Lectins: Models of Natural and Induced Molecules in Invertebrates

Biomarker responses in terrestrial gastropods exposed to pollutants: A comprehensive review

The chemical contamination of terrestrial ecosystems is a great concern as these ecosystems are the target of most of the pollutants derived from anthropogenic activities such as pesticides, heavy metals, nanoparticles, and others. Terrestrial gastropods are considered to be excellent sentinel organisms for biological monitoring of environmental pollution, as they have the ability to accumulate chemicals in their tissues and exhibit a great potential to evaluate the ecological effects of pollutants in terrestrial ecosystems. The use of biomarkers as sensitive parameters to estimate the exposure or resulting effects of chemicals have received considerable attention. The successful biomarker must be applicable in the laboratory and field conditions. Many biomarkers have been examined to understand the adverse effects of pollutants. In this review, we shed light on different types of biomarkers, such as oxidative stress, genotoxicity and immunotoxicity as diagnostic tools for monitoring the impacts of pollution. These biomarkers can provide information about early detection and quantification of these impacts during their initial manifestations and can facilitate the implementation of a rapid preventive and/or restorative responses in the affected ecosystems, as well as single or multiple biomarkers can be integrated into routine monitoring programs.

Ecotoxicological biomarkers as investigating tools to evaluate the impact of acrylamide on Theba pisana snails

Acrylamide (ACR) is a widespread industrial chemical with recognized adverse effects not only to humans but to other organisms in the environment as well. In the present study, the ecotoxicological effects of dietary exposure to sublethal concentration (1/20 LC₅₀) of ACR on the land snail, Theba pisana after 2 weeks of exposure and 1-week recovery with respect to oxidative stress parameters; lipid peroxidation (LPO), reduced glutathione (GSH), catalase (CAT), and glutathione-S-transferase (GST), cytogenetic parameter; deoxyribonucleic acid (DNA) content, as well as immunological parameters; cell death, phagocytosis, lysosomal membrane stability (LMS), lectins, superoxide anion (O₂^-) generation, phenoloxidase (PO), peroxidase (POD), and hemocyanin (Hc) were examined. The results showed that ACR significantly increased LPO level and the activity of CAT and GST, cell death, and Hc level, whereas a significant decline in DNA and GSH contents, phagocytic activity, LMS, lectins, O₂^- generation, POD, and PO activities compared to the controls after 2-week exposure was observed. After 1-week recovery, most of the tested parameters in exposed snails were permanent and not reversible to the control levels. This study suggests that the tested multiple parameters of T. pisana species may be used as biomarkers of ACR exposure. Besides, T. pisana snails could be used as a good sentinel organism for ACR exposure in pollution monitoring studies.

Purification and characterization of a T-antigen specific lectin from the coelomic fluid of a marine invertebrate, sea cucumber (Holothuria scabra)

A novel lectin was purified from the coelomic fluid of the sea cucumber Holothuria scabra (HSL), subjected to bacterial challenge. HSL is a monomeric glycoprotein of molecular mass 182 kDa. The lectin is highly thermostable as it retains full activity for 1 h at 80 degrees C. Further, the hemagglutination activity of HSL is unaffected by pH in the range 2-11. Unlike other lectins purified from marine invertebrates, the hemagglutination activity of HSL does not require any divalent metal ions. The affinity profile of HSL was studied by a combination of hemagglutination inhibition and fluorescence spectroscopy. HSL binds to desialylated glycoproteins, MealphaGal, T-antigen and T (alpha-ser)-antigen with a distinction between beta1-4 and beta1-3 linkages. Mealpha-T-antigen was a potent ligand having highest affinity (Ka 8.32 x 10(7)M(-1)). Monosaccharide binding is enthalphically driven while disaccharide binding involves both entropic and enthalpic contributions.

Tick lectins: structural and functional properties

Few papers have been published on tick lectins so far, and therefore more data are needed to complete the mosaic of knowledge of their structural and functional properties. Tissue-specific lectin/haemagglutinin activities of both soft and hard ticks have been investigated. Some tick lectins are proteins with binding affinity for sialic acid, various derivatives of hexosamines and different glycoconjugates. Most tick lectin/haemagglutinin activities are blood meal enhanced, and could serve as molecular factors of self/non-self recognition in defence reactions against bacteria or fungi, as well as in pathogen/parasite transmission. Dorin M, the plasma lectin of Ornithodoros moubata, is the first tick lectin purified so far from tick haemolymph, and the first that has been fully characterized. Partial characterization of other tick lectins/haemagglutinins has been performed mainly with respect to their carbohydrate binding specificities and immunochemical features.

Characterization of lectin aggregates in the hemolymph of freshwater prawn Macrobrachium rosenbergii

In invertebrates, lectins play relevant roles in innate immunity; however, their regulatory mechanisms have not been identified yet. In this work, we purified, by gel filtration and affinity chromatography, lectin aggregates circulating in the hemolymph of the freshwater prawn Macrobrachium rosenbergii and compared their physicochemical properties with a previously described lectin (MrL). High-molecular weight MrL aggregates (MrL-I) lack hemagglutinating activity and showed bands of 62.1, 67.1 and 81.4 kDa, whereas MrL-III, which corresponds to MrL, showed hemagglutinating activity and is constituted by a single 9.6-kDa band as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. MrL-I and MrL-III showed similar amino acid composition but different carbohydrates concentration. Edman degradation indicated NH2-terminal sequence of five amino acids for the 9.6-kDa MrL-III (DVPLL/A) and eleven for the main 81.4-kDa band identified in MrL-I (DVPLL/AXKQQQD); analysis by MALDI-TOF indicated a different tryptic pattern for MrL-I and MrL-III. MrL-I was recognized by monoclonal antibodies against MrL-III. Circular dichroism indicated that the secondary structure in both proteins is similar and contains 23% of beta-sheet and 24% of alpha-helix. Our results suggest that differential posttranslational processes that favor aggregation are involved in regulating the activity of the lectin.

Bacterial colonisation in the gut of Phlebotomus duboseqi (Diptera: Psychodidae): transtadial passage and the role of female diet

Bacteria isolated from the gut of different developmental stages of Philebotomus duboseqi Neveu-Lcmaire, 1906 belonged almost all to aerobic or facultatively anaerobic gram-negative rods. In females, the highest bacterial counts were observed two days after bloodfeeding; seven days after bloodfeeding the bacterial counts returned to pre-feeding levels. Most isolates were identified phenotypically as Ochrobactrum sp. The distinctiveness and homogeneity of the phenotypic and genotypic characteristics of Ochrobactrum isolates indicated that they belonged to a single strain (designated AK). This strain was acquired by larvae from food and passaged transtadially: it was isolated from the guts of fourth-instar larvae shortly before pupation, from pupae as well from newly emerged females. Most other bacteria found in females were acquired from the sugar solution fed to adults. To determine if the midgut lectin activity may serve as antibacterial agent females were membrane-fed on blood with addition of inhibitory carbohydrates. No significant differences in bacterial infections were found between experimental and control groups and we suppose that the lectin activity has no effect on gram-negative bacteria present in sandfly gut.

Characterization and partial purification of a lectin from the hemolymph of the white shrimp Litopenaeus schmitti

The agglutinating activity of the hemolymph of Litopenaeus schmitti is insensitive to calcium and specific for acetylated sugars, particularly sialic acid (Neu5Ac) and O-sialoglycoconjugates (bovine submaxillary mucin) and has varying specificity for different LPS, which may suggest a putative role in microorganism recognition. Affinity chromatography on fetuin-agarose of the agglutinin resulted in a 220 kDa band (lectin), and a 82.5 kDa band, which probably is hemocyanin. The 220 kDa protein consists of 31 and 34 kDa subunits, suggesting that this lectin is multimeric. The lectin molecular mass was estimated by gel filtration to be 153+/-10 kDa. The hemolymph of L. schmitti comprises at least another soluble lectin, with distinct chemical and carbohydrate specificity than the 220 kDa lectin.

Quantification of lectin in freshwater prawn (Macrobrachium rosenbergii ) hemolymph by ELISA

An enzyme-linked immunoabsorbent assay was developed to quantify the lectin present in the hemolymph of the freshwater prawn Macrobrachium rosenbergii. This method involves the use of murine monoclonal IgG1 with kappa light chain (designated as 3G1) antibodies raised against the purified lectin, the assay that we developed recognized as little as 30 ng/ml of lectin, and was used to measure the lectin concentration in animals at different maturation stages. The highest concentration of lectin was identified in the hemolymph from post-larval prawns and the lowest in molt stage adult animals. The hemagglutination activity of the lectin was four-fold higher in adult than in juvenile specimens, although in all cases N-acetylated sugar residues, such as N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, and N-acetyl-D-neuraminic acid were inhibitors of the lectin activity, suggesting that lectin plays a role in the transport of N-acetylated sugar in juvenile prawns. Our results indicate that lectin concentration and hemagglutinating activity could be influenced by developmental conditions of the freshwater prawn.

Isolation and characterization of Dorin M, a lectin from plasma of the soft tick Ornithodoros moubata

A lectin with high hemagglutinating activity, which we have named Dorin M, was identified in the plasma of the soft tick Ornithodoros moubata. The activity of the plasma lectin could be efficiently inhibited by sialic acid, N-acetyl-D-hexosamines and sialoglycoproteins. Dorin M was purified to homogeneity using two different isolation systems: affinity chromatography on a column of bovine submaxillary mucin conjugated to Sepharose 4B with specific elution by N-acetyl-D-glucosamine and chromatography on Blue-Sepharose followed by anion exchange FPLC on a MonoQ column. The purified lectin is a glycoprotein which, in the native state, forms aggregates with molecular mass of about 640 kDa. Non-reducing SDS PAGE revealed that the lectin consists of two noncovalently bound subunits migrating closely around 37 kDa. Dorin M is a glycoprotein, probably modified by N-type glycosylation. After chemical deglycosylation, only one band of about 32 kDa was detected. Dorin M is the first lectin purified from ticks.

Evolution of the innate and adaptive immune systems: relationships between potential immune molecules in the lowest metazoan phylum (Porifera) and those in vertebrates

Porifera (sponge) form the lowest metazoan phylum and share a common ancestor with other metazoan phyla. In the present study, it is reported that sponges possess molecules that are similar in structure to those molecules involved in the immune system in mammals. Experiments with the marine sponges Geodia cydonium and Suberites domuncula have been performed on tissue (auto- and allografting) as well as on a cellular level. The studies revealed that sponges are provided with elements of the mammalian innate immune system, such as molecules containing scavenger receptor cysteine-rich domains. Furthermore, macrophage-derived cytokine-like molecules have been identified that are up-regulated during the grafting process. In addition, the (2'-5')oligoadenylate synthetase system exists in sponges. "Precursors" of the second type of immune response in mammals, the adaptive immune system, have been traced in sponges. It is shown that the expression of a lymphocyte-derived cytokine from mammals is up-regulated during non-self-recognition in S. domuncula. Finally, in G. cydonium, two classes of receptors that comprise Ig-like domains have been identified: the receptor tyrosine kinases and the non-enzymic sponge adhesion molecules. They contain two polymorphic Ig-like domains that are grouped to the variable set of immunoglobulins. The expression of these molecules is also up-regulated during the grafting process. It is concluded that sponges are already provided with a series of elements used in higher vertebrates for both the innate and the adaptive immune recognition.

Identification and cloning of a glucan- and lipopolysaccharide-binding protein from Eisenia foetida earthworm involved in the activation of prophenoloxidase cascade

Coelomic fluid of Eisenia foetida earthworms contains a 42-kDa protein named coelomic cytolytic factor 1 (CCF-1) that was described previously to be involved in cytolytic, opsonizing, and hemolytic properties of the coelomic fluid. Cloning and sequencing of CCF-1 reveal significant homology with the putative catalytic region of beta-1,3- and beta-1,3-1,4-glucanases. CCF-1 also displays homology with coagulation factor G from Limulus polyphemus and with Gram-negative bacteria-binding protein of Bombyx mori silkworm, two proteins involved in invertebrate defense mechanisms. We show that CCF-1 efficiently binds both beta-1,3-glucan and lipopolysaccharide. Moreover, CCF-1 participates in the activation of prophenoloxidase cascade via recognition of yeast and Gram-negative bacteria cell wall components. These results suggest that the 42-kDa CCF-1 protein of E. foetida coelomic fluid likely plays a role in the protection of earthworms against microbes.

Sialic acid in hemolymph and affinity purified lectins from two marine bivalves

Sialic acids have been implicated in a variety of complex biological regulatory and signalling events and their functional importance is reflected by their presence in a wide variety of phyla. Potentially they may inhibit intermolecular and intercellular interactions. Lectins that exhibit specificity for sialic acid or sialoglycoconjugates are ubiquitous in the body fluids of invertebrates and this has supported the assumption that these lectins are involved in defense against microbes that express sialic acids on their surfaces. This biological function has also been inferred from the absence of sialic acids in lower invertebrates. However, most invertebrate lectins are heterogeneous and may also bind other ligands. The biological significance of the different carbohydrate specificities are not yet known. We have demonstrated the presence of sialic acids in hemolymph from two marine bivalves, the Pacific oyster Crassostrea gigas (approximately 15 micrograms ml-1) and the horse mussel Modiolus modiolus (48-100 micrograms ml-1) by several different assays. The sialic acid was mostly in free form. Affinity purified lectins from the horse mussel also contained bound sialic acids (2-5 mumol g-1). Oyster hemolymph stimulated the in vitro phagocytosis of bacteria by oyster hemocytes. The stimulation by hemolymph is facilitated by a dialyzable component, that apparently is active irrespective of the binding to sialic acid (BSM). Addition of sialic acid had no significant effect on the in vitro phagocytosis of bacteria by oyster hemocytes.

Sialic acid-binding lectin with antibacterial activity from the horse mussel: further characterization and immunolocalization

A heterogeneous sialic acid-binding lectin with affinity for bacterial LPS was isolated and partially characterized from hemolymph of the horse mussel Modiolus modiolus.(1) Using two-dimensional electrophoresis with immobilized pH gradients, the lectin revealed three subunits with different molecular weight and isoelectric points (pI); Mr14 (pI approximately 5.1 and approximately 5.5), 17.5 (pI approximately 5.5) and 20 (pI approximately 4.9) kDa. The affinity purified lectin existed in its native state as aggregates, and by stepwise centrifugation it could be fractionated into molecular entities with distinct specificities towards human and/or horse erythrocytes (modiolin H and/or E activity, respectively). While the medium size entities (range < or = 30 and < 100 kDa) exhibited only modiolin E activity and the lowest size entities (range < or = 5 and < 10 kDa) demonstrated only modiolin H activity, the largest aggregates (> or = 100 kDa-)expressed both activities. Antibacterial activity of the lectin has been observed against various marine bacteria, whereas the whole hemolymph was less effective. The lectin exhibited strong antibacterial effect against all tested strains of Vibrio anguillarum, Vibrio salmonicida, Vibrio viscosus, Vibrio wodanis, and Vibrio ordalii, slight effect on Aeromonas salmonicida salmonicida and Shewanella putrefaciens, and no inhibitory effect with Alteromonas sp. Hemolymph of the horse mussel demonstrated no antibacterial effect against A. salmonicida salmonicida, Alteromonas sp., Sh. putrefaciens and some strains of V. anguillarum, but slight effects against some strains of V. anguillarum and both strains of V. ordalii, and more predominantly against V. wodanis, V. salmonicida and V. viscosus. These results indicate that the lectin plays a role in elimination of bacteria. Circulating hemocytes were demonstrated to be the source of the lectins since granules of the hemocytes were immunoreactive to anti-hemolymph lectin antibody and protein A/gold labelling.

A heterogeneous sialic acid-binding lectin with affinity for bacterial LPS from horse mussel (Modiolus modiolus) hemolymph

A sialic acid-binding lectin that agglutinates a variety of erythrocytes and bacteria and react with sialoconjugates and purified lipopolysaccharides from marine vibrios has been affinity purified from hemolymph of the horse mussel Modiolus modiolus using Bovine submaxillary mucin conjugated to CNBr-activated Sepharose 4B. The lectin demonstrated heterogeneous activity, and at least two main entities were partially characterized, and are referred to as modiolin H and modiolin E activities for the agglutination of human and horse (equine) erythrocytes, respectively. Only modiolin E activity required calcium ions for hemagglutination. The M. modiolus lectin was mainly specific for NeuAc, although the lectin demonstrated a broader range of specificity, similarly to the Limulus polyphemus lectin. The purified lectin was a glycoprotein, and in the native state existed as aggregates with M(r) in the range of 100-1,300 kDa as observed by gradient-gel electrophoresis and gel filtration on Biogel and Superose. SDS-PAGE under reducing conditions revealed three subunits of M(r) 14, 17.5 and 20 kDa. Various marine bacteria adsorbed the hemagglutinating activities of the M. modiolus lectin. Purified LPS preparations from various pathogenic marine vibrios were also effective inhibitors, in particular for modiolin E activity. These results indicate that the lectin play a role in recognition of bacteria.