Cloning, expression in Escherichia coli and characterization of the recombinant Neu5Acalpha2,6Galbeta1,4GlcNAc-specific high-affinity lectin and its mutants from the mushroom Polyporus squamosus

A tailored lectin microarray for rapid glycan profiling of therapeutic monoclonal antibodies

Glycosylation plays a crucial role in determining the quality and efficacy of therapeutic antibodies. This necessitates a thorough analysis and monitoring process to ensure consistent product quality during manufacturing. In this study, we introduce a custom-designed lectin microarray featuring nine distinct lectins: rPhoSL, rOTH3, RCA120, rMan2, MAL_I, rPSL1a, PHAE, rMOA, and PHAL. These lectins have been specifically tailored to selectively bind to common N-glycan epitopes found in therapeutic IgG antibodies. By utilizing intact glycoprotein samples, our nine-lectin microarray provides a high-throughput platform for rapid glycan profiling, enabling comparative analysis of glycosylation patterns. Our results demonstrate the practical utility of this microarray in assessing glycosylation across various manufacturing batches or between biosimilar and innovator products. This capacity empowers informed decision-making in the development and production of therapeutic antibodies.

Development and applications of sialoglycan-recognizing probes (SGRPs) with defined specificities: exploring the dynamic mammalian sialoglycome

Glycans that are abundantly displayed on vertebrate cell surface and secreted molecules are often capped with terminal sialic acids (Sias). These diverse 9-carbon-backbone monosaccharides are involved in numerous intrinsic biological processes. They also interact with commensals and pathogens, while undergoing dynamic changes in time and space, often influenced by environmental conditions. However, most of this sialoglycan complexity and variation remains poorly characterized by conventional techniques, which often tend to destroy or overlook crucial aspects of Sia diversity and/or fail to elucidate native structures in biological systems, i.e. in the intact sialome. To date, in situ detection and analysis of sialoglycans has largely relied on the use of plant lectins, sialidases, or antibodies, whose preferences (with certain exceptions) are limited and/or uncertain. We took advantage of naturally evolved microbial molecules (bacterial adhesins, toxin subunits, and viral hemagglutinin-esterases) that recognize sialoglycans with defined specificity to delineate 9 classes of sialoglycan recognizing probes (SGRPs: SGRP1-SGRP9) that can be used to explore mammalian sialome changes in a simple and systematic manner, using techniques common in most laboratories. SGRP candidates with specificity defined by sialoglycan microarray studies were engineered as tagged probes, each with a corresponding nonbinding mutant probe as a simple and reliable negative control. The optimized panel of SGRPs can be used in methods commonly available in most bioscience labs, such as ELISA, western blot, flow cytometry, and histochemistry. To demonstrate the utility of this approach, we provide examples of sialoglycome differences in tissues from C57BL/6 wild-type mice and human-like Cmah-/- mice.

Integrated analysis of glycan and RNA in single cells

Single-cell sequencing has emerged as an indispensable technology to dissect cellular heterogeneity but never been applied to the simultaneous analysis of glycan and RNA. Using oligonucleotide-labeled lectins, we first established lectin-based glycan profiling of single cells by sequencing (scGlycan-seq). We then combined the scGlycan-seq with single-cell transcriptome profiling for joint analysis of glycan and RNA in single cells (scGR-seq). Using scGR-seq, we analyzed the two modalities in human induced pluripotent stem cells (hiPSCs) before and after differentiation into neural progenitor cells at the single-cell resolution. The combination of RNA and glycan separated the two cell types clearer than either one of them. Furthermore, integrative analysis of glycan and RNA modalities in single cells found known and unknown lectins that were specific to hiPSCs and coordinated with neural differentiation. Taken together, we demonstrate that scGR-seq can reveal the cellular heterogeneity and biological roles of glycans across multicellular systems.

An efficient heterologous Escherichia coli-based expression system for lectin production from Pleurocybella porrigens

In this study, we report a more efficient heterologous expression of lectin from Pleurocybella porrigens (PPL) using an Escherichia coli-based expression system. The yield (9.3 mg/L culture broth) of recombinant PPL (rPPL) using this expression system was increased approximately 9-fold compared to our previous study. The rPPL obtained in this study exhibited the same biochemical properties as the native PPL.

Recent approaches for directly profiling cell surface sialoform

Sialic acids (SAs) are nine-carbon monosaccharides existing at the terminal location of glycan structures on the cell surface and secreted glycoconjugates. The expression levels and linkages of SAs on cells and tissues, collectively known as sialoform, present the hallmark of the cells and tissues of different systems and conditions. Accordingly, detecting or profiling cell surface sialoforms is very critical for understanding the function of cell surface glycans and glycoconjugates and even the molecular mechanisms of their underlying biological processes. Further, it may provide therapeutic and diagnostic applications for different diseases. In the past decades, several kinds of SA-specific binding molecules have been developed for detecting and profiling specific sialoforms of cells and tissues; the experimental materials have expanded from frozen tissue to living cells; and the analytical technologies have advanced from histochemistry to fluorescent imaging, flow cytometry and microarrays. This review summarizes the recent bioaffinity approaches for directly detecting and profiling specific SAs or sialylglycans, and their modifications of different cells and tissues.

Neutrophil-released enzymes can influence composition of circulating immune complexes in multiple sclerosis

During NET formation, the content of neutrophils granules is released into the intercellular milieu. Consisting of many proteases and ROS species, formed NETs were shown to degrade cytokines (Schauer, Nat Med, 2014); while the content of neutrophil's azurophilic granules proved to contain glycosidases, secreted upon activation (Thaysen-Andersen, JBC, 2015), and formation of autoantibodies to neutrophil beta-glucoronidase was connected with the level of anti-MPO antibodies (Ab) (Martensson, Autoimmunity, 1992). Taking into account these facts, we aimed to investigate the possibility of NET-related changes in glycan composition on circulating IgG molecules and IgG-IgM immune complexes in multiple sclerosis (MS). This autoimmune disorder still has no reliable detection markers or established ways of treatment, besides widely accepted interferon therapy, making it a particularly interesting clinical condition. By applying capture lectin-ELISA, we analysed binding of α2,6 sialyl-specific lectins SNA, PSqL, and core α1,6-fucose specific lectin AAL to circulating IgG and related complexes in five groups of MS patients: untreated (17 persons); undergoing therapy with interferon (IFN) β-1 b (15 persons), corticosteroids (methylprednisolone) (12 persons) and anti-B-cell monoclonal Ab (12 persons: Ocrelizumab, 6 persons and alemtuzumab, 6 persons). A group of 23 healthy donors served as control. Significant increase in neutrophil elastase activity, observed in the group of patients under corticosteroid treatment was also accompanied by sialyl-specific PSqL and SNA lectin binding to captured IgG molecules. Subsequent analysis demonstrated that sialic acid residues were exposed on free IgG and on circulating IgG-IgM immune complexes. Increased lectin binding was not observed for anti-myelin basic protein (one of the major autoAb in MS) Ab compared to total serum Ab. IFN therapy was accompanied by low neutrophil elastase activity and low amount of circulating immune complexes. Incubation of in vitro generated NETs with human serum revealed the digestion of high-molecular weight immune complexes with subsequent exposure of hidden glycoepitops. Obtained data indicate the potential of neutrophil-derived proteases to modify (partially degrade) circulating immune complexes leading to exposure of internal glycoepitops.

Structure and function analysis of Polygonatum cyrtonema lectin by site-directed mutagenesis

The crystal structure of mature Polygonatum cyrtonema lectin (PCL) showed three similar carbohydrate-binding sites (CBS I, CBS II, and CBS III). The Gln58 and Asp60 residues of CBS II are substituted with His58 and Asn60. To establish the relationship between the key amino acid residues and structure or activity of PCL, we constructed four recombinant mutants in CBS I, CBS II, and CBS III. The experimental results indicate that CBS I, CBS III and the disulfide bond play vital roles in the binding with mannose. Furthermore, molecular dynamics simulations and binding free energy calculation illustrate that CBS I has a direct and strong relationship with the activity of PCL. CBS II does not play a critical role in the model for mannose binding by PCL. Although CBS III does not enhance the activity, it helps to maintain the activity and 3D structure. These results suggest that the carbohydrate-binding site of PCL may be in a hydrophilic environment, and Asn and Tyr are the key amino acids involved in its binding with sugar, but Gln and Asp are not necessary to maintain its activity.

Recombinant protein expression of Moringa oleifera lectin in methylotrophic yeast as active coagulant for sustainable high turbid water treatment

The natural coagulant Moringa oleifera lectin (MoL) as cationic protein is a promising candidate in coagulation process of water treatment plant. Introducing the gene encoding MoL into a host, Pichia pastoris, to secrete soluble recombinant protein is assessed in this study. Initial screening using PCR confirmed the insertion of MoL gene, and SDS-PAGE analysis detected the MoL protein at 8 kDa. Cultured optimization showed the highest MoL protein at 520 mg/L was observed at 28 °C for 144 h of culturing by induction in 1% methanol. Approximately, 0.40 mg/mL of recombinant MoL protein showed 95 ± 2% turbidity removal of 1% kaolin suspension. In 0.1% kaolin suspension, the concentration of MoL at 10 μg/mL exhibits the highest turbidity reduction at 68 ± 1%. Thus, recombinant MoL protein from P. pastoris is an effective coagulant for water treatment.

Characterization of a high-affinity sialic acid-specific CBM40 from Clostridium perfringens and engineering of a divalent form

CBMs (carbohydrate-binding modules) are a class of polypeptides usually associated with carbohydrate-active enzymatic sites. We have characterized a new member of the CBM40 family, coded from a section of the gene NanI from Clostridium perfringens. Glycan arrays revealed its preference towards α(2,3)-linked sialosides, which was confirmed and quantified by calorimetric studies. The CBM40 binds to α(2,3)-sialyl-lactose with a Kd of ∼30 μM, the highest affinity value for this class of proteins. Inspired by lectins' structure and their arrangement as multimeric proteins, we have engineered a dimeric form of the CBM, and using SPR (surface plasmon resonance) we have observed 6–11-fold binding increases due to the avidity affect. The structures of the CBM, resolved by X-ray crystallography, in complex with α(2,3)- or α(2,6)-sialyl-lactose explain its binding specificity and unusually strong binding.

Comprehensive list of lectins: origins, natures, and carbohydrate specificities

More than 100 years have passed since the first lectin ricin was discovered. Since then, a wide variety of lectins (lect means "select" in Latin) have been isolated from plants, animals, fungi, bacteria, as well as viruses, and their structures and properties have been characterized. At present, as many as 48 protein scaffolds have been identified as functional lectins from the viewpoint of three-dimensional structures as described in this chapter. In this chapter, representative 53 lectins are selected, and their major properties that include hemagglutinating activity, mitogen activity, blood group specificity, molecular weight, metal requirement, and sugar specificities are summarized as a comprehensive table. The list will provide a practically useful, comprehensive list for not only experienced lectin users but also many other non-expert researchers, who are not familiar to lectins and, therefore, have no access to advanced lectin biotechnologies described in other chapters.

Plasticity of the β-trefoil protein fold in the recognition and control of invertebrate predators and parasites by a fungal defence system

Discrimination between self and non-self is a prerequisite for any defence mechanism; in innate defence, this discrimination is often mediated by lectins recognizing non-self carbohydrate structures and so relies on an arsenal of host lectins with different specificities towards target organism carbohydrate structures. Recently, cytoplasmic lectins isolated from fungal fruiting bodies have been shown to play a role in the defence of multicellular fungi against predators and parasites. Here, we present a novel fruiting body lectin, CCL2, from the ink cap mushroom Coprinopsis cinerea. We demonstrate the toxicity of the lectin towards Caenorhabditis elegans and Drosophila melanogaster and present its NMR solution structure in complex with the trisaccharide, GlcNAcβ1,4[Fucα1,3]GlcNAc, to which it binds with high specificity and affinity in vitro. The structure reveals that the monomeric CCL2 adopts a β-trefoil fold and recognizes the trisaccharide by a single, topologically novel carbohydrate-binding site. Site-directed mutagenesis of CCL2 and identification of C. elegans mutants resistant to this lectin show that its nematotoxicity is mediated by binding to α1,3-fucosylated N-glycan core structures of nematode glycoproteins; feeding with fluorescently labeled CCL2 demonstrates that these target glycoproteins localize to the C. elegans intestine. Since the identified glycoepitope is characteristic for invertebrates but absent from fungi, our data show that the defence function of fruiting body lectins is based on the specific recognition of non-self carbohydrate structures. The trisaccharide specifically recognized by CCL2 is a key carbohydrate determinant of pollen and insect venom allergens implying this particular glycoepitope is targeted by both fungal defence and mammalian immune systems. In summary, our results demonstrate how the plasticity of a common protein fold can contribute to the recognition and control of antagonists by an innate defence mechanism, whereby the monovalency of the lectin for its ligand implies a novel mechanism of lectin-mediated toxicity.

Characterization of a new α-galactosyl-binding lectin from the mushroom Clavaria purpurea

A galactose specific lectin (CpL) was purified from the Clavaria purpurea mushroom by affinity chromatography. CpL agglutinated only trypsin-treated rabbit erythrocytes. On enzyme linked lectin sorbent assay (ELLSA), the lectin bound with thyroglobulin and asialo bovine submaxillary mucin (BSM). The fine sugar binding specificity of CpL was elucidated using inhibition of hemagglutination and sugar immobilized gold nano-particles (SGNP). The results indicated a preference of CpL towards α-galactosyl sugar chains. Among several monosaccharides and disaccharides assayed for dissociation effect on the SGNP-CpL complex, Galα1-3Gal and raffinose were the best inhibitors. The partial amino acid sequence showed two QXW motifs in CpL and similarity towards members of the ricin B superfamily.

Nematotoxicity of Marasmius oreades agglutinin (MOA) depends on glycolipid binding and cysteine protease activity

Fruiting body lectins have been proposed to act as effector proteins in the defense of fungi against parasites and predators. The Marasmius oreades agglutinin (MOA) is a Galα1,3Gal/GalNAc-specific lectin from the fairy ring mushroom that consists of an N-terminal ricin B-type lectin domain and a C-terminal dimerization domain. The latter domain shows structural similarity to catalytically active proteins, suggesting that, in addition to its carbohydrate-binding activity, MOA has an enzymatic function. Here, we demonstrate toxicity of MOA toward the model nematode Caenorhabditis elegans. This toxicity depends on binding of MOA to glycosphingolipids of the worm via its lectin domain. We show further that MOA has cysteine protease activity and demonstrate a critical role of this catalytic function in MOA-mediated nematotoxicity. The proteolytic activity of MOA was dependent on high Ca(2+) concentrations and favored by slightly alkaline pH, suggesting that these conditions trigger activation of the toxin at the target location. Our results suggest that MOA is a fungal toxin with intriguing similarities to bacterial binary toxins and has a protective function against fungivorous soil nematodes.

Molecular diversity of the two sugar-binding sites of the β-trefoil lectin HA33/C (HA1) from Clostridium botulinum type C neurotoxin

A critical role in internalizing the Clostridium botulinum neurotoxin into gastrointestinal cells is played by nontoxic components complexed with the toxin. One of the components, a β-trefoil lectin has been known as HA33 or HA1. The HA33 from C. botulinum type A (HA33/A) has been predicted to have a single sugar-binding site, while type C HA33 (HA33/C) has two sites. Here we constructed HA33/C mutants and evaluated the binding capacities of the individual sites through mucin-assay and isothermal titration calorimetry. The mutant W176A (site I knockout) had a K(d) value of 31.5mM for galactose (Gal) and 61.3mM for N-acetylgalactosamine (GalNAc), while the K(d) value for N-acetylneuraminic acid (Neu5Ac) was too high to be determined. In contrast, the double mutant N278A/Q279A (site II knockout) had a K(d) value of 11.8mM for Neu5Ac. We also determined the crystal structures of wild-type and the F179I mutant in complex with GalNAc at site II. The results suggest that site I of HA33/C is quite unique in that it mainly recognizes Neu5Ac, and site II seems less important for the lectin specificity. The architectures and the properties of the sugar-binding sites of HA33/C and HA33/A were shown to be drastically different.

Marasmius oreades agglutinin (MOA) is a chimerolectin with proteolytic activity

The Marasmius oreades mushroom lectin (MOA) is well known for its exquisite binding specificity for blood group B antigens. In addition to its N-terminal carbohydrate-binding domain, MOA possesses a C-terminal domain with unknown function, which structurally resembles hydrolytic enzymes. Here we show that MOA indeed has catalytic activity. It is a calcium-dependent cysteine protease resembling papain-like cysteine proteases, with Cys215 being the catalytic nucleophile. The possible importance of MOA's proteolytic activity for mushroom defense against pathogens is discussed.

Structure and binding analysis of Polyporus squamosus lectin in complex with the Neu5Ac{alpha}2-6Gal{beta}1-4GlcNAc human-type influenza receptor

Glycan chains that terminate in sialic acid (Neu5Ac) are frequently the receptors targeted by pathogens for initial adhesion. Carbohydrate-binding proteins (lectins) with specificity for Neu5Ac are particularly useful in the detection and isolation of sialylated glycoconjugates, such as those associated with pathogen adhesion as well as those characteristic of several diseases including cancer. Structural studies of lectins are essential in order to understand the origin of their specificity, which is particularly important when employing such reagents as diagnostic tools. Here, we report a crystallographic and molecular dynamics (MD) analysis of a lectin from Polyporus squamosus (PSL) that is specific for glycans terminating with the sequence Neu5Acα2-6Galβ. Because of its importance as a histological reagent, the PSL structure was solved (to 1.7 Å) in complex with a trisaccharide, whose sequence (Neu5Acα2-6Galβ1-4GlcNAc) is exploited by influenza A hemagglutinin for viral adhesion to human tissue. The structural data illuminate the origin of the high specificity of PSL for the Neu5Acα2-6Gal sequence. Theoretical binding free energies derived from the MD data confirm the key interactions identified crystallographically and provide additional insight into the relative contributions from each amino acid, as well as estimates of the importance of entropic and enthalpic contributions to binding.

Lectins: production and practical applications

Lectins are proteins found in a diversity of organisms. They possess the ability to agglutinate erythrocytes with known carbohydrate specificity since they have at least one non-catalytic domain that binds reversibly to specific monosaccharides or oligosaccharides. This articles aims to review the production and practical applications of lectins. Lectins are isolated from their natural sources by chromatographic procedures or produced by recombinant DNA technology. The yields of animal lectins are usually low compared with the yields of plant lectins such as legume lectins. Lectins manifest a diversity of activities including antitumor, immunomodulatory, antifungal, HIV-1 reverse transcriptase inhibitory, and anti-insect activities, which may find practical applications. A small number of lectins demonstrate antibacterial and anti-nematode activities.

Mushroom lectins: current status and future perspectives

Lectins are nonimmune proteins or glycoproteins that bind specifically to cell surface carbohydrates, culminating in cell agglutination. These are known to play key roles in host defense system and also in metastasis. Many new sources have been explored for the occurrence of lectins during the last few years. Numerous novel lectins with unique specificities and exploitable properties have been discovered. Mushrooms have attracted a number of researchers in food and pharmaceuticals. Many species have long been used in traditional Chinese medicines or functional foods in Japan and other Asian countries. A number of bioactive constituents have been isolated from mushrooms including polysaccharides, polysaccharopeptides, polysaccharide-protein complexes, proteases, ribonucleases, ribosome inactivating proteins, antifungal proteins, immunomodulatory proteins, enzymes, lectins, etc. Mushroom lectins are endowed with mitogenic, antiproliferative, antitumor, antiviral, and immune stimulating potential. In this review, an attempt has been made to collate the information on mushroom lectins, their blood group and sugar specificities, with an emphasis on their biomedical potential and future perspectives.

Structural characterization of a lectin from the mushroom Marasmius oreades in complex with the blood group B trisaccharide and calcium

MOA (Marasmius oreades agglutinin), a lectin isolated from fruiting bodies of the mushroom M. oreades, specifically binds nonreducing terminal Galalpha(1,3)Gal carbohydrates, such as that which occurs in the xenotransplantation epitope Galalpha(1,3)Galbeta(1,4)GlcNAc and the branched blood group B determinant Galalpha(1,3)[Fucalpha(1,2)]Gal. Here, we present the crystal structure of MOA in complex with the blood group B trisaccharide solved at 1.8 A resolution. To our knowledge, this is the first blood-group-B-specific structure reported in complex with a blood group B determinant. The carbohydrate ligand binds to all three binding sites of the N-terminal beta-trefoil domain. Also, in this work, Ca(2+) was included in the crystals, and binding of Ca(2+) to the MOA homodimer altered the conformation of the C-terminal domain by opening up the cleft containing a putative catalytic site.

Purification, characterization and cloning of a ricin B-like lectin from mushroom Clitocybe nebularis with antiproliferative activity against human leukemic T cells

BACKGROUND

Lectins are a diverse group of carbohydrate-binding proteins exhibiting numerous biological activities and functions.

METHODS

Two-step serial carbohydrate affinity chromatography was used to isolate a lectin from the edible mushroom clouded agaric (Clitocybe nebularis). It was characterized biochemically, its gene and cDNA cloned and the deduced amino acid sequence analyzed. Its activity was tested by hemagglutination assay and carbohydrate-binding specificity determined by glycan microarray analysis. Its effect on proliferation of several human cell lines was determined by MTS assay.

RESULTS

A homodimeric lectin with 15.9-kDa subunits agglutinates human group A, followed by B, O, and bovine erythrocytes. Hemagglutination was inhibited by glycoprotein asialofetuin and lactose. Glycan microarray analysis revealed that the lectin recognizes human blood group A determinant GalNAcalpha1-3(Fucalpha1-2)Galbeta-containing carbohydrates, and GalNAcbeta1-4GlcNAc (N,N'-diacetyllactosediamine). The lectin exerts antiproliferative activity specific to human leukemic T cells.

CONCLUSIONS

The protein belongs to the ricin B-like lectin superfamily, and has been designated as C. nebularis lectin (CNL). Its antiproliferative effect appears to be elicited by binding to carbohydrate receptors on human leukemic T cells.

GENERAL SIGNIFICANCE

CNL is one of the few mushroom ricin B-like lectins that have been identified and the only one so far shown to possess immunomodulatory properties.

Detection of a high affinity binding site in recombinant Aleuria aurantia lectin

Lectins are carbohydrate binding proteins that are involved in many recognition events at molecular and cellular levels. Lectin-oligosaccharide interactions are generally considered to be of weak affinity, however some mushroom lectins have unusually high binding affinity towards oligosaccharides with K (d) values in the micromolar range. This would make mushroom lectins ideal candidates to study protein-carbohydrate interactions. In the present study we investigated the properties of a recombinant form of the mushroom lectin Aleuria aurantia (AAL). AAL is a fucose-binding lectin composed of two identical 312-amino acid subunits. Each subunit contains five binding sites for fucose. We found that one of the binding sites in rAAL had unusually high affinities towards fucose and fucose-containing oligosaccharides with K (d) values in the nanomolar range. This site could bind to oligosaccharides with fucose linked alpha1-2, alpha1-3 or alpha1-4, but in contrast to the other binding sites in AAL it could not bind oligosaccharides with alpha1-6 linked fucose. This binding site is not detected in native AAL (nAAL) one possible explanation may be that this site is blocked with free fucose in nAAL. Recombinant AAL was produced in E. coli as a His-tagged protein, and purified in a one-step procedure. The resulting protein was analyzed by electrophoresis, enzyme-linked lectin assay and circular dichroism spectroscopy, and compared to nAAL. Binding properties were measured using tryptophan fluorescence and surface plasmon resonance. Removal of the His-tag did not alter the binding properties of recombinant AAL in the enzyme-linked lectin assay. Our study forms a basis for understanding the AAL-oligosaccharide interaction and for using molecular techniques to design lectins with novel specificities and high binding affinities towards oligosaccharides.

Frontal affinity chromatography: sugar-protein interactions

Frontal affinity chromatography using fluorescence detection (FAC-FD) is a versatile technique for the precise determination of dissociation constants (Kd) between glycan-binding proteins (lectins) and fluorescent-labeled glycans. A series of glycan-containing solutions is applied to a lectin-immobilized column, and the elution profile of each glycan (termed the 'elution front', V) is compared with that (V0) for an appropriate control. Here we describe our standard protocol using an automated FAC system (FAC-1), consisting of two isocratic pumps, an autosampler, a column oven and two miniature columns connected to a fluorescence detector. Analysis time for 100 sugar-protein interactions is approximately 10 h, using as little as 2.5 pmol of pyridylaminated (PA) oligosaccharide per analysis. Using FAC-FD, we have so far obtained quantitative interaction data of >100 lectins for >100 PA oligosaccharides.

A mushroom lectin from ascomycete Cordyceps militaris

A mushroom lectin has been purified from ascomycete Cordyceps militaris, which is one of the most popular mushrooms in eastern Asia used as a nutraceutical and in traditional Chinese medicine. This lectin, designated CML, exhibited hemagglutination activity in mouse and rat erythrocytes, but not in human ABO erythrocytes. SDS-PAGE of CML revealed a single band with a molecular mass of 31.0 kDa under both nonreducing and reducing conditions that was stained by silver nitrate, and a 31.4 kDa peak in a Superdex-200 HR gel-filtration column. The hemagglutination activity was inhibited by sialoglycoproteins, but not in by mono- or disaccharides, asialoglycoproteins, or de-O-acetylated glycoprotein. The activity was maximal at pH 6.0-9.1 and at temperatures below 50 degrees C. Circular dichroism spectrum analysis revealed that CML comprises 27% alpha-helix, 12% beta-sheets, 29% beta-turns, and 32% random coils. Its binding specificity and secondary structure are similar to those of a fungal lectin from Arthrobotrys oligospora. However, the N-terminal amino acid sequence of CML differs greatly from those of other lectins. CML exhibits mitogenic activity against mouse splenocytes.

The Sclerotinia sclerotiorum agglutinin represents a novel family of fungal lectins remotely related to the Clostridium botulinum non-toxin haemagglutinin HA33/A

Previous studies indicated that sclerotes of the phytopathogenic Ascomycete Sclerotinia sclerotiorum contain a lectin that based on its molecular structure, specificity and N-terminal amino acid sequence could not be classified yet into any lectin family. Using a combination of molecular cloning, frontal affinity chromatography and molecular modelling the identity of the S. sclerotiorum agglutinin (SSA) was analyzed. Molecular cloning demonstrated that SSA shares no sequence similarity with any known fungal lectin or protein. The lectin is synthesized as a 153 amino acid polypeptide without signal peptide and undergoes apart from the removal of the N-terminal methionine no further processing. Frontal affinity chromatography revealed that the binding site of SSA primarily accommodates a non-reducing terminal GalNAc with a preference for the alpha- over the beta-anomer. SSA also strongly interacts with both glycolipid type glycans with terminal non-reducing Gal or GalNAc and galactosylated N-glycans. SSA shares a residual sequence similarity with part of the non-toxin haemagglutinin HA33/A from Clostridium botulinum. Molecular modeling using the three-dimensional structure of HA33/A as a template indicated that SSA can fold into a similar beta-trefoil domain. Though these results should be interpreted with care it is tempting to speculate that the Sclerotiniaceae lectins thus appear to be structurally related to the ricin-B superfamily. All evidence suggests that SSA represents a novel family of fungal lectins with a unique sequence and sugar-binding properties. Taking into account that orthologues of SSA are fairly common within the family Sclerotiniaceae but could not be identified in any other fungal species one can reasonably conclude that SSA-type lectins are confined to a small taxonomic group of the Ascomycota.

Essential regions for antiviral activities of actinohivin, a sugar-binding anti-human immunodeficiency virus protein from an actinomycete

Actinohivin (AH) is a potent anti-human immunodeficiency virus (HIV) protein that consists of highly conserved three-tandem repeats (segments 1, 2, and 3). The molecular target of AH in its anti-HIV activity is high-mannose-type saccharide chains of HIV gp120. This article deals with sequence requirements for the anti-HIV activity of AH. The deleted or substituted DNAs encoding AH or His-AH were prepared using mutagenic oligonucleotide primers in PCR. The mutant constructs were expressed in Escherichia coli, and the activities of the recombinant protein products were examined by a syncytium-formation assay system that mimics anti-HIV activity. The single segment mutant His-AHs showed no anti-syncytium-formation activity, but the mutant His-AHs, which consists of 2 or 3 segments, retained reduced activities. His-AH(6-114) dramatically reduced the anti-syncytium-formation activity to that of His-AH(36-114) or His-AH(I5A). Furthermore, His-AH(Q33A), His-AH(Q71A), and His-AH(Q109A) in which glutamine residues were substituted into alanine showed reduced activities of 1/20, 1/10, and 1/30, respectively, in anti-syncytium formation compared with His-AH. These results indicate that three segments of AH are necessary for potent anti-syncytium-formation activity-that is, for potent anti-HIV activity and the cooperated involvement of each segment of AH increased the AH-gp120 interaction.