The interactions of lectins with animal cell surfaces

Targeting osteoarthritis-associated galectins and an induced effector class by a ditopic bifunctional reagent: Impact of its glycan part on binding measured in the tissue context

Pairing glycans with tissue lectins controls multiple effector pathways in (patho)physiology. A clinically relevant example is the prodegradative activity of galectins-1 and -3 (Gal-1 and -3) in the progression of osteoarthritis (OA) via matrix metalloproteinases (MMPs), especially MMP-13. The design of heterobifunctional inhibitors that can block galectin binding and MMPs both directly and by preventing their galectin-dependent induction selectively offers a perspective to dissect the roles of lectins and proteolytic enzymes. We describe the synthesis of such a reagent with a bivalent galectin ligand connected to an MMP inhibitor and of two tetravalent glycoclusters with a subtle change in headgroup presentation for further elucidation of influence on ligand binding. Testing was performed on clinical material with mixtures of galectins as occurring in vivo, using sections of fixed tissue. Two-colour fluorescence microscopy monitored binding to the cellular glycome after optimization of experimental parameters. In the presence of the inhibitor, galectin binding to OA specimens was significantly reduced. These results open the perspective to examine the inhibitory capacity of custom-made ditopic compounds on binding of lectins in mixtures using sections of clinical material with known impact of galectins and MMPs on disease progression.

Fifty Years of the Fluid–Mosaic Model of Biomembrane Structure and Organization and Its Importance in Biomedicine with Particular Emphasis on Membrane Lipid Replacement

The Fluid–Mosaic Model has been the accepted general or basic model for biomembrane structure and organization for the last 50 years. In order to establish a basic model for biomembranes, some general principles had to be established, such as thermodynamic assumptions, various molecular interactions, component dynamics, macromolecular organization and other features. Previous researchers placed most membrane proteins on the exterior and interior surfaces of lipid bilayers to form trimolecular structures or as lipoprotein units arranged as modular sheets. Such membrane models were structurally and thermodynamically unsound and did not allow independent lipid and protein lateral movements. The Fluid–Mosaic Membrane Model was the only model that accounted for these and other characteristics, such as membrane asymmetry, variable lateral movements of membrane components, cis- and transmembrane linkages and dynamic associations of membrane components into multimolecular complexes. The original version of the Fluid–Mosaic Membrane Model was never proposed as the ultimate molecular description of all biomembranes, but it did provide a basic framework for nanometer-scale biomembrane organization and dynamics. Because this model was based on available 1960s-era data, it could not explain all of the properties of various biomembranes discovered in subsequent years. However, the fundamental organizational and dynamic aspects of this model remain relevant to this day. After the first generation of this model was published, additional data on various structures associated with membranes were included, resulting in the addition of membrane-associated cytoskeletal, extracellular matrix and other structures, specialized lipid–lipid and lipid–protein domains, and other configurations that can affect membrane dynamics. The presence of such specialized membrane domains has significantly reduced the extent of the fluid lipid membrane matrix as first proposed, and biomembranes are now considered to be less fluid and more mosaic with some fluid areas, rather than a fluid matrix with predominantly mobile components. However, the fluid–lipid matrix regions remain very important in biomembranes, especially those involved in the binding and release of membrane lipid vesicles and the uptake of various nutrients. Membrane phospholipids can associate spontaneously to form lipid structures and vesicles that can fuse with various cellular membranes to transport lipids and other nutrients into cells and organelles and expel damaged lipids and toxic hydrophobic molecules from cells and tissues. This process and the clinical use of membrane phospholipid supplements has important implications for chronic illnesses and the support of healthy mitochondria, plasma membranes and other cellular membrane structures.

Comparative Cellular Localization of Sugar Residues in Bull (Bos taurus) and Donkey (Equus asinus) Testes Using Lectin Histochemistry

Lectins are glycoproteins of a non-immune origin often used as histochemical reagents to study the distribution of glycoconjugates in different types of tissues. In this study, we performed a comparative cellular localization of sugar residues in bull and donkey testes using immunofluorescent lectin histochemistry. We inspected the cellular localization of the glycoconjugates within the testes using 11 biotin-labeled lectins (LCA, ConA, PNA, WGA, DBA, SBA, ECA, BPL, PTL-II, UEA-1, and PHA-E4) classified under six groups. Although the basic testicular structure in both species was similar, the cellular components showed different lectin localization patterns. The statistical analysis revealed no significant association between the intensity of labeling and different variables, including group and type of lectin and type of cell examined, at p < 0.05. However, a stronger response tended to occur in the donkey than in the bull testes (odds ratio: 1.3). These findings may be associated with the different cellular compositions of the glycoproteins and modification changes during spermatogenesis. Moreover, glycoconjugate profiling through lectin histochemistry can characterize some cell-type selective markers that will be helpful in studying bull and donkey spermatogenesis.

Imitating evolution's tinkering by protein engineering reveals extension of human galectin-7 activity

Wild-type lectins have distinct types of modular design. As a step to explain the physiological importance of their special status, hypothesis-driven protein engineering is used to generate variants. Concerning adhesion/growth-regulatory galectins, non-covalently associated homodimers are commonly encountered in vertebrates. The homodimeric galectin-7 (Gal-7) is a multifunctional context-dependent modulator. Since the possibility of conversion from the homodimer to hybrids with other galectin domains, i.e. from Gal-1 and Gal-3, has recently been discovered, we designed Gal-7-based constructs, i.e. stable (covalently linked) homo- and heterodimers. They were produced and purified by affinity chromatography, and the sugar-binding activity of each lectin unit proven by calorimetry. Inspection of profiles of binding of labeled galectins to an array-like platform with various cell types, i.e. sections of murine epididymis and jejunum, and impact on neuroblastoma cell proliferation revealed no major difference between natural and artificial (stable) homodimers. When analyzing heterodimers, acquisition of altered properties was seen. Remarkably, binding properties and activity as effector can depend on the order of arrangement of lectin domains (from N- to C-termini) and on the linker length. After dissociation of the homodimer, the Gal-7 domain can build new functionally active hybrids with other partners. This study provides a clear direction for research on defining the full range of Gal-7 functionality and offers the perspective of testing applications for engineered heterodimers.

Characterizing ligand-induced conformational changes in clinically relevant galectin-1 by HN/H2O (D2O) exchange

Glycans of cellular glycoconjugates serve as biochemical signals for a multitude of (patho)physiological processes via binding to their receptors (e.g. lectins). In the case of human adhesion/growth-regulatory galectin-1 (Gal-1), small angle neutron scattering and fluorescence correlation spectroscopy have revealed a significant decrease of its gyration radius and increase of its diffusion coefficient upon binding lactose, posing the pertinent question on the nature and region(s) involved in the underlying structural alterations. Requiring neither a neutron source nor labeling, diffusion measurements by ¹H NMR spectroscopy are shown here to be sufficiently sensitive to detect this ligand-induced change. In order to figure out which region(s) of Gal-1 is (are) affected at the level of peptides, we first explored the use of H/D exchange mass spectrometry (HDX MS). Hereby, we found a reduction in proton exchange kinetics beyond the lactose-binding site. The measurement of fast H^N/H₂O exchange by phase-modulated NMR clean chemical exchange (CLEANEX) NMR on ¹⁵N-labeled Gal-1 then increased the spatial resolution to the level of individual amino acids. The mapped regions with increased protection from H^N/H₂O (D₂O) exchange that include the reduction of solvent exposure around the interface can underlie the protein's compaction. These structural changes have potential to modulate this galectin's role in lattice formation on the cell surface and its interaction(s) with protein(s) at the F-face.

Concanavalin a and Wheat Germ Agglutinin Receptors in the Ascitic Fluid of Rat Hepatomas

The presence of glycopeptide lectin receptors in the ascitic fluid of rats bearing Novikoff or AS-30D hepatoma was investigated. Macrosialoglycopeptides, resistant to pronase digestion, were partially purified from the ascitic fluid of hepatoma-bearing rats by gel filtration on Sephadex G-50. A macrosialoglycopeptide fraction, isolated from the ascitic fluid of rats bearing the Novikoff hepatoma, possessed potent concanavalin A (Con A) receptor activity. This fraction possessed higher Con A receptor activity than did the comparable macrosialoglycopeptide fraction from the ascitic fluid of rats bearing the AS-30D hepatoma; this observation is in agreement with the Con A-induced agglutination properties of these 2 hepatoma cell lines and with the Con A receptor activities of the glycopeptides released from the surface of the hepatoma cells by papain digestion. Rat blood serum contained a comparable macrosialoglycopeptide fraction, which possessed weak Con A receptor activity. The macrosialoglycopeptide fractions from the ascitic fluid of hepatoma-bearing rats possessed wheat germ agglutinin receptor activity. However, this activity was also present in normal rat serum. These results suggest that glycopeptides present on the surface of Novikoff hepatoma cells are shed into the ascitic fluid and may be distinguished from components in normal serum by their Con A receptor activity.

Revealing biomedically relevant cell and lectin type-dependent structure–activity profiles for glycoclusters by using tissue sections as an assay platform

The increasing realization of the involvement of lectin-glycan recognition in (patho)physiological processes inspires envisioning therapeutic intervention by high-avidity/specificity blocking reagents. Synthetic glycoclusters are proving to have potential for becoming such inhibitors but the commonly used assays have their drawbacks to predict in vivo efficacy. They do not represent the natural complexity of (i) cell types and (ii) spatial and structural complexity of glycoconjugate representation. Moreover, testing lectins in mixtures, as present in situ, remains a major challenge, giving direction to this work. Using a toolbox with four lectins and six bi- to tetravalent glycoclusters bearing the cognate sugar in a model study, we here document the efficient and versatile application of tissue sections (from murine jejunum as the model) as a platform for routine and systematic glycocluster testing without commonly encountered limitations. The nature of glycocluster structure, especially core and valency, and of protein features, i.e. architecture, fine-specificity and valency, are shown to have an influence, as cell types can differ in response profiles. Proceeding from light microscopy to monitoring by fluorescence microscopy enables grading of glycocluster activity on individual lectins tested in mixtures. This work provides a robust tool for testing glycoclusters prior to considering in vivo experiments.

Introducing tissue sections for testing glycocluster activity as inhibitors of lectin binding close to in vivo conditions.

Thermodynamics of chemical Marangoni-driven engines

The goal of this paper is to perform a general thermodynamic study of Marangoni-driven engines in which chemical energy is directly transformed into mechanical motion. Given that this topic has not been discussed before, we will explore here the most basic and fundamental aspects of the phenomena at work, which leads to a number of interesting observations typical of controversies in classical thermodynamics. Starting with a discussion of a few key motivating examples of chemical Marangoni-driven phenomena - tears of wine, an oscillating pendant droplet, "beating" oil lens, and traveling waves in a circular container - and contrasting homogeneous versus inhomogeneous thermodynamic systems we naturally arrive at alternative ways of storing and generating energy with the help of inhomogeneities in the bulk and surface properties of the working media. Of particular interest here are systems with interfaces - hence, in this context we discuss the nature and efficiency of the corresponding thermodynamic cycles leading to work done as a result of a non-uniform distribution of surface tension, which is in turn induced by a non-uniform surface active substance (surfactant) distribution, for both soluble and insoluble surfactants. Based on the relevant physical parameters of the working medium we can also evaluate the isothermality, i.e. temperature variations, dissipative losses, energy output and efficiency, entropy generation, and the period of such cycles in real processes. The role of singularity formation at the interface for the existence of such thermodynamic cycles is unraveled as well. Finally the discussion is concluded with a few ideas for potential applications of Marangoni-driven engines.

Antiviral lectins: Selective inhibitors of viral entry

Many natural lectins have been reported to have antiviral activity. As some of these have been put forward as potential development candidates for preventing or treating viral infections, we have set out in this review to survey the literature on antiviral lectins. The review groups lectins by structural class and class of source organism we also detail their carbohydrate specificity and their reported antiviral activities. The review concludes with a brief discussion of several of the pertinent hurdles that heterologous proteins must clear to be useful clinical candidates and cites examples where such studies have been reported for antiviral lectins. Though the clearest path currently being followed is the use of antiviral lectins as anti-HIV microbicides via topical mucosal administration, some investigators have also found systemic efficacy against acute infections following subcutaneous administration.

WGA-Alexa Conjugates for Axonal Tracing

Anatomical labeling approaches are essential for understanding brain organization. Among these approaches are various methods of performing tract tracing. However, a major hurdle to overcome when marking neurons in vivo is visibility. Poor visibility makes it challenging to image a desired neuronal pathway so that it can be easily differentiated from a closely neighboring pathway. As a result, it becomes impossible to analyze individual projections or their connections. The tracer that is chosen for a given purpose has a major influence on the quality of the tracing. Here, we describe the wheat germ agglutinin (WGA) tracer conjugated to Alexa fluorophores for reliable high-resolution tracing of central nervous system projections. Using the mouse cerebellum as a model system, we implement WGA-Alexa tracing for marking and mapping neural circuits that control motor function. We also show its utility for marking localized regions of the cerebellum after performing single-unit extracellular recordings in vivo. © 2017 by John Wiley & Sons, Inc.

Sweet complementarity: the functional pairing of glycans with lectins

Carbohydrates establish the third alphabet of life. As part of cellular glycoconjugates, the glycans generate a multitude of signals in a minimum of space. The presence of distinct glycotopes and the glycome diversity are mapped by sugar receptors (antibodies and lectins). Endogenous (tissue) lectins can read the sugar-encoded information and translate it into functional aspects of cell sociology. Illustrated by instructive examples, each glycan has its own ligand properties. Lectins with different folds can converge to target the same epitope, while intrafamily diversification enables functional cooperation and antagonism. The emerging evidence for the concept of a network calls for a detailed fingerprinting. Due to the high degree of plasticity and dynamics of the display of genes for lectins the validity of extrapolations between different organisms of the phylogenetic tree yet is inevitably limited.

Purification, characterization, and mitogenic potential of a mucin-specific mycelial lectin from Aspergillus sparsus

Lectins are carbohydrate binding proteins or glycoproteins that bind reversibly to specific carbohydrates present on the apposing cells, which is responsible for their ability to agglutinate red blood cells, lymphocytes, fibroblasts, etc. Due to their carbohydrate specificity, lectins have been used for purification and characterization of glycoproteins like antibodies, cytokines, tumor-associated glycoproteins, hormones, inhibitors, growth factors, various enzymes, membrane proteins (receptors), or even toxins and viruses. In the present study, a mycelial lectin from Aspergillus sparsus was purified, characterized, and evaluated for its mitogenic potential. Lectin could be effectively purified 17.8-fold in a single-step using affinity chromatography on mucin-sepharose column. Lectin migrated as a single band in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) with an apparent molecular mass of 100.2 kDa. Lectin showed pH optima of 6.5-8.0, and optimum temperature was determined to be 20-30 °C. Lectin was stable within a pH range of 5.5-10.0 and showed fairly good thermostability. Lectin activity was unaffected in the presence of EDTA, while activity reduced upon interaction with denaturants. MTT assay revealed strong mitogenic potential of A. sparsus lectin at a concentration up to 100 μg/ml.

Complex N-glycans: the story of the "yellow brick road"

The synthesis of complex asparagine-linked glycans (N-glycans) involves a multi-step process that starts with a five mannose N-glycan structure: [Manα1-6(Manα1-3)Manα1-6][Manα1-3]-R where R = Manβ1-4GlcNAcβ1-4GlcNAcβ1-Asn-protein. N-acetylglucosaminyltransferase I (GlcNAc-TI) first catalyzes addition of GlcNAc in β1-2 linkage to the Manα1-3-R terminus of the five-mannose structure. Mannosidase II then removes two Man residues exposing the Manα1-6 terminus that serves as a substrate for GlcNAc-T II and addition of a second GlcNAcβ1-2 residue. The resulting structure is the complex N-glycan: GlcNAcβ1-2Manα1-6(GlcNAcβ1-2Manα1-3)-R. This structure is the precursor to a large assortment of branched complex N-glycans involving four more N-acetylglucosaminyltransferases. This short review describes the experiments (done in the early 1970s) that led to the discovery of GlcNAc-TI and II.

Biological activities of ACL-I and physicochemical properties of ACL-II, lectins isolated from the marine sponge Axinella corrugata

Lectin II from the marine sponge Axinella corrugata (ACL-II) was purified by affinity chromatography on rabbit erythrocytic stroma incorporated into a polyacrylamide gel, followed by gel filtration on Ultrogel AcA 44 column. Purified ACL-II is a lectin with an Mr of 80 kDa and 78 kDa, estimated by SDS-PAGE and by FPLC on Superose 12 HR column, respectively. ACL-II mainly agglutinates native rabbit erythrocytes and this hemagglutinating activity is independent of Ca(2+), Mg(2+) and Mn(2+), but is inhibited by d-galactose, chitin and N-acetyl derivatives, with the exception of GalNAc. ACL-II is stable for up to 65 °C for 30 min, with a better stability at a pH range of 2 to 6. In contrast, ACL-I displays a strong mitogenic and cytotoxic effect.

Toxin-based therapeutic approaches

Protein toxins confer a defense against predation/grazing or a superior pathogenic competence upon the producing organism. Such toxins have been perfected through evolution in poisonous animals/plants and pathogenic bacteria. Over the past five decades, a lot of effort has been invested in studying their mechanism of action, the way they contribute to pathogenicity and in the development of antidotes that neutralize their action. In parallel, many research groups turned to explore the pharmaceutical potential of such toxins when they are used to efficiently impair essential cellular processes and/or damage the integrity of their target cells. The following review summarizes major advances in the field of toxin based therapeutics and offers a comprehensive description of the mode of action of each applied toxin.

Improvement of in vitro oocyte maturation with lectin supplementation and expression analysis of Cx43, GDF-9, FGF-4 and Fibronectin mRNA transcripts in Buffalo (Bubalus bubalis)

PURPOSE

To optimize In vitro maturation (IVM) of quality oocytes for embryo production through IVF and SCNT.

METHODS

Buffalo oocytes were in vitro matured in the presence of the pokeweed lectin (Phytolacca americana), a potent lymphocyte mitogen. Lectin was supplemented in TCM + 10% FBS at the doses of 0, 1, 5, 10, 15, 20 and 40 microg/ml and cumulus expansion and gene expression patterns were characterized.

RESULTS

The degree of cumulus expansion in different lectin treatment levels improved from 1.1 at 1 Ag/ml level to 3.60 at 10 microg/ml level and then decreased in higher concentration 20 microg/ml (1.66) and 40 microg/ml (0.64). IVF embryos showed highest cleavage rate (88.8%) in 10 microg/ml lectin treatment. Expression of all mRNA transcript studied (Cx43, GDF 9, FGF-4 and Fibronectin) was positively correlated with cumulus expansion and polar body extrusion.

CONCLUSIONS

Mitogenic lectin supplemented maturation media improves oocyte quality for in vitro embryo production.

Lectins: past, present and future

Lectins, a class of sugar-binding and cell-agglutinating proteins, are ubiquitous in Nature, being found in all kinds of organisms, from viruses to humans. This review describes how plant lectins were developed as widely used reagents for the study of glycoconjugates in solution and on cells, and for cell characterization and separation. A summary is then given of the discoveries that demonstrated the role of lectins as cell recognition molecules of micro-organisms and of animal cells. The specialized functions of these lectins are discussed, as well as the potential medical applications of the knowledge gained. The review ends with speculations about future developments in lectin research and applications.

Novel lectins from rhizomes of two Acorus species with mitogenic activity and inhibitory potential towards murine cancer cell lines

Two novel lectins were purified from rhizomes of two sweet flag species, namely Acorus calamus (Linn.) and Acorus gramineus (Solandin Ait.) by affinity chromatography on mannose linked epoxy-activated Sepharose 6B. The apparent molecular mass of the lectins, as determined by gel filtration chromatography, was 56 kDa for ACL and 55 kDa for AGL. In SDS-PAGE, pH 8.3, both lectins migrated with a subunit molecular mass of 13.6 kDa and 13.5 kDa, respectively, under reducing and non-reducing conditions thus indicating the absence of disulphide linkages. Acorus lectins readily agglutinated rabbit, rat and guinea pig erythrocytes. Both ACL and AGL also reacted with RBCs from sheep, goat and human ABO blood groups after neuraminidase treatment. ACL and AGL were inhibited by mannose/glucose and their derivatives. The most effective inhibitor was methyl-alpha-D-mannopyranoside. Acorus lectins were stable up to 55 degrees C, did not require metal ions for their activity and were also affected by high concentrations of denaturants like urea, thiourea and guanidine-HCl. These lectins showed potent mitogenic activity towards mouse splenocytes and human lymphocytes. Both ACL and AGL also significantly inhibited the growth of J774, a murine macrophage cancer cell-line and to lesser extent WEHI-279, a B-cell lymphoma.

Lectins: from basic science to clinical application in cancer prevention

Many physiological functions are attributable to lectin-carbohydrate interactions. Lectins are currently being studied for their ability to destroy tumour growth by binding to specific carbohydrate motifs on cancer cells. Cell-surface molecules, including growth factor receptors are often glycosylated, and lectins may act by binding to these. Certain lectins effect the proliferation of intestinal epithelial cells. This effect is cell-type and lectin specific and occurs in the intestine of intact animals, in human colonic explants and colorectal cancer cell lines. Lectins present in mammalian tissue are involved in cell-matrix adhesion, differentiation, lymphocyte circulation and immunomodulation. Mammalian lectins contribute to detection, diagnosis and prognosis of tumour cells, and can be targeted for therapy. New lectins of plant and mammalian origin that have one or more of these functions are currently being developed as tools that could be used to target tumour cells.

Leptomonas wallacei shows distinct morphology and surface carbohydrates composition along the intestinal tract of its host Oncopeltus fasciatus (Hemiptera: Lygaeidae) and in axenic culture

Leptomonas wallacei is a monoxenic trypanosomatid that colonizes the digestive tract of the phytophagous hemipteran Oncopeltus fasciatus. This infection was specific and took place exclusively in midgut intestinal ventricles V3 and V4, and in the hindgut. Abundances of parasites in the hindgut were 54% less than those in the hindgut. Parasites in the hindgut were more slender and had a longer flagellum than those from the hindgut, which were rounded, with a shorter flagellum. Moreover, hindgut forms expressed sugar residues on the cell surface, recognized by the lectins from Griffonia simplicifolia-I (alpha-galactose, alpha-N-acetyl-galactosamine) and Helix pomatia (N-acetyl-galactosamine); those sugar residues were not present in protozoa from the midgut. In culture, parasites were morphologically similar to midgut forms, but differed from them because they did not express sugar residues that bind to lectin (beta-galactose(1-3) N-acetyl-galactosamine) from Arachis hypogaea.

Molecular anatomy of the cerebral microvessels in the isolated guinea-pig brain

Isolated organ preparations represent valuable models for biomedical research, provided that the functional and morphological integrity of vascular and parenchymal compartments is preserved. In this investigation, we have studied the molecular organization of the cerebral microvessels in the isolated guinea-pig brain maintained in vitro by arterial perfusion, a preparation previously proposed as a model of blood-brain barrier (BBB). Using lectin cytochemistry and immunohistochemistry, we examined the microvasculature of the cerebral cortex after 5 h in vitro to assess: (a) the structure of the endothelial glycocalyx at microscopical and ultrastructural level; (b) the distribution of the junctional molecules occludin, ZO-1, PECAM-1 and vinculin; (c) the distribution of basal lamina molecules, such as collagen type IV, laminin and heparan sulfate proteoglycan. All these components of microvessel wall have been previously shown to be vulnerable to ischemic conditions and their organization could be altered in consequence of the transient hypoxia associated with the brain isolation procedure. Our observations demonstrate that the distribution pattern of the molecules considered (i) is comparable to that shown in the cerebral microvasculature of other mammals and (ii) is similar in brains maintained in vitro and in control brains perfused in situ with fixative. The complex of our observation indicates that the molecular organization of the cerebral microvessels is preserved in isolated guinea-pig brain, thus indicating that these preparations can be used to study the cerebrovascular structure and blood-brain barrier function in a variety of experimental conditions.

Expression of binding properties of Gal/GalNAc reactive lectins by mammalian glycotopes (an updated report)

Expression of the binding properties of Gal/GalNAc specific lectins, based on the affinity of decreasing order of mammalian glycotopes (determinants) rather than monosaccharide inhibition pattern, is probably one of the best ways to express carbohydrate specifity and should facilitate the selection of lectins as structural probes for studying mammalian glycobiology. Eleven mammalian structural units have been selected to express the binding domain of applied lectins. They are: 1. F, GalNAcalpha1 --> 3GalNAc; 2. A, GalNAcalpha1 --> 3Gal; 3. T, Galbeta1 --> 3GalNAc; 4. I, Galbeta 1 --> 3GlcNAc; 5. II, Galbeta1 --> 4GlcNAc; 6. B, Galalpha1 --> 3Gal; 7. E, Galalpha1--> 4Gal; 8. L, Galbeta1 --> 4Glc; 9. P, GalNAcbeta1 --> 3Gal; 10. S, GalNAcbeta1 --> 4Gal and 11. Tn, GalNAcalpha1 --> 4Ser (Thr) of the peptide chain. Thus, the carbohydrate specificity of Gal/GalNAc reactive lectins can be divided into classes according to their highest affinity for the above disaccharides and/or Tn residue. Examples of the binding properties of these lectins can be demonstrated by Ricimus communis agglutinin (RCA1), grouped as II specific lectin and its binding property is II > I > B > T; Ahrus precatorius agglutinin (APA), classified as T and its carbohydrate specificity is T > I/II > E > B > Tn; Artocarpus integrifolia (jacalin, AIL), as T/Tn specific and its binding reactivity is T > Tn >> I (II) and Geodia cydonium (GCL), as F/A specific, and with affinity for F > Ah [GalNAcalpha1-->43(L(Fuc)alpha1-->2)Gal] >> I > L. Due to the multiple reactivity of lectins toward mammalian glycotopes, the possible existence of different combining sites or subsites in the same molecule has to be examined, and the differential binding properties of these combining sites (if any) have to be characterized. To establish the relationship among the amino acid sequences of the combining sites of plant lectins and mammalian glycotopes should be an important direction to be addressed in lectinology.

Life Cycle of Decidual Cells

The decisive events in the development of decidual cells (DC) are presented through examples of human and rodent decidua. Human decidua is formed by large decidual cells (LDC), endometrial granulated cells (eGC), and small decidual cells. The LDC form the main type of decidual membranes, which determine the morphological characteristics of the decidua as a tissue. Immediate precursor cells of LDC are located below the basement membrane of the uterine epithelium before and during implantation. At the next stage of differentiation, LDC acquire a spindle-like shape. Rodent LDC form an epithelium-like structure with gland properties at the terminal stage of differentiation. The single-cell structure of human decidua is a derivative of the epithelial organization of rodent decidua. Spindle-like rat LDC are characterized by a high level of protein, RNA, and DNA synthesis and by intensive proliferation. At the beginning of pregnancy, a cell proliferation predominates over cell loss. By Days 12-13 of rat pregnancy LDC loss reaches 80% per day. Terminally differentiated LDC (tLDC) disappear from decidua due to apoptosis. Apoptosis of tLDC and the exhaustion of their precursors account for the disappearance of LDC in the middle of rat pregnancy. Human term decidua is composed of living cells. Human LDC (hLDC) comprise the largest part of human decidual cells (hLDC). hLDC account for 60-90% of hDC but their relative amount can decrease to 35% in the case of significant cell loss under unfavorable conditions. A decrease of LDC is not accompanied by DC proliferation. The lack of ability of decidua to compensate for DC loss suggests DC is a growing type of cell population without cambial cells. LDC function largely by blebbing and budding. Human and rat endometrial granulated cells (eGC) are characterized by a low level of natural killer (NK) activity and a high level of natural suppressor (NS) activity. The combination of NK and NS properties is characteristic of the eGC immunoregulatory function. Other functions of decidua include control of inflammation and trophoblast growth and expansion in the uterus. The life span of decidual cells is limited by pregnancy.

Glycocalyx of lung epithelial cells

Due to their diversity and external location on cell membranes, glycans, as glycocalyx components, are key elements in eukaryotic cell, tissue, and organ homeostasis. Although information on the lung glycocalyx is scarce, this article aims to review, discuss, and summarize what is known about bronchoalveolar glycocalyx composition, mainly the sialic acids. It was deemed relevant, however, to make a brief introductory overview of the cell glycocalyx and its particular development in epithelial cells. After that, follows a summary of the evolution of the knowledge regarding the bronchoalveolar glycocalyx composition throughout the years, particularly its morphological features. Since sialic acids are located terminally on the bronchoalveolar lining cells' glycocalyx and play crucial roles, we focused mainly on the existing lung histochemical and biochemical data of these sugar residues, as well as their evolution throughout lung development. The functions of the lung glycocalyx sialic acids are discussed and interpretations of their roles analyzed, including those related to the negative overall superficial shield provided by these molecules. The increasing presence of these sugar residues throughout postnatal lung development should be regarded as pivotal in the development and maintenance of a dynamic bronchoalveolar architecture, supporting the normal histophysiology of the respiratory system. The case for a profound knowledge of lung glycocalyx--given its potential to provide answers to serious clinical problems--is made with particular reference to cystic fibrosis. Finally, concluding remarks and perspectives for future research in this field are put forth.

SEM visualization of glycosylated surface molecules using lectin-coated microspheres

There are several techniques currently used to localize glycosylated surface molecules by scanning electron microscopy (Grinnell, 1980; Molday, 1976; Linthicum and Sell, 1975; Nicolson, 1974; Lo Buglio, et al, 1972). A simple and rapid method, using a modification of Grinnell's technique is reported here. Essentially, microspheres coated with Concavalin A are used to bind to glycosylated regions of the palatal shelf epithelium and are visualized in the scanning electron microscope (SEM).

Specificity of the binding site of the sialic acid-binding lectin from ovine placenta, deduced from interactions with synthetic analogues

The specificity of the sialic acid-binding lectin from ovine placenta was examined in detail by haemagglutination inhibition assays applying a panel of 32 synthetic sialic acid analogues. The carboxylic acid group is a prerequisite for the interaction with the lectin, the alpha-anomer of the methyl glycoside is only a little more effective as an inhibitor than the beta-anomer and the most potent inhibitor was 9-deoxy-10-carboxylic acid Neu5Ac, followed by 4-oxo-Neu5Ac. In contrast to the majority of known sialic acid-binding lectins, the N-acetyl group of Neu5Ac is not indispensable for binding, neither is the hydroxyl group at C-9 since substitutions at this carbon atom are well tolerated. Furthermore, all sulfur-containing substituents at C-9 enhanced the affinity of the lectin. This is the first sialic acid-binding lectin found to strongly bind thio derivatives.

Blood group antigen expression in the rat colon I. age-dependent and region-related changes

The blood group antigens H, A, B, and Le(b) are oncofetal antigens of the human distal colon. Although these antigens are present in the digestive mucosa of the rat, little is known about their ontogenic expression in the developing rat colon. The present study was undertaken to assess age-dependent and region-related changes of blood group antigens during colonic development and maturation with the aim of determining their fetal phenotype. Antigen expression was assessed by immunohistochemistry using H-, A-, B-, Le(a)-, and Le(b)-specific monoclonal antibodies and formalin-fixed, paraffin-embedded colon sections from fetal, suckling, weanling, and adult rats. Staining of antigen was analyzed with respect to its locations in colonic goblet cells, brush borders, and columnar cells. H, B, and Le(b) antigens were expressed by goblet cells of the distal colon, beginning at 20 days of gestation, but expression was lost from the colon during the first postnatal week, thus exhibiting a fetal phenotype. H and Le(b), but not B, were also expressed by goblet cells of the fetal proximal colon; however, unlike that of the distal colon, their expression increased progressively during postnatal development until adulthood. Fetal phenotypic expression was observed in the brush border of the proximal and distal colon for H antigen, whereas it was observed in that of the distal colon for B antigen. No fetal phenotypic expression of H, B, and Le(b) by columnar cells of the colon was observed. Antigen A was expressed by goblet cells, brush border, and columnar cells of the entire colon at all ages, in concert with the development and maturation of the colon. Therefore, its expression in the rat colon was not fetal in nature. Le(a) was not detected in the colon at any age, except for some sporadic staining in the Golgi zone of columnar cells of the postnatal proximal colon. In conclusion, these data indicate significant age- and region-related changes of blood group antigen expression in the rat colon. Because the fetal phenotypic expression of H, B, and Le(b) by goblet cells of the distal colon mimics that in the human distal colon, the adult rat colon is a potentially useful model for assessing the effects of cocarcinogenic dietary factors, including ethanol, that may induce reexpression of these so-called oncofetal tumor-associated antigens of the colon.

Fatores antinutricionais: inibidores de proteases e lectinas

Os fatores antinutricionais presentes em alimentos podem provocar efeitos fisiológicos adversos ou diminuir a biodisponibilidade de nutrientes. A maior questão sobre os riscos à saúde provocados por antinutrientes é o desconhecimento dos níveis de tolerância, do grau de variação do risco individual e da influência de fatores ambientais sobre a capacidade de detoxificação do organismo humano. Dentre os fatores antinutricionais os inibidores de proteases e as lectinas são considerados instáveis ao tratamento térmico. A hipertrofia pancreática causada pelos inibidores de tripsina tem sido relatada em alguns estudos com animais. As alterações da função fisiológica em animais causadas por ação de lectinas no intestino parecem estar relacionadas à especificidade destas substâncias com as células da mucosa intestinal. Os possíveis efeitos adversos dos inibidores de proteases e das lectinas na maioria das vezes são inferidos somente de experimentos com animais de laboratório.

Interferon beta-1a prevents the effects of lipopolysaccharide on embryonic brain microvessels

By means of light and electron microscopy we have studied the effect of interferon beta-1a (IFNbeta-1a) in the optic tecta of 20-day-old chick embryos under normal conditions and after exposure to lipopolysaccharide (LPS) which mimics the blood-brain barrier (BBB) disruption in meningoencephalitis. Optic tecta were examined for: (i) ultrastructure by means of transmission electron microscopy; (ii) the immunohistochemical localization of HT7 antigen, a specific marker of differentiation of the brain microvessels; (iii) the brain microvessel permeability, by means of horseradish peroxidase (HRP) tracer; (iv) the expression of microvessel glycoconjugates, by means of lectin histochemistry, using Ricinus communis agglutinin-I (RCA-I), specific for beta-D-galactosyl moieties and Wheat Germ agglutinin (WGA) specific for sialyl and N-acetylglucosaminyl moieties. A morphometric evaluation of brain microvessel permeability and of glycoconjugate expression was also performed. In control- and in IFNbeta-1a-treated embryos, HRP was confined to the vessel lumina which were sealed by the interendothelial tight junctions. RCA-I binding sites were recognizable both in the basal membranes and in the tight junctions, while WGA sites were present on the luminal side of the endothelial cells. HRP was blocked in the vessels lumina by the interendothelial tight junctions. After LPS treatment, HRP showed an extravascular localization and the labeling of microvessels by anti-HT7 antibodies disappeared. RCA-I binding was only found ultrastructurally and appeared as irregularly clustered gold particles, in the cleft of damaged tight junctions, but were no longer detectable in the endothelial basement membranes. After pretreatment of LPS-treated embryos with IFNbeta-1a, the vessel permeability to HRP strongly decreased and the vessels showed the normal pattern of HT7 protein and of the RCA-I binding sites. These results indicate that the changes induced by LPS in the endothelial cells are prevented by IFNbeta-1a.

Membrane redistribution of the Escherichia coli MinD protein induced by MinE

Escherichia coli cells contain potential division sites at midcell and adjacent to the cell poles. Selection of the correct division site at midcell is controlled by three proteins: MinC, MinD, and MinE. It has previously been shown (D. Raskin and P. de Boer, Cell 91:685-694, 1997) that MinE-Gfp localizes to the midcell site in an MinD-dependent manner. We use here Gfp-MinD to show that MinD associates with the membrane around the entire periphery of the cell in the absence of the other Min proteins and that MinE is capable of altering the membrane distribution pattern of Gfp-MinD. Studies with the isolated N-terminal and C-terminal MinE domains indicated different roles for the two MinE domains in the redistribution of membrane-associated MinD.

Digestive System 1

This chapter deals with the digestive system. The major and minor salivary glands and their secretions also represent and integral part of the protective mechanism of the oral cavity, and derangement of saliva production may lead to loss of integrity of the oral mucosa. Drug-induced abnormalities of taste sensation are also well-described phenomena occurring in man although human studies are necessary for the detection of these effects. Inflammation of the oral cavity may involve the buccal mucosa, the gingiva (gingivitis), the tongue (glossitis), and the peridontal tissues (peridontitis). Therapeutic agents can induce inflammatory lesions in the tongue. Moreover, a protective layer of mucus, a visco-elastic material containing high molecular weight glycoproteins produced by the major and minor salivary glands, covers the stratified squamous mucosa of the oral cavity. Salivary secretions also possess digestive enzyme activity although in herbivores and carnivores, it is usually low in contrast to high digestive enzyme activity in omnivorous species.

A putative role for carbohydrates in sea urchin gastrulation

Many studies have examined the effects of lectins on embryonic development. Recently, it has been shown that lectins actually enter the blastocoel of sea urchin embryos without microinjection and bind to specific cell types. The present study was performed to examine the effects of lectins on sea urchin gastrulation. Strongylocentrotus purpuratus sea urchin embryos were incubated with several lectins at concentrations from 0.01 microgram/ml to 100 micrograms/ml at 15-28 h in the presence or absence of the preferential binding sugars. The most interesting findings were that the mannose specific lectins Lens culinaris agglutinin (LcH) which binds to secondary mesenchyme cells involved in archenteron anchoring and Pisum sativum (PSA) caused exogastrulation. Wheat germ agglutinin (WGA) which binds to primary mesenchyme cells involved in skeletogenesis caused defective skeletogenesis. Our findings suggest that D-mannose-like residues (LcH and PSA specific sugar) may function in archenteron development and anchoring, while N-acetyl-D-glucosamine-like groups (WGA specific sugar) may contribute to control of primary mesenchyme positioning and function. Specific carbohydrate-containing receptors may, therefore, be of importance in specific gastrulation events.

Carcinogenesis and the plasma membrane

Presented is a two-stage hypothesis of carcinogenesis based on: (1) plasma membrane defects that produce abnormal electron and proton efflux; and (2) electrical uncoupling of cells through loss of intercellular communication. These changes can be induced by a wide variety of stimuli including chemical carcinogens, oncoviruses, inherited and/or acquired genetic defects, and epigenetic abnormalities. The resulting loss of electron/proton homeostasis leads to decreased transmembrane potential, electrical microenvironment alterations, decreased extracellular pH, and increased intracellular pH. This produces a positive feedback loop to enhance and sustain the proton/electron efflux and loss of intercellular communication. Low transmembrane potential is functionally related to rapid cell cycling, changes in membrane structure, and malignancy. Intracellular alkalinization affects a variety of pH-sensitive systems including glycolysis, DNA synthesis, DNA transcription and DNA repair, and promotes genetic instability, accounting for the accumulation of genetic defects seen in malignancy. The abnormal microenvironment results in the selective survival and proliferation of malignant cells at the expense of contiguous normal cell populations.

Effects of wheat germ agglutinin on tunicate egg activation and fertilization: is there a plasma membrane sperm receptor system on Ascidia ceratodes eggs?

Little work has been carried out on the sperm recognition systems present on the egg plasma membrane. Here it is shown that wheat germ agglutinin (WGA) interferes with the sperm-interacting system on the plasma membrane of eggs of the ascidian, Ascidia ceratodes. The WGA activates the dechorionated egg, indicating that a plasma membrane sugar residue can be directly tied to egg activation. Low concentrations of this lectin do not activate the eggs, but reduce fertilizability. This observation suggests that the WGA binding site might be part of a sperm reception-activation complex in the plasma membrane. While WGA also affects sperm binding to the chorion, the mechanisms of sperm interaction at the plasma membrane and chorion show different sensitivities to lectins, sugars and enzymes.

Carbohydrate induced modulation of cell membrane VII. Binding of exogenous lectin increases osmofragility of erythrocytes

Due to their multivalent binding character, lectins when added exogenously will cross-link membrane surface receptors leading to lateral molecular reorganizations in the plane of the bilayer. This study reports for the first time that agglutination of rabbit erythrocytes by lentil lectin and concanavalin A increases their osmofragility. Increase in osmofragility was detected by measuring the hemolysis of erythrocytes in hypotonic as well as in isotonic solutions. It was also found that agglutination per se does not increase osmofragility but the binding of legume lectin is essential since human Rh+ cells agglutinated by a monoclonal antibody do not exhibit hemolysis.