmetry. A noncrystallographic twofold axis relates two halves of the molecule. The two monomers in each half are related by a local twofold axis. The mutual disposition of the axes is such that they do not lead to a closed point group. Furthermore, the structure of peanut lectin demonstrates that differences in subunit arrangement in legume lectins could be due to factors intrinsic to the protein molecule and, contrary to earlier suggestions, are not necessarily caused by interactions involving covalently linked sugar. The structure provides a useful framework for exploring the structural basis and the functional implications of the variability in the subunit arrangement in legume lectins despite all of them having nearly the same subunit structure, and also for investigating the general problem of "open" quaternary assembly in oligomeric proteins.

Intelectin: a novel lipid raft-associated protein in the enterocyte brush border

Intelectin is a mammalian Ca2+-dependent, D-galactosyl-specific lectin expressed in Paneth and goblet cells of the small intestine and proposed to serve a protective role in the innate immune response to parasite infection. In addition, it is structurally identical to the intestinal lactoferrin receptor known to reside in the enterocyte brush border. To clarify this apparent discrepancy with regard to localization, the aim of this work was to study the cellular and subcellular distribution of small intestinal intelectin by immunofluorescence and immunogold electron microscopy. Secretory granules of lysozyme-positive Paneth cells in the bottom of the crypts as well as goblet cells along the crypt-villus axis were intensively labeled with intelectin antibodies, but quantitatively, the major site of intelectin deposition was the enterocyte brush border. This membrane is organized in stable glycolipid-based lipid raft microdomains, and like the divalent lectin galectin-4, intelectin was enriched in microvillar "superrafts", i.e., membranes that resist solubilization with Triton X-100 at 37 degrees C. This strategic localization suggests that the trimeric intelectin, like galectin-4, serves as an organizer and stabilizer of the brush border membrane, preventing loss of digestive enzymes to the gut lumen and protecting the glycolipid microdomains from pathogens.

Molecular basis of non-self recognition by the horseshoe crab tachylectins

The self/non-self discrimination by innate immunity through simple ligands universally expressed both on pathogens and hosts, such as monosaccharides and acetyl group, depends on the density or clustering patterns of the ligands. The specific recognition by the horseshoe crab tachylectins with a propeller-like fold or a propeller-like oligomeric arrangement is reinforced by the short distance between the individual binding sites that interact with pathogen-associated molecular patterns (PAMPs). There is virtually no conformational change in the main or side chains of tachylectins upon binding with the ligands. This low structural flexibility of the propeller structures must be very important for specific interaction with PAMPs. Mammalian lectins, such as mannose-binding lectin and ficolins, trigger complement activation through the lectin pathway in the form of opsonins. However, tachylectins have no effector collagenous domains and no lectin-associated serine proteases found in the mammalian lectins. Furthermore, no complement-like proteins have been found in horseshoe crabs, except for alpha(2)-macroglobulin. The mystery of the molecular mechanism of the scavenging pathway of pathogens in horseshoe crabs remains to be solved.

Functional and structural diversities of C-reactive proteins present in horseshoe crab hemolymph plasma

Limulin, a sialic-acid-binding and phosphorylethanolamine-binding hemagglutinin in the hemolymph plasma of the American horseshoe crab (Limulus polyphemus), is a hemolytic C-reactive protein [Armstrong, P.B., Swarnakar, S., Srimal, S., Misquith, S., Hahn, E.A., Aimes, R. T. & Quigley, J.P. (1996) J. Biol. Chem. 271, 14717-14721]. We have now identified three types of C-reactive protein in the plasma of the Japanese horseshoe crab (Tachypleus tridentatus), based on different affinities against fetuin-agarose and phosphorylethanolamine-agarose determined by quantitative precipitin assays using fetuin and an artificial phosphorylethanolamine-protein conjugate. Partial amino acid sequences of the isolated C-reactive proteins identified homologous proteins which were named Tachypleus tridentatus CRP-1 (tCRP-1), tCRP-2 and tCRP-3, each of which possibly constitute isoprotein mixtures. tCRP-2 and tCRP-3, but not tCRP-1, agglutinated mammalian erythrocytes. tCRP-1, the most abundant C-reative protein in the plasma, exhibited the highest affinity to the phosphorylethanolamine-protein conjugate but lacked both sialic-acid-binding and hemolytic activities. tCRP-2 bound to both fetuin-agarose and phosphorylethanolamine-agarose, and exhibited Ca2+-dependent hemolytic and sialic-acid-binding activities, suggestive of limulin-like properties. Furthermore, tCRP-2 exhibited a higher affinity to colominic acid, a bacterial polysialic acid. By contrast, tCRP-3 shows stronger hemolytic, sialic-acid-binding and hemagglutinating activities than tCRP-2. tCRP-3 has no affinity to phosphorylethanolamine-agarose, phosphorylethanolamine-protein conjugate and colominic acid. This suggests tCRP-3 is a novel hemolytic C-reactive protein lacking a common characteristic of phosphorylethanolamine-agarose binding affinity. Twenty-two clones of tCRPs with different deduced amino acid sequences were obtained by PCR using oligonucleotide primers based on the N-terminal and C-terminal sequences of tCRPs and with templates including genomic DNA and cDNA of hemocytes or hepatopancreas derived from one individual. The translation products of the tCRP clones possess high molecular diversity which falls into three related groups, consistent with classification based on their biological activities. Only tCRP-3 contained a unique hydrophobic nonapeptide sequence that appears in the transmembrane domain of a major histocompatibility complex class I heavy chain of rainbow trout, suggesting the importance of the hydrophobic patch to the hemolytic activity of tCRP-3. The structural and functional diversities of tCRPs provide a good model for studying the properties of innate immunity in invertebrates, which survive without the benefit of acquired immunity.

Structural and electron-microscopic studies of jacalin from jackfruit (Artocarpus integrifolia) show that this lectin is a 65 kDa tetramer

The 133-amino-acid sequences of the alpha-subunit of jacalin (a lectin from Artocarpus integrifolia) and of the slightly larger alpha'-subunit were determined. The alpha'- and alpha-subunits, in the approximate ratio of 1:3, were found to be virtually identical in their primary structures, except for one valine for isoleucine substitution at position 113. Although both alpha'- and alpha-chains were glycosylated, the extent of glycosylation in the alpha'-chain was much greater than that in the alpha-subunit. In the alpha'-polypeptide, all molecules contained an N-linked oligosaccharide at position 74 and some contained sugar at position 43. The alpha- and alpha'-subunits were found to be strongly non-covalently associated with three distinct beta-subunits containing 20 amino acids each. Electron-microscopic visualization of native jacalin disclosed a structure composed of four alpha-type subunits with a clear-cut 4-fold symmetry. Analytical-ultracentrifugation studies of jacalin revealed an average molecular mass of 65 kDa, a value compatible with a tetrameric structure of the alpha(alpha')-subunits. The recalculated number of sugar-binding sites per jacalin molecule, given a molecular mass of 65 kDa, would yield 0.8 sites per alpha(alpha')-promoter, i.e. about twice the value previously determined [Appukutan & Basu (1985) FEBS Lett. 180, 331-334; Ahmed & Chatterjee (1989) J. Biol. Chem. 264, 9365-9372].

Changes in expression of the endogenous beta-galactoside-binding 14-kDa lectin of chick embryonic skin during epidermal differentiation

Changes in the expression pattern of the gene for the endogenous beta-galactoside-binding 14-kDa lectin of chick embryo were examined immunohistochemically during epidermal differentiation in vivo and in vitro with special reference to detailed localization of the 14-kDa lectin. The gene expression was visualized by the HRP-staining method following in situ hybridization, in which sulfonated cDNA was employed as a probe. The 14-kDa lectin gene expression (mRNA) was detected mainly in the intermediate layer of the epidermis: it was faint in 13-day-old embryos, gradually increased in intensity during epidermal differentiation, and became intensely positive in 17-day-old embryo. The expression of the gene in skin explants was suppressed by vitamin A, which induces mucous metaplasia of the epidermis in vitro. The anti-14-kDa lectin reaction was positive mainly in the intermediate layer of the differentiating epidermis, coinciding chronologically with expression of the gene at the light microscopic level. Immunoelectron microscopy revealed that the positive reaction was primarily localized in desmosomes, in tonofilament bundles anchored to the desmosomes, along the outer surface of the plasma membrane, and in the intercellular space. Essentially the same staining pattern was observed in differentiating epidermis in vitro. The positive reaction was markedly reduced in the epidermis in which differentiation had been suppressed in vitro by the addition of vitamin A.

Purification, subunit characterization and ultrastructure of three soluble bovine lectins: conglutinin, mannose-binding protein and the pentraxin serum amyloid P-component

Conglutinin and mannose-binding protein (MBP) are members of the C-type lectins which are widely present in mammalian plasma. Serum amyloid P-component (SAP) is a member of the pentraxin family with lectin properties. A scheme for the partial purification of all three lectins by carbohydrate affinity chromatography and selective elution was developed. The purification was monitored by SDS-PAGE, Western blotting and electron microscopy. Binding of the lectins to Sephadex-iC3b, their collagenase sensitivity, and the size and antibody reactivity of their subunits was investigated. The demonstration, by SDS-PAGE, of 25-kDa subunits, which were unaffected by collagenase treatment but bound to Sephadex-iC3b and antibodies to human SAP, indicated the existence of bovine SAP. Bovine conglutinin (BK) also showed calcium-dependent binding to Sephadex-iC3b, whereas bovine MBP did not. The binding of BK was inhibitable with GlcNAc. A 3000-fold increase in BK activity (ELISA) was obtained in eluates from Sephadex-iC3b. SDS-PAGE analyses of BK and MBP revealed subunits with an Mr of 43 kDa and 30 kDa, respectively. These subunits were sensitive to collagenase treatment which reduced the Mr to 20 kDa. Electron micrographs revealed a prominent flexible tetramer molecule (diameter 96 nm) in the BK preparations, a predominantly hexameric structure (diameter 30 nm) in the MBP preparations, and single annular pentameric disc-like molecules (diameter 11 nm) in the SAP preparations.

Fabry disease: ultrastructural lectin histochemical analyses of lysosomal deposits

Fabry disease is an X-linked inborn error of glycosphingolipid catabolism resulting from a deficiency of lysosomal alpha-galactosidase activity. Globotriaosylceramide accumulates predominantly in lysosomes of various tissues. Former studies have clarified the nature of this disease, and the accumulated materials in the lysosomes have been analyzed using biochemical techniques. In the present study, transmission electron microscopy was used to reveal the fine structure of these lysosomal deposits, and sugar residues in the lysosomal deposits in Fabry disease were examined by lectin histochemistry combined with enzyme digestion. This is the first report to describe the lysosomal sugar residues in Fabry disease analyzed using lectin histochemistry at the ultrastructural level. With these techniques, we were able to detect alpha-galactosyl, beta-galactosyl and glucosyl sugar residues in the lysosomal deposits. The experimental procedures used in this study have considerable potential for use in investigations of glycolipid and glycoprotein storage diseases without the need for complex methodology and expensive materials.

Ground squirrel model for cholelithiasis: role of epithelial glycoproteins

The cholesterol-fed Richardson's ground squirrel (Spermophilus richardsonii) has proven to be an effective animal model in which to study factors that influence cholesterol gallstone formation and associated alterations in the gallbladder epithelium. Ground squirrels of either sex, fed a 2% cholesterol-enriched diet, exhibit cholesterol monohydrate crystal precipitation within 24 hours and macroscopically visible cholesterol stones by 3 weeks. Data on bile chemistry, biliary cholesterol precipitation, and various mucosal alterations occurring prior to, during, and after stone formation were collected using sampling intervals from 6 hours to 20 weeks on the diet. The results indicate that mucin hypersecretion appears to be more closely related to the initiation of nucleation than does either bile calcium of pH. Mucus hypersecretion begins within 18 hours of diet initiation and continues throughout the 20 week experimental period. Apical excrescences became more common and were larger in size during the early stages of cholelithiasis. Administration of aspirin during the experimental period demonstrated an inhibition of mucin synthesis and release. Gallstones were not formed in these aspirin-treated animals. A lectin-binding panel for 10 epithelial glycoprotein-related sugars indicated the mucin secreted by the gallbladder epithelium of 7 day experimental animals differed from that of controls. The most obvious difference was the abolition of WGA binding in the experimental animals, suggesting an absence of sialic acid expression in the mucin during the lithogenic process. Ultrastructural histochemistry indicated that both sulphomucin and sialomucin were present in the secretory granules and within the surface mucus layer of both experimental and control animals. Experimental animals, however, exhibited a significant predominance for sulphomucin. This pattern varies from that typically seen in other regions of the gastrointestinal tract where sialomucins predominate during pathologic processes.

Cytological and lectin histochemical characterization of secretion production and secretion composition in the tubular glands of the canine anal sacs

The study reports on secretion production and composition in the tubular glands of the canine anal sacs. For this purpose, light and electron microscopical (TEM, SEM) as well as several histochemical methods for the demonstration of lysosomal acidity, lipofuscin, and complex carbohydrates were used. The glandular tubules exhibited a pseudostratified epithelium with secretory cells of a different shape as related to secretion production activity, and regionally varying amounts of basal cells. Flat, cuboidal or columnar cells with or without apocrine-like protrusions were assembled in one glandular endpiece, although grouping of these cell types often occurred. Active secretory cells were columnar with many cytoplasmic vesicles and a typically merocrine and/or micro-apocrine exocytosis of vesicle contents. Additionally, many lysosomes of different sizes could be found, whereby in aged cells giant secondary lysosomes (autophagolysosomes, about 7 microm in diameter) occupied the major cell part. These giant lysosomes were shed by an apocrine-like process forming a final bottleneck stage of the upper cell part, and consisted of ceroid-type lipofuscin. The general carbohydrate histochemical and the lectin histochemical methods revealed that the secretion produced was composed of strongly concentrated neutral glycoproteins with the following saccharide residues: alpha-D-mannose, beta-D-galactose, beta-N-acetyl-D-glucosamine, alpha-L-fucose and N-acetyl-neuraminic acid (sialic acid); the luminal secretion contained only beta-D-galactose and, especially, N-acetyl-neuraminic acid. This luminal secretion showed a spatially orientated maturation beginning in terminal tubular regions and finishing near the excretory duct, independent of the different secretory cell types. The results obtained demonstrated highly active secretion production, with a regional variation in the glandular tubule, and at least three different modes of secretion by the secretory cells, whereby the shedding of giant lipofuscin granules seems to be very specific. The high amounts of sialic acids in the glycoproteins found may influence the rheological properties of the secretion by their water-binding capacities.

Glycosylated nuclear lectin CBP70 also associated with endoplasmic reticulum and the Golgi apparatus: does the "classic pathway" of glycosylation also apply to nuclear glycoproteins?

The subcellular plurilocalization of some lectins (galectin-1, galectin-3, galectin-10, calreticulin, etc.) is an intriguing problem, implying different partners according to their localization, and involvement in a variety of cellular activities. For example, the well-known lectin, galectin-3, a lactose-binding protein, can act inside the nucleus in splicing events, and at the plasma membrane in adhesion, and it was demonstrated that galectin-3 interacts in the cytoplasm with Bcl-2, an antiapoptotic protein. Some years ago, our group isolated a nuclear lectin CBP70, capable of recognizing N-acetylglucosamine residues. This lectin, first isolated from the nucleus of HL60 cells, was also localized in the cytoplasm. It has been demonstrated that CBP70 is a glycosylated lectin, with different types of glycosylation, comparing cytoplasmic and nuclear forms. In this article, we have studied the localization of CBP70 in undifferentiated HL60 cells by electron microscopy, immunofluorescence analysis, and subcellular fractionation. The results obtained clearly demonstrated that CBP70 is a plurilocalized lectin that is found in the nucleus, at the endoplasmic reticulum, the Golgi apparatus, and mitochondria, but not at the plasma membrane. Because CBP70, a nuclear glycoprotein, was found to be associated also with the endoplasmic reticulum and the Golgi apparatus where the glycosylation take place, it raised the question: where does the glycosylation of nuclear proteins occur?

Serum amyloid P component (SAP)-like protein from botryllid ascidians provides a clue to amyloid function

The HA-1 lectin isolated from Botrylloides leachii has an amino acid composition similar to that of mammalian serum amyloid protein (SAP). SAP is a universal component of mammalian amyloid deposits. Like SAP, HA-1 has a disc ultrastructure, and antibody to HA-1 binds both (a) to amyloidlike fibers deposited between rejected Botrylloides colonies and (b) to cerebral amyloid deposits in Alzheimer's disease brains. Deposition of protochordate amyloid within rejection sites and surrounding fouling organisms implies that these fibers function as barriers to allogeneic and infectious challenge. Similarly, mammalian amyloid may also function to contain inflammatory lesions and to limit the spread of certain infections. Pathological amyloidotic conditions in humans, such as Alzheimer's disease, may result from unregulated expression of this primitive encapsulation response.

Biochemical and ultrastructural studies of the C-type lectin bovine conglutinin

The aim of this study was to correlate the supramolecular organization of conglutinin (BK) with its primary and tertiary structure and to gain more knowledge of functionally important regions of the molecule. BK analyzed by SDS-PAGE under standard reducing conditions (40 mM DTT) showed a major band at 43 kDa and weaker bands at 86 and 180 kDa. In contrast, reduction with 6-50 mM L-cysteine resulted in 37-kDa subunits indicating the presence of intrachain disulfide bonds within this subunit. Hydroxylamine treatment indicated presence of ester bonds in the 86- and 180-kDa subunits. Collagenase digestion and SDS-PAGE under reducing and nonreducing conditions resulted in bands of 20 and 15 kDa, respectively, indicating the presence of intrachain, rather than interchain, disulfide bonds in the carboxy terminus. Deglycosylation and glycan differentiation analysis of BK revealed the presence of O-linked glycans of GalNAc and alpha (2-3) linked sialic acid type, whereas no N-linked glycans were demonstrated. Binding experiments with GlcNAc-gold suggested that multivalency is required for carbohydrate binding to BK. Electron microscopy showed mostly tetramers, 96 nm in diameter, but also mono-, di-, and trimers were seen. The tetramers consisted of 40-nm strands, each with a peripheral globular head composed of subunits and connected to a common central lobe built from four ring-formed structures. The strands occasionally showed two bends, one close to the central lobe and another 25 nm from the lobe. These bends most likely correspond to the interrupted Gly-Xaa-Yaa repeats at residues 38 and 123.

Pyriform cell differentiation in Podarcis sicula is accompanied by the appearance of surface glycoproteins bearing alpha-galNAc terminated chains

The present histochemical and cytochemical study using a lectin panel (WGA, GSI-A4, GSI-B4, PSA UEA-I, PNA, LCA, Con-A, DBA, MPA, BPA) has demonstrated that, in Podarcis sicula, the differentiation of small follicle cells into pyriform cells by means of intermediate cells is accompanied by the appearance of glycoproteins bearing alpha-GalNAc terminated O-linked side chains on the cell surface. The distribution of DBA- and MPA-binding sites over the follicular epithelium changed during the different stages of oocyte growth. DBA- and MPA-binding sites first appeared at the beginning of folliculogenesis within the zona pellucida (ZP) and on the surface of small cells, i.e., the stem cells of pyriform cells. Afterward, labeling was evident on the cell surfaces of intermediate cells and, later on, also of pyriform cells. On the other hand, no labeling was detected on the small cells located under the basal lamina, which, reportedly, do not differentiate into pyriform cells (Filosa et al. J. Embryol. Exp. Morphol., 1979; 15:297-316). Once pyriform cells were differentiated, the distribution of DBA- and MPA-binding sites over the follicular epithelium remained unchanged until intermediate and pyriform cells underwent apoptosis (Motta et al. J. Exp. Zool., 1996; 276:233-241) and the follicular epithelium transformed into a monolayer composed of small follicle cells only (Filosa Mon. Zool. Ital., 1973; 7:151-165). During this stage of oocyte growth, DBA and MPA labeling gradually decreased to completely disappear in the follicular epithelium of vitellogenic follicles. It is noteworthy that the observed changes in the distribution of DBA- and MPA-binding sites represent the first evidence recognized by lectins of a gradual modification of surface glycoprotein distribution over the follicular epithelium in the ovarian follicles of nonmammalian vertebrates so far studied. Finally, the zona pellucida (ZP), characterized by the presence of GalNAc, GluNAc, Man, and Gal, was demonstrated to be first synthetized by the oocyte and later on by the follicle cells.

Streptomyces umbrella toxin particles block hyphal growth of competing species

Streptomyces are a genus of ubiquitous soil bacteria from which the majority of clinically utilized antibiotics derive1. The production of these antibacterial molecules reflects the relentless competition Streptomyces engage in with other bacteria, including other Streptomyces species1,2. Here we show that in addition to small-molecule antibiotics, Streptomyces produce and secrete antibacterial protein complexes that feature a large, degenerate repeat-containing polymorphic toxin protein. A cryo-electron microscopy structure of these particles reveals an extended stalk topped by a ringed crown comprising the toxin repeats scaffolding five lectin-tipped spokes, which led us to name them umbrella particles. Streptomyces coelicolor encodes three umbrella particles with distinct toxin and lectin composition. Notably, supernatant containing these toxins specifically and potently inhibits the growth of select Streptomyces species from among a diverse collection of bacteria screened. For one target, Streptomyces griseus, inhibition relies on a single toxin and that intoxication manifests as rapid cessation of vegetative hyphal growth. Our data show that Streptomyces umbrella particles mediate competition among vegetative mycelia of related species, a function distinct from small-molecule antibiotics, which are produced at the onset of reproductive growth and act broadly3,4. Sequence analyses suggest that this role of umbrella particles extends beyond Streptomyces, as we identified umbrella loci in nearly 1,000 species across Actinobacteria.

Natural and artificial carbohydrate-glued protein aggregates

Carbohydrate gluing (which may have a carbohydrate-lectin binding mechanism) was first recognized as a major contributor in the supramolecular assembly of annelid giant Hb from the marine-worm P. aibuhitensis. Although this assembly obviously also relies on protein-protein interactions, the authors tested the application of carbohydrate gluing in the assembly of a protein aggregate using a lectin and a carbohydrate-containing protein. The resultant aggregate was a mixture of the protein aggregate and the ingredient proteins. The significance of the method is that the assembly of the aggregate can be controlled by using a hapten sugar. This controllability, in conjunction with newly developing glyco-technology, has great potential for the construction of arbitrary protein molecules into a regular protein aggregate, thereby providing sophisticated functions.

Isolation and partial characterisation of four novel plasma lectins from the American lobster Homarus americanus

Although numerous haemolymph-derived crustacean lectins are described, few have been reported for the American lobster Homarus americanus. In the present study, affinity chromatography was used to isolate and partially describe the carbohydrate affinity of four new lectins from H. americanus plasma. HaMBP and HaDNABP were homodimers of approximately 30 kDa subunits which bound to mannan- and DNA-agarose columns, respectively. These proteins had partially overlapping elution profiles, and both shared and unique amino acid sequences and fragmentation patterns after trypsin digestion. A third homodimer of approximately 29 kDa subunits eluted with HaMBP and HaDNABP under certain conditions. HaNBP occurred as a monomer and dimer of approximately 40 kDa subunits and was recovered in relatively large quantities from mannan-agarose with N-acetylated sugars. Transmission electron microscopy revealed HaNBP to be a linear protein composed of multiple globular subunits.

Biophysical Characterization of the Non-Fusogenic Interaction Between Liposomes and the Shrimp Bifunctional Lipoprotein-β-Glucan Binding Protein HDL/BGBP

Shrimp High Density Lipoprotein-beta-Glucan Binding Protein (HDL/BGBP) has been studied by its role in nutrition and innate defense. Although the mechanisms of lipid loading are still unknown, HDL-BGBP binds and aggregates phospholipids vesicles in vitro. To gain insights into the HDL-BGBP mechanism of interaction with membranes, we have used fluorescence spectroscopy and electron microscopy. Data show that HDL-BGBP does not induce membrane fusion, leakage nor lipid exchange, although microstructural changes are clearly observed. This work supports a model where protein aggregation leads to liposome clustering. Such interaction may be a critical factor for the activation of the shrimp blood cell in vivo.

Serum carbohydrate-binding IgM are present in Vietnamese striped catfish (Pangasianodon hypophthalmus) but not in North African catfish (Clarias gariepinus)

Pangasianodon hypophthalmus serum was fractionated by affinity chromatography on 12 different Sepharose-carbohydrate columns and proteins eluted by the corresponding sugar. Binding to the affinity matrices is dependent on Ca(2+) ions. Upon gel filtration using Superose-12, essentially one fraction was obtained, eluting as a protein with a molecular mass of about 900 kDa. SDS-PAGE in reducing conditions revealed the presence of large (72 kDa) subunits (H-chains) and one up to three small (24, 26 and/or 28-29 kDa) subunits (L-chains). The isolated proteins were shown to be IgM since they bind monoclonal anti-P. hypophthalmus IgM antibodies. Rabbit polyclonal anti-galactose-binding IgM only cross-react with some sugar-binding IgM. The H-chains of the anti-carbohydrate IgM are glycosylated. Circular dichroism studies revealed that the IgMs have an "all-β" type of structure, and that Ca(2+) ions, though essential for carbohydrate-binding activity, are not required for the structural integrity of the molecules. In non-reducing SDS-PAGE, only monomers and halfmers were obtained, showing that there are no disulfide bonds linking the monomers, and that a disulfide bond connecting both H-chains within one monomer is only present in 45% of the molecules. Both the monomers and the halfmers display molecular mass heterogeneity which is indicative for redox forms at the level of the intradomain disulfide bonds. The native carbohydrate-binding IgMs agglutinate erythrocytes from different animals, as well as fish pathogenic bacteria. Similar proteins could not be isolated from another catfish, Clarias gariepinus.

Observation of unique cross-linked lattices between multiantennary carbohydrates and soybean lectin. Presence of pseudo-2-fold axes of symmetry in complex type carbohydrates

The tetrameric lectin from Glycine max (soybean) (SBA) has been shown to cross-link and precipitate with N-linked multiantennary complex type oligosaccharides containing nonreducing terminal Gal residues (Bhattacharyya, L., Haraldsson, M., & Brewer, C. F. (1988) Biochemistry 27, 1034-1041). In the present study, negative stain electron micrographs of the precipitates of SBA with a series of naturally occurring and synthetic multiantennary carbohydrates with terminal Gal or GalNAc residues show the presence of highly ordered cross-linked lattices for many of the complexes. The precipitates of SBA with a "bisected" and "nonbisected" N-linked biantennary complex type oligosaccharide containing Gal residues at the nonreducing termini show similar two-dimensional patterns. However, the pattern observed for the precipitates of a tetraantennary complex type oligosaccharide with SBA is distinct from those of the two biantennary carbohydrates. Furthermore, the precipitates formed between the lectin and a synthetic O-linked biantennary ("cluster") glycoside with terminal GalNAc residues show a pattern that is different from those above. Four biantennary pentasaccharide analogs of the blood group I antigen containing beta-LacNAc moieties at the 2.3-, 2.4-, 2.6-, and 3.6-positions of the core Gal also showed ordered patterns in their precipitates with SBA. X-ray crystallographic data and mixed quantitative precipitation profiles of binary mixtures of the four analogs demonstrate that each analog possesses a unique cross-linked lattice with the protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of the endogenous lectin CSL in adhesion of Chinese hamster ovary cells

Immunochemical localization of an endogenous mannose-binding protein, the cerebellar soluble lectin (CSL; Zanetta et al., J. Neurochem. 49, 1250-1257 (1987)), in Chinese hamster ovary cells indicated its high concentration in areas of contact between cells. This suggested its role in cell adhesion. The pattern of staining differed significantly in the cells cultured in suspension from that grown as monolayer. In cells maintained for a short time as suspension, the extracellular CSL immunoreactivity was found mainly in close apposition to the plasma membrane including contact areas. In cells cultured as monolayer, extracellularly, the lectin was found both at the cell surface and in a 75-nm thick layer between two cells, apparently adhering to the cell surface through bridges. Endogenous glycoprotein ligands of CSL were present in the cultures of CHO cells, both as membrane-bound glycoproteins and as glycoprotein ligands soluble in the presence of mannose in the absence of detergent. The lectin CSL induced adhesion between these cells as evident by low concentration of anti-CSL Fab fragments inhibiting such adhesion. These data suggested that adhesion between CHO cells occurs, in part, through a glycobiological recognition system involving CSL. This mechanism should be taken into account for the interpretation of experiments of transfection in CHO cells of the genes of glycoproteins involved in cell adhesion.

An improved postembedding technique for ultrastructural studies of lectin binding sites in bone marrow: a critical evaluation

Little is known about the ultrastructural localization of lectin binding sites in human bone marrow tissue. This is probably due to the lack of suitable methods yielding both satisfactory tissue preservation and optimal labelling results. For this reason, we developed a modified postembedding technique for electron-microscopic studies of the glycosylation pattern of haematopoietic cells. Fixation with a 2.5% glutardialdehyde solution was shown to be an important prerequisite and could be even improved by postfixation with tannic acid and uranyl acetate. In particular, embedding with the acrylic resin UnicrylR (Bioacryl) resulted in an optimal ultrastructural preservation of bone marrow tissue. Employment of this hydrophilic resin in combination with a two-step labelling method which included digoxigenin-conjugated Concanavalin A (Con A) followed by ultrasmall anti-digoxigenin-gold and silver amplification, delivered a highly specific staining pattern. Our results with this lectin in different bone marrow cells revealed nuclear and cytoplasmic membranes, rough endoplasmic reticulum as well as granules to display reactivity of varying intensity. These findings underline the validity of our method, for they confirm and extend formerly reported histochemical and biochemical evaluations on the cellular binding sites of Con A.

Linking microfilaments to intracellular membranes: the actin-binding and vesicle-associated protein comitin exhibits a mannose-specific lectin activity

Comitin is a 24 kDa actin-binding protein from Dictyostelium discoideum that is located primarily on Golgi and vesicle membranes. We have probed the molecular basis of comitin's interaction with both actin and membranes using a series of truncation mutants obtained by expressing the appropriate cDNA in Escherichia coli. Comitin dimerizes in solution; its principle actin-binding activity is located between residues 90 and 135. The N-terminal 135 'core' residues of comitin contain a 3-fold sequence repeat that is homologous to several monocotyledon lectins and which retains key residues that determine these lectins' three-dimensional structure and mannose binding. These repeats of comitin appear to mediate its interaction with mannose residues in glycoproteins or glycolipids on the cytoplasmic surface of membrane vesicles from D.discoideum, and comitin can be released from membranes with mannose. Our data indicate that comitin binds to vesicle membranes via mannose residues and, by way of its interaction with actin, links these membranes to the cytoskeleton.

Production and characterization of monoclonal antibodies against bacterial lectin of Eikenella corrodens

A lectin-like substance (EcLS) was purified from the Eikenella corrodens 1073 cell and monoclonal antibodies were produced against it to confirm the role of EcLS in adhesive properties of E. corrodens such as hemagglutination and coaggregation with oral bacteria. Four hybridoma clones were selected. Two of the antibodies were of the IgG1 isotype and the others were of the IgG2b isotype. These monoclonal antibodies inhibited both the hemagglutination of E. corrodens and the coaggregation with Actinomyces viscosus or Streptococcus sanguis. The reactivity of the monoclonal antibody to E. corrodens 1073 was significantly higher than that to E. corrodens 1080 of which adhesive activity was weaker than that of E. corrodens 1073. These findings suggest the difference in adhesive properties is due to the difference in the amount of EcLS expressed on the cell surface. The immunoelectron microscopic study revealed that EcLS of E. corrodens 1073 was localized in the outer space of outer membrane, not in cell surface appendages such as fimbriae where bacteria possessed adhesin. These results suggest that coaggregation of E. corrodens with A. viscosus or S. sanguis was mediated by EcLS.