A comparison of the Aplysia lectin anti-I specificity with human anti-I and several other I-detecting lectins

Isolation, Amino Acid Sequences, and Plausible Functions of the Galacturonic Acid-Binding Egg Lectin of the Sea Hare Aplysia kurodai

Egg lectins occur in a variety of animals ranging from mollusks to vertebrates. A few examples of molluscan egg lectins have been reported, including that of the sea hare Aplysia kurodai; however, their biological functions in the egg remain unclarified. We report the isolation, determination of primary structure, and possible functions of A.kurodai lectin (AKL) from the egg mass of A. kurodai. We obtained AKL as an inseparable mixture of isoproteins with a relative molecular mass of approximately 32 kDa by affinity purification. The hemagglutinating activity of AKL against rabbit erythrocytes was inhibited most potently by galacturonic acid and moderately by xylose. Nucleotide sequencing of corresponding cDNA obtained by rapid amplification of cDNA ends (RACE) allowed us to deduce complete amino acid sequences. The mature polypeptides consisted of 218- or 219-amino acids with three repeated domains. The amino acid sequence had similarities to hypothetical proteins of Aplysia spp., or domain DUF3011 of uncharacterized bacterial proteins. AKL is the first member of the DUF3011 family whose function, carbohydrate recognition, was revealed. Treatment of the egg with galacturonic acid, an AKL sugar inhibitor, resulted in deformation of the veliger larvae, suggesting that AKL is involved in organogenesis in the developmental stage of A. kurodai.

Differential staining of Western blots of human secreted glycoproteins from serum, milk, saliva, and seminal fluid using lectins displaying diverse sugar specifities

Human milk, serum, saliva, and seminal fluid glycoproteins (gps) nourish and protect newborn and adult tissues. Their saccharides, which resemble cell membrane components, may block pathogen adhesion and infection. In the present study, they were examined by a battery of lectins from plants, animals, and bacteria, using hemagglutination inhibition and Western blot analyses. The lectins included galactophilic ones from Aplysia gonad, Erythrina corallodendron, Maclura pomifera (MPL), peanut, and Pseudomonas aeruginosa (PA-IL); fucose-binding lectins from Pseudomonas aeruginosa (PA-IIL), Ralstonia solanacearum (RSL), and Ulex europaeus (UEA-I), and mannose/glucose-binding Con A. The results demonstrated the chosen lectin efficiency for differential analysis of human secreted gps as compared to CBB staining. They unveiled the diversity of these body fluid gp glycans (those of the milk and seminal fluid being highest): the milk gps interacted most strongly with PA-IIL, followed by RSL; the saliva gps with RSL, followed by PA-IIL and MPL; the serum gps with Con A and MPL, followed by PA-IIL and RSL, and the seminal plasma gps with RSL and MPL, followed by UEA-I and PA-IIL. The potential usage of these lectins as probes for scientific, industrial, and medical purposes, and for quality control of the desired gps is clearly indicated.

Norwalk virus-like particle hemagglutination by binding to h histo-blood group antigens

Noroviruses are a major cause of epidemic acute nonbacterial gastroenteritis worldwide. Here we report our discovery that recombinant Norwalk virus virus-like particles (rNV VLPs) agglutinate red blood cells (RBCs). Since histo-blood group antigens are expressed on gut mucosa as well as RBCs, we used rNV VLP hemagglutination (HA) as a model system for studying NV attachment to cells in order to help identify a potential NV receptor(s). rNV VLP HA is dependent on low temperature (4 degrees C) and acidic pH. Of the 13 species of RBCs tested, rNV VLPs hemagglutinated only chimpanzee and human RBCs. The rNV VLPs hemagglutinated all human type O (11 of 11), A (9 of 9), and AB (4 of 4) RBCs; however, few human type B RBC samples (4 of 14) were hemagglutinated. HA with periodate- and neuraminidase-treated RBCs indicated that rNV VLP binding was carbohydrate dependent and did not require sialic acid. The rNV VLPs did not hemagglutinate Bombay RBCs (zero of seven) that lack H type 2 antigen, and an anti-H type 2 antibody inhibited rNV VLP HA of human type O RBCs. These data indicated that the H type 2 antigen functions as the rNV VLP HA receptor on human type O RBCs. The rNV VLP HA was also inhibited by rNV VLP-specific monoclonal antibody 8812, an antibody that inhibits VLP binding to Caco-2 cells. Convalescent-phase sera from NV-infected individuals showed increased rNV VLP HA inhibition titers compared to prechallenge sera. In carbohydrate binding assays, the rNV VLPs bound to synthetic Lewis d (Le(d)), Le(b), H type 2, and Le(y) antigens, and these antigens also inhibited rNV VLP HA of human type O RBCs. Overall, our results indicate that carbohydrate antigens in the gut are a previously unrecognized factor in NV pathogenesis.

Usage of Aplysia lectin interactions with T antigen and poly-N-acetyllactosamine for screening of E. coli strains which bear glycoforms cross-reacting with cancer-associated antigens

Aplysia gonad lectin (AGL), which strongly agglutinates cancer cells, was found, in the present study, to bind to erythrocyte T antigen, in addition to its affinity to Ii system antigens. These antigens were reported to be overexpressed and to contribute to tumor progression and invasion. In healthy human sera, there are antibodies against them, stimulated by the normal intestinal microflora, which bear similar glycoforms. Since the levels of these antibodies were reported to be lower in most cancer patients' sera, we have examined the applicability of AGL to isolation of enteric commensal Escherichia coli strains which bear glycoforms cross-reacting with the cancer-associated antigens. Among 30 E. coli isolates examined, two were agglutinated by AGL. One of them was also agglutinated by certain related galactophilic lectins, which bind to the T and Tn antigens. The agglutination of the two bacteria by healthy human sera, as a group, was stronger than that displayed by the cancer patients' sera. These results indicate that AGL might be useful for identification of the desired bacteria, which could potentially serve for cancer diagnosis and therapy.

Binding Properties and Applications of Aplysia Gonad Lectin

Adult Aplysia gonad contains high levels of a galactophilic lectin (MW around 65 kDa; composed of 2 subunits of apparent single species). It binds galactose and various alpha/beta-galactosides (but not N-acetylgalactosamine), in addition to an outstanding high affinity for galacturonic acid. This lectin is relatively resistant to heating up to 70 degrees C and to alkaline pH, but sensitive to proteolysis and low pH. It resembles galectins in binding to poly LacNAc (preferentially branched) complexes at low temperatures (0 degrees-4 degrees C) more avidly than at room temperature or at 37 degrees C, but differs from them in being Ca(2+)-dependent. It agglutinates papain/sialidase-treated erythrocytes more strongly than untreated cells and stimulates mitosis in peripheral human lymphocytes (inducing IL-2 formation). This lectin also enhances neurite outgrowth and increases their viability, while suppressing cell tumorigenicity. It is useful for histochemical/ cytochemical studies of galacturonic acid in plant tissues and fungi and for the study of cell surface composition of various prokaryotic (including halophilic Archaea) and eukaryotic cells and for their typing. It is useful as a reagent for I-antigen detection in adult human erythrocytes (anti-I), exhibiting strongest agglutination of O(h) Bombay-type erythrocytes and also exhibits sensitivity to the T antigen. It binds galactosylated molecules in human body fluids (shown by hemagglutination--inhibition tests), including saliva, seminal fluid and milk (detecting individual divergence) and in fowl egg albumens (exhibiting highest affinity for that of pigeon). Therefore, it might be valuable as a probe and fishhook for fishing compounds exhibiting anti-bacterial/neoplastic cell adhesion activities.