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

Transcriptome sequencing reveals improved ammonia nitrogen tolerance in Zebra II strain of the Manila clam Ruditapes philippinarum

In this research, we identified genes associated with ammonia nitrogen (TAN) stress response and resistance in juveniles of the Zebra II strain and a wild population of the Manila clam Ruditapes philippinarum. Both groups were subjected to a 96 h acute toxicity test using TAN concentrations of 17.617 ± 0.634 and 16.670 ± 0.7 mg/l, respectively. We then collected samples, conducted transcriptome sequencing and screened the sequences for differentially expressed genes (DEGs) related to TAN stress response. We identified 2908 and 2861 DEGs in the Zebra II and wild clam groups, respectively, and the two groups had 626 DEGs in common. The verified DEGs had less of a detoxification effect in the wild population than that in the Zebra II group. Gene Ontology database analysis showed that Zebra II juveniles were mainly enriched in protein phosphorylation, purine nucleoside binding, and kinase activity, whereas the wild population juveniles were primarily enriched in oxidases activity, organic acid metabolic processes, and extracellular regions. Kyoto Encyclopedia of Genes and Genomes pathway analysis mainly highlighted aminoacyl tRNA biosynthesis in Zebra II juveniles and sphingolipid metabolism, FOXO signaling, biosynthesis of aminoacyl tRNA, and other pathways in the wild population. These results show that the toxic effect of TAN on the Manila clam is related to a variety of pathways, which are mainly related to immune response, inflammatory response, metabolic pathways, and nerve conduction. This study provides basic data and theoretical reference for revealing the molecular regulation mechanism of the improved TAN tolerance of Zebra II strain as compared with the wild population of Ruditapes philippinarum.

An Update of Lectins from Marine Organisms: Characterization, Extraction Methodology, and Potential Biofunctional Applications

Lectins are a unique group of nonimmune carbohydrate-binding proteins or glycoproteins that exhibit specific and reversible carbohydrate-binding activity in a non-catalytic manner. Lectins have diverse sources and are classified according to their origins, such as plant lectins, animal lectins, and fish lectins. Marine organisms including fish, crustaceans, and mollusks produce a myriad of lectins, including rhamnose binding lectins (RBL), fucose-binding lectins (FTL), mannose-binding lectin, galectins, galactose binding lectins, and C-type lectins. The widely used method of extracting lectins from marine samples is a simple two-step process employing a polar salt solution and purification by column chromatography. Lectins exert several immunomodulatory functions, including pathogen recognition, inflammatory reactions, participating in various hemocyte functions (e.g., agglutination), phagocytic reactions, among others. Lectins can also control cell proliferation, protein folding, RNA splicing, and trafficking of molecules. Due to their reported biological and pharmaceutical activities, lectins have attracted the attention of scientists and industries (i.e., food, biomedical, and pharmaceutical industries). Therefore, this review aims to update current information on lectins from marine organisms, their characterization, extraction, and biofunctionalities.

A Novel C1q Domain-Containing Protein Isolated from the Mollusk Modiolus kurilensis Recognizing Glycans Enriched with Acidic Galactans and Mannans

C1q domain-containing (C1qDC) proteins are a group of biopolymers involved in immune response as pattern recognition receptors (PRRs) in a lectin-like manner. A new protein MkC1qDC from the hemolymph plasma of Modiolus kurilensis bivalve mollusk widespread in the Northwest Pacific was purified. The isolation procedure included ammonium sulfate precipitation followed by affinity chromatography on pectin-Sepharose. The full-length MkC1qDC sequence was assembled using de novo mass-spectrometry peptide sequencing complemented with N-terminal Edman's degradation, and included 176 amino acid residues with molecular mass of 19 kDa displaying high homology to bivalve C1qDC proteins. MkC1qDC demonstrated antibacterial properties against Gram-negative and Gram-positive strains. MkC1qDC binds to a number of saccharides in Ca2+-dependent manner which characterized by structural meta-similarity in acidic group enrichment of galactose and mannose derivatives incorporated in diversified molecular species of glycans. Alginate, κ-carrageenan, fucoidan, and pectin were found to be highly effective inhibitors of MkC1qDC activity. Yeast mannan, lipopolysaccharide (LPS), peptidoglycan (PGN) and mucin showed an inhibitory effect at concentrations three orders of magnitude greater than for the most effective saccharides. MkC1qDC localized to the mussel hemal system and interstitial compartment. Intriguingly, MkC1qDC was found to suppress proliferation of human adenocarcinoma HeLa cells in a dose-dependent manner, indicating to the biomedical potential of MkC1qDC protein.

Sialic acid and biology of life: An introduction

Sialic acids are important molecule with high structural diversity. They are known to occur in higher animals such as Echinoderms, Hemichordata, Cephalochorda, and Vertebrata and also in other animals such as Platyhelminthes, Cephalopoda, and Crustaceae. Plants are known to lack sialic acid. But they are reported to occur in viruses, bacteria, protozoa, and fungi. Deaminated neuraminic acid although occurs in vertebrates and bacteria, is reported to occur in abundance in the lower vertebrates. Sialic acids are mostly located in terminal ends of glycoproteins and glycolipids, capsular and tissue polysialic acids, bacterial lipooligosaccharides/polysaccharides, and in different forms that dictate their role in biology. Sialic acid play important roles in human physiology of cell-cell interaction, communication, cell-cell signaling, carbohydrate-protein interactions, cellular aggregation, development processes, immune reactions, reproduction, and in neurobiology and human diseases in enabling the infection process by bacteria and virus, tumor growth and metastasis, microbiome biology, and pathology. It enables molecular mimicry in pathogens that allows them to escape host immune responses. Recently sialic acid has found role in therapeutics. In this chapter we have highlighted the (i) diversity of sialic acid, (ii) their occurrence in the diverse life forms, (iii) sialylation and disease, and (iv) sialic acid and therapeutics.

Sialic acid-binding lectins (SABLs) from Solen grandis function as PRRs ensuring immune recognition and bacterial clearance

Sialic acid-binding lectins (SABLs) are ubiquitous ancient molecules with binding properties to N-acetyl or N-glycolyl carbohydrates, and play crucial roles in both adaptive and innate immune responses. In present study, recombinant protein and antibodies of two SABLs from mollusk Solen grandis (SgSABL-1 and SgSABL-2) were prepared to investigate their functions in innate immunity. The recombinant protein of SgSABL-1 (rSgSABL-1) could bind LPS, PGN and β-glucan in vitro, while rSgSABL-2 could only bind PGN rather than LPS and β-glucan. Be coincident with their PAMPs recognition properties, rSgSABL-1 displayed a broad agglutination spectrum towards gram-positive bacteria Micrococcus luteus, gram-negative bacteria Listonella anguillarum and fungi Pichia pastoris, and rSgSABL-2 only showed remarkable agglutinative effect on M. luteus and L. anguillarum. More importantly, after PAMPs recognition, rSgSABL-1 and rSgSABL-2 enhanced phagocytosis as well as encapsulation ability of hemocytes in vitro, and the enhanced encapsulation could be blocked by specific antibodies. All these results indicated that SgSABL-1 and SgSABL-2 functioned as two compensative pattern-recognition receptor (PRRs) with distinct recognition spectrum and involved in the innate immune response of S. grandis.

Gal/GalNAc specific multiple lectins in marine bivalve Anadara granosa

Complete lectin mapping of molluscs with their diversified recognition pattern and possible role in lectin-carbohydrate interaction based immune response triggering need much attention. In this communication, Gal/GalNAc specific three lectins AGL-IA (Anadara granosa lectin-IA), AGL-IB (A. granosa lectin-IB) and AGL-IV (A. granosa lectin-IV) and a lectin having hemolytic activity AGL-III (A. granosa lectin-III) were purified from the plasma of A. granosa bivalve by a combination of gel filtration and affinity chromatography. AGL-IA and IB were oligomeric lectins whereas, AGL-III and IV were monomeric. The molecular weight of AGL-IA, IB, III and IV were 375, 260, 45 and 33 kDa respectively. AGL-IA and IV agglutinated both rabbit and pronase treated human erythrocytes, whereas AGL-IB agglutinated only rabbit erythrocytes. AGL-III was found to agglutinate rabbit erythrocytes, however, it caused hemolysis of pronase treated human erythrocytes. The activity of all four lectins was calcium dependent and maximum at a pH range 7-8. Apart from Gal/GalNAc specific, the four lectins showed substantial differences in their carbohydrate recognition pattern. Moreover, there was a difference in the carbohydrate specificity between AGL-III and other three lectins (AGL-IA, AGL-IB and AGL-IV) towards polyvalent glycotope. On the one hand, 'cluster glycoside effect' i.e., an enhancement of the activity of a multivalent ligand, was observed for carbohydrate specificities of AGL-IA, AGL-IB, AGL-IV. On the other hand, the effect of multivalent ligands on the carbohydrate specificity of AGL-III was opposite of cluster glycoside effect. The affinity of AGL-IA, AGL-IB and AGL-IV for ligands can be ranked as follows: glycoproteins >> polysaccharide > oligosaccharides and monosaccharides. However, Gal related monosaccharides were the best inhibitors of AGL-III and the inhibitory activity decreased gradually in the following order: monosaccharide > disaccharide > polysaccharide. Thus, the diverse specificity of multiple lectins in A. granosa plasma possibly enables to recognize a wide range of microorganisms.

Proteomic characterization of mucosal secretions in the eastern oyster, Crassostrea virginica

The soft body surface of marine invertebrates is covered by a layer of mucus, a slippery gel secreted by mucocytes lining epithelia. The functions of this gel are diverse including locomotion, cleansing, food particles processing and defense against physicochemical injuries and infectious agents. In oysters, mucus covering pallial organs has been demonstrated to have a major importance in the processing of food particles and in the interactions with waterborne pathogens. Given the limited information available on mucus in bivalves and the apparent wide spectra of activity of bioactive molecules present in this matrix, the characterization of these mucosal secretions has become a research priority. In this study, mucus was separately collected from the mantle, gills and labial palps of the eastern oyster (Crassostrea virginica) and analyzed by liquid chromatography and tandem mass spectrometry. Results showed the presence of a wide variety of molecules involved in host-microbe interactions, including putative adhesion molecules (e.g. c-type lectins) confirming that transcripts previously identified in epithelial cells are translated into proteins secreted in mucus. Mucus composition was different among samples collected from different organs. These results generate a reference map for C. virginica pallial mucus to better characterize the various physiological functions of mucosal secretions.

Lectins of marine hydrobionts

Data from the literature and results of our research on lectins isolated from some kinds of marine hydrobionts such as clams, ascidians, sea worms, sponges, and algae are presented in this review. Results of comparative analysis of the basic physicochemical properties and biological activity of lectins isolated from various sources are discussed.

Purification and characterization of hemagglutinating proteins from Poker-chip Venus (Meretrix lusoria) and Corbicula clam (Corbicula fluminea)

Hemagglutinating proteins (HAPs) were purified from Poker-chip Venus (Meretrix lusoria) and Corbicula clam (Corbicula fluminea) using gel-filtration chromatography on a Sephacryl S-300 column. The molecular weights of the HAPs obtained from Poker-chip Venus and Corbicula clam were 358 kDa and 380 kDa, respectively. Purified HAP from Poker-chip Venus yielded two subunits with molecular weights of 26 kDa and 29 kDa. However, only one HAP subunit was purified from Corbicula clam, and its molecular weight was 32 kDa. The two Poker-chip Venus HAPs possessed hemagglutinating ability (HAA) for erythrocytes of some vertebrate animal species, especially tilapia. Moreover, HAA of the HAP purified from Poker-chip Venus was higher than that of the HAP of Corbicula clam. Furthermore, Poker-chip Venus HAPs possessed better HAA at a pH higher than 7.0. When the temperature was at 4°C–10°C or the salinity was less than 0.5‰, the two Poker-chip Venus HAPs possessed better HAA compared with that of Corbicula clam.

Cloning and characterization of a sialic acid binding lectins (SABL) from Manila clam Venerupis philippinarum

Sialic acid binding lectin (SABL) is a member of immunoglobulin-like lectins family that are thought to promote cell-cell interactions and regulate the functions of cells in the innate and adaptive immune systems through glycan recognition. In the present study, the full-length cDNA of SABL was identified from Manila clam Venerupis philippinarum (denoted as VpSABL) by cDNA library and RACE approaches. The cDNA of VpSABL consisted of a 5'terminal untranslated region (UTR) of 62 bp, a 3' UTR of 354 bp with a poly (A) tail, and an open reading frame (ORF) of 588 bp encoding a polypeptide of 195 amino acids with a typical C1q domain in the C-terminus. Multiple alignment analysis indicated that the deduced amino acid of VpSABL shared higher positive to other SABLs and C1q-contained proteins and should be adopted typical 10 β-strand jelly-roll folding topology common to all C1q-TNF family. Spatial expression analysis indicated that mRNA transcript of VpSABL was predominantly detectable in tissues of mantle, hepatopancreas and gill, and to a lesser degree in the tissues of muscle and haemocytes. After challenged by Vibrio anguillarum, the mRNA level of VpSABL in overall haemocytes population was recorded by quantitative real-time RT-PCR. VpSABL mRNA was down-regulated in the first 24 h post-infection. Then, the expression level increased to the peak at 72 h and recovered to the original level at 96 h. All these results indicated that VpSABL was involved in the immune response against microbe infection and might be contributed to the recognition of bacterial pathogens.

Role of epicellular molecules in the selection of particles by the blue mussel, Mytilus edulis

This study provides evidence that the suspension-feeding blue mussel, Mytilus edulis, uses biochemical cues to recognize its food. We identified lectins in mucus from the gills and labial palps, two pallial organs involved in the feeding process. These compounds were able to agglutinate rabbit and horse erythrocytes (RBC) and several species of marine microalgae representing different families. Additionally, the agglutination of RBC and microalgae was inhibited by several carbohydrates (fetuin, lipopolysaccharide (LPS), and mannose-related residues), suggesting that a suite of lectins may be present in mucus from the gills and labial palps. Results from feeding experiments, using microspheres with tailored surfaces, demonstrated that mussels preferentially ingested microspheres coated with the neoglycoproteins glucosamide-BSA and mannopyranosylphenyl-BSA but rejected in pseudofeces microspheres coated with BSA alone. The positive selection for neoglycoprotein-coated microspheres was inhibited when mussels were pre-incubated in seawater containing a solution of the same neoglycoprotein. Two surface properties of the microspheres, charge and wettability, had little effect on the observed selection process. Our results, along with our previous findings for oysters, suggest a new concept for the mechanism of particle selection in bivalves and perhaps other suspension-feeding organisms. Specifically, the selection of particles involves interactions between epiparticulate carbohydrates and lectins in the mucus produced by feeding organs.

T-antigen binding lectin with antibacterial activity from marine invertebrate, sea cucumber (Holothuria scabra): possible involvement in differential recognition of bacteria

In invertebrates, cellular and humoral components are evolved to maintain their body immunity and integrity. Both these factors respond to different antigens such as microorganisms, vertebrate erythrocytes and foreign proteins. In this article, we report a study of a lectin (HSL) involved in immune response in the echinoderm, sea cucumber (Holothuria scabra). Correlative studies indicate that the expression of this defensive lectin is induced by bacterial challenge, wherein cell wall glycoconjugates of bacteria are involved in lectin induction. HSL showed strong broad spectrum antibacterial activity against both gram-positive and gram-negative bacteria. Under in vitro conditions, purified HSL mediate agglutination of the test bacteria, there by indicating a possible mode of action in physiological situation.

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.

A novel C-type lectin from abalone, Haliotis discus discus, agglutinates Vibrio alginolyticus

Owing to its specific binding to carbohydrates, lectins play important roles in pathogen recognition and clearance in invertebrate animals. In this study, a novel C-type lectin (designated CLHd) gene was isolated from abalone, Haliotis discus discus, cDNA library. The complete cDNA sequence of the CLHd gene is 508 base pairs in length, and encodes 151 amino acids. CLHd shares a highly conserved carbohydrate recognition domain with C-type lectins from mollusk and fish. The mRNA expressions of CLHd in healthy and bacterial-challenged abalones were examined using semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR). CLHd mRNA transcription was up-regulated by Vibrio alginolyticus challenge and reached the maximum expression at 24h after the bacterial injection. To understand its biological activity, the recombinant CLHd gene was constructed and expressed in Escherichia coli. The recombinant CLHd specifically agglutinated V. alginolyticus at a concentration of 50microg/ml in a calcium-dependant way. Both the gene expression analysis and recombinant protein activity assay suggest that CLHd is an important immune gene involved in the recognition and elimination of pathogens in abalones.

Persistence of vibrios in marine bivalves: the role of interactions with haemolymph components

Marine bivalves are widespread in coastal environments and, due to their filter-feeding habit, they can accumulate large numbers of bacteria thus acting as passive carriers of human pathogens. Bivalves possess both humoral and cellular defence mechanisms that operate in a co-ordinated way to kill and eliminate infecting bacteria. Vibrio species are very abundant in coastal waters and are commonly isolated from edible bivalves tissues where they can persist after depuration processes in controlled waters. Such observations indicate that vibrios are regular components of bivalve microflora and that the molluscs can represent an important ecological niche for these bacteria. Here we tried to summarize data on the interactions between vibrios and bivalve haemolymph; the available evidence supports the hypothesis that persistence of bacteria in bivalve tissues depends, at least in part, on their sensitivity to the bactericidal activity of the haemolymph. Results obtained with an in vitro model of Vibrio cholerae challenged against Mytilus galloprovincialis haemocytes indicate that bacterial surface components, soluble haemolymph factors and the signalling pathways of the haemocyte host are involved in determining the result of vibrio-haemolymph interactions.

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.

Bacteria-hemocyte interactions and phagocytosis in marine bivalves

Marine bivalves (such as mussels, oysters, and clams) are widespread mollusks in coastal waters at different latitudes; due to their filter-feeding habits, they accumulate large numbers of bacteria from the harvesting waters and may act as passive carriers of human pathogens. To cope with this challenge, bivalves possess both humoral and cellular defense mechanisms with remarkably effective capabilities. The circulating cells, or hemocytes, are primarily responsible for defense against parasites and pathogens; microbial killing results from the combined action of the phagocytic process with humoral defense factors such as agglutinins (e.g., lectins), lysosomal enzymes (e.g., acid phosphatase, lysozyme), toxic oxygen intermediates, and various antimicrobial peptides. In this work, current knowledge of the mechanisms underlying the interactions between bacteria and the hemolymph components of marine bivalves is summarized. Bacterial susceptibility to hemolymph killing in different bivalve species may be a consequence of the different ability of bacterial products to attract phagocytes, the presence or absence of specific opsonizing molecules, the hemocyte capability to bind and engulf different bacteria, and the different bacterial sensitivity to intracellular killing. The role of soluble (e.g., agglutinins and opsonins) and surface-bound factors in bacterial phagocytosis by hemocytes of the most common marine bivalve species is described and the possibility that environmental temperatures and other seasonal factors may influence this process is considered. Moreover, the potential strategies used by bacteria to evade phagocytic killing by hemocytes are discussed. From the available data it is clear that several questions need further investigation; the elucidation of the factors influencing phagocytosis in bivalves and the fundamental strategies used by bacteria to escape hemolymph killing are important not only to understand bivalve immune defenses but also to explain the persistence of pathogenic bacteria in bivalve tissues and to predict the consequent impact on human health.

Insect cellular reactions to the lipopolysaccharide component of the bacterium Serratia marcescens are mediated by eicosanoids

Nodulation, which begins with the formation of cellular microaggregates, is the predominant cellular defense reaction to bacterial infections in insects. We suggested that these reactions to bacterial infections are mediated by eicosanoids. The lipopolysaccharide (LPS) component of some bacterial cells stimulates defense reactions in mammals and insects. Here, we report on experiments designed to test the hypothesis that eicosanoids mediate microaggregation reactions to LPS. Injections of LPS (purified from the bacterium, Serratia marcescens) into larvae of the tenebrionid beetle, Zophobas atratus, stimulated microaggregation reactions in a dose-dependent manner. Treatments with eicosanoid-biosynthesis inhibitors immediately prior to LPS challenge sharply reduced the microaggregation responses. Separate treatments with specific inhibitors of phospholipase A(2), cyclooxygenase and lipoxygenase reduced microaggregation, supporting our view that microaggregate formation involves lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent within 30min after injection, and microaggregation was significantly reduced, relative to control insects, over the following 90min. The dexamethasone effects were reversed by treating LPS-injected insects with the eicosanoid precursor, arachidonic acid. These findings indicate that cellular defense reactions to a specific component of bacterial cells are mediated by eicosanoids, and open up new possibilities for dissecting detailed hemocytic actions in insect immune reactions to bacterial infections.

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.

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.