A novel mannose-specific and sugar specifically aggregatable lectin from the bark of the Japanese pagoda tree (Sophora japonica)

Secreted filarial nematode galectins modulate host immune cells

Lymphatic filariasis (LF) is a mosquito-borne disease caused by filarial nematodes including Brugia malayi. Over 860 million people worldwide are infected or at risk of infection in 72 endemic countries. The absence of a protective vaccine means that current control strategies rely on mass drug administration programs that utilize inadequate drugs that cannot effectively kill adult parasites, thus established infections are incurable. Progress to address deficiencies in the approach to LF control is hindered by a poor mechanistic understanding of host-parasite interactions, including mechanisms of host immunomodulation by the parasite, a critical adaptation for establishing and maintaining infections. The canonical type 2 host response to helminth infection characterized by anti-inflammatory and regulatory immune phenotypes is modified by filarial nematodes during chronic LF. Current efforts at identifying parasite-derived factors driving this modification focus on parasite excretory-secretory products (ESP), including extracellular vesicles (EVs). We have previously profiled the cargo of B. malayi EVs and identified B. malayi galectin-1 and galectin-2 as among the most abundant EV proteins. In this study we further investigated the function of these proteins. Sequence analysis of the parasite galectins revealed highest homology to mammalian galectin-9 and functional characterization identified similar substrate affinities consistent with this designation. Immunological assays showed that Bma-LEC-2 is a bioactive protein that can polarize macrophages to an alternatively activated phenotype and selectively induce apoptosis in Th1 cells. Our data shows that an abundantly secreted parasite galectin is immunomodulatory and induces phenotypes consistent with the modified type 2 response characteristic of chronic LF infection.

Unassembled cell wall proteins form aggregates in the extracellular space of Chlamydomonas reinhardtii strain UVM4

Abstract

The green microalga Chlamydomonas reinhardtii is emerging as a promising cell biofactory for secreted recombinant protein (RP) production. In recent years, the generation of the broadly used cell wall–deficient mutant strain UVM4 has allowed for a drastic increase in secreted RP yields. However, purification of secreted RPs from the extracellular space of C. reinhardtii strain UVM4 is challenging. Previous studies suggest that secreted RPs are trapped in a matrix of cell wall protein aggregates populating the secretome of strain UVM4, making it difficult to isolate and purify the RPs. To better understand the nature and behaviour of these extracellular protein aggregates, we analysed and compared the extracellular proteome of the strain UVM4 to its cell-walled ancestor, C. reinhardtii strain 137c. When grown under the same conditions, strain UVM4 produced a unique extracellular proteomic profile, including a higher abundance of secreted cell wall glycoproteins. Further characterization of high molecular weight extracellular protein aggregates in strain UVM4 revealed that they are largely comprised of pherophorins, a specific class of cell wall glycoproteins. Our results offer important new insights into the extracellular space of strain UVM4, including strain-specific secreted cell wall proteins and the composition of the aggregates possibly related to impaired RP purification. The discovery of pherophorins as a major component of extracellular protein aggregates will inform future strategies to remove or prevent aggregate formation, enhance purification of secreted RPs, and improve yields of recombinant biopharmaceuticals in this emerging cell biofactory.

Key points

• Extracellular protein aggregates hinder purification of recombinant proteins in C. reinhardtii

• Unassembled cell wall pherophorins are major components of extracellular protein aggregates

• Known aggregate composition informs future strategies for recombinant protein purification

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11960-9.

A nontoxic polypeptide oligomer with a fungicide potency under agricultural conditions which is equal or greater than that of their chemical counterparts

There are literally hundreds of polypeptides described in the literature which exhibit fungicide activity. Tens of them have had attempted protection by patent applications but none, as far as we are aware, have found application under real agricultural conditions. The reasons behind may be multiple where the sensitivity to the Sun UV radiation can come in first place. Here we describe a multifunctional glyco-oligomer with 210 kDa which is mainly composed by a 20 kDa polypeptide termed Blad that has been previously shown to be a stable intermediary product of β-conglutin catabolism. This oligomer accumulates exclusively in the cotyledons of Lupinus species, between days 4 and 12 after the onset of germination. Blad-oligomer reveals a plethora of biochemical properties, like lectin and catalytic activities, which are not unusual per si, but are remarkable when found to coexist in the same protein molecule. With this vast range of chemical characteristics, antifungal activity arises almost as a natural consequence. The biological significance and potential technological applications of Blad-oligomer as a plant fungicide to agriculture, its uniqueness stems from being of polypeptidic in nature, and with efficacies which are either equal or greater than the top fungicides currently in the market are addressed.

Preparation of affinity adsorbents and purification of lectins from natural sources

Lectins are purified by affinity chromatography to take advantage of their carbohydrate-specific interactions. Highly efficient affinity adsorbents are powerful tools to obtain homogeneous lectins with distinct specificities. Here, we describe three methods to prepare affinity adsorbents by immobilizing carbohydrates or glycoconjugates on agarose gel beads. Because the ligands are immobilized via a stable and nonionic linkage under mild conditions, the adsorbents possess high binding capacity for lectins with low nonspecific adsorption and can withstand repeated use. The procedures require neither specialized techniques and apparatus nor highly toxic compounds. Using these adsorbents, many plant and animal lectins can be purified in a few steps.

Solid-phase assay of lectin activity using HRP-conjugated glycoproteins

Various enzyme-conjugated probes have been widely used for detection of specific interactions between biomolecules. In the case of glycan-protein interaction, horseradish peroxidase (HRP)-conjugated glycoproteins (HRP-GPs) are useful for the detection of carbohydrate-binding activity of plant and animal lectins. In this chapter, a typical solid-phase assay of the carbohydrate-binding activity of Sophora japonica agglutinin I, a Gal/GalNAc-specific lectin, using HRP-conjugated asialofetuin is described. HRP-GPs are versatile tools for probing lectin activities in crude extracts, screening many samples at one time, and applicable not only for solid-phase binding assays but also samples which are dot- or Western-blotted onto the membrane.

Hemagglutination (inhibition) assay

The hemagglutination assay is a simple and easy method to obtain semi-quantitative data on the sugar binding and specificity of a lectin. An active lectin agglutinates erythrocytes by recognizing a carbohydrate on the cell surface and forming a cross-linked network in suspension. By serially diluting the lectin in a 96-well microtiter plate and adding a constant quantity of erythrocytes, the lectin activity can be estimated.

Functional regulation of sugar assimilation by N-glycan-specific interaction of pancreatic α-amylase with glycoproteins of duodenal brush border membrane

Porcine pancreatic α-amylase (PPA) binds to N-linked glycans of glycoproteins (Matsushita, H., Takenaka, M., and Ogawa, H. (2002) J. Biol Chem., 277, 4680-4686). Immunostaining revealed that PPA is located at the brush-border membrane (BBM) of enterocytes in the duodenum and that the binding is inhibited by mannan but not galactan, indicating that PPA binds carbohydrate-specifically to BBM. The ligands for PPA in BBM were identified as glycoprotein N-glycans that are significantly involved in the assimilation of glucose, including sucrase-isomaltase (SI) and Na(+)/Glc cotransporter 1 (SGLT1). Binding of SI and SGLT1 in BBM to PPA was dose-dependent and inhibited by mannan. Using BBM vesicles, we found functional changes in PPA and its ligands in BBM due to the N-glycan-specific interaction. The starch-degrading activity of PPA and maltose-degrading activity of SI were enhanced to 240 and 175%, respectively, while Glc uptake by SGLT1 was markedly inhibited by PPA at high but physiologically possible concentrations, and the binding was attenuated by the addition of mannose-specific lectins, especially from Galanthus nivalis. Additionally, recombinant human pancreatic α-amylases expressed in yeast and purified by single-step affinity chromatography exhibited the same carbohydrate binding specificity as PPA in binding assays with sugar-biotinyl polymer probes. The results indicate that mammalian pancreatic α-amylases share a common carbohydrate binding activity and specifically bind to the intestinal BBM. Interaction with N-glycans in the BBM activated PPA and SI to produce much Glc on the one hand and to inhibit Glc absorption by enterocytes via SGLT1 in order to prevent a rapid increase in blood sugar on the other.

The pherophorins: common, versatile building blocks in the evolution of extracellular matrix architecture in Volvocales

Green algae of the order Volvocales provide an unrivalled opportunity for exploring the transition from unicellularity to multicellularity. They range from unicells, like Chlamydomonas, through homocytic colonial forms with increasing cooperation of individual cells, like Gonium or Pandorina, to heterocytic multicellular forms with different cell types and a complete division of labour, like Volvox. A fundamental requirement for the evolution of multicellularity is the development of a complex, multifunctional extracellular matrix (ECM). The ECM has many functions, which can change under developmental control or as a result of environmental factors. Here molecular data from 15 novel proteins are presented. These proteins have been identified in Chlamydomonas reinhardtii, Gonium pectorale, Pandorina morum and Volvox carteri, and all belong to a single protein family, the pherophorins. Pherophorin-V1 is shown to be a glycoprotein localized to the 'cellular zone' of the V. carteri ECM. Pherophorin-V1 and -V2 mRNAs are strongly induced not only by the sex inducer, which triggers sexual development at extremely low concentrations, but also by mechanical wounding. Like the extensins of higher plants, which are also developmentally controlled or sometimes inducible by wounding, the pherophorins contain a (hydroxy-)proline-rich (HR) rod-like domain and are abundant within the extracellular compartment. In contrast to most extensins, pherophorins have additional globular A and B domains on both ends of the HR domains. Therefore pherophorins most closely resemble a particular class of higher plant extensin, the solanaceous lectins (e.g. potato lectin), suggesting multivalent carbohydrate-binding functions are present within the A and B domains and are responsible for cross-linking. Our results suggest that pherophorins are used as the building blocks for the extracellular scaffold throughout the Volvocales, with the characteristic mesh sizes in different ECM structures being a result of the highly diverse extensions of the HR domains. Pherophorins have therefore been a versatile element during the evolution of ECM architecture in these green algae.

Screening for and purification of novel self-aggregatable lectins reveal a new functional lectin group in the bark of leguminous trees

A solubility-insolubility transition assay was used to screen the bark and stems of seven leguminous trees and plants for self-aggregatable lectins. Novel lectins were found in two trees, Robinia pseudoacacia and Wisteria floribunda, but not in the leguminous plants. The Robinia lectin was isolated from coexisting lectin by combined affinity chromatographies on various sugar adsorbents. The purified lectins proved to be differently glycosylated glycoproteins. One lectin exhibited the remarkable characteristics of self-aggregatable lectins: localization in the bark of legume trees, self-aggregation dissociated by N-acetylglucosamine/mannose, and coexistence with N-acetylgalactosamine/galactose-specific lectins, which are potential endogenous receptors. Self-aggregatable lectins are a functional lectin group that can link enhanced photosynthesis to dissociation of glycoproteins.

Solubility-insolubility interconversion of sophoragrin, a mannose/glucose-specific lectin in Sophora japonica (Japanese pagoda tree) bark, regulated by the sugar-specific interaction

Sophoragrin, a mannose/glucose-specific lectin in Sophora japonica (Japanese pagoda tree) bark, was the first lectin found to show self-aggregation that is dependent on the sugar concentration accompanying the interconversion between solubility and insolubility [Ueno, Ogawa, Matsumoto and Seno (1991) J. Biol. Chem. 266, 3146-3153]. The interconversion is regulated by the concentrations of Ca(2+) and specific sugars: mannose, glucose or sucrose. The specific glycotopes for sophoragrin were found in the sophoragrin subunit and an endogenous galactose-specific lectin, B-SJA-I (bark S. japonica agglutinin I), and the lectin subunit that binds to the glycotope was identified by photoaffinity glycan probes. Remarkably, the insoluble polymer of sophoragrin is dissociated by interaction with B-SJA-I into various soluble complexes. Based on these results, self-aggregation of sophoragrin was shown to be a unique homopolymerization due to the sugar-specific interaction. An immunostaining study indicated that sophoragrin localizes mainly in vacuoles of parenchymal cells coincidently with B-SJA-I. These results indicate that sophoragrin can sequester endogenous glycoprotein ligands via sugar-specific interactions, thus providing new insights into the occurrence and significance of the intravacuolar interaction shown by a legume lectin.

Self-aggregation of legume seed storage proteins inside the protein storage vacuoles is electrostatic in nature, rather than lectin-mediated

Conglutins are multisubunit, glycosylated, major storage proteins present in Lupinus seeds that self-aggregate in a calcium/magnesium-dependent manner. Two of these globulins exhibit lectin activity. The 210 kDa globulin derived from beta-conglutin that accumulates in Lupinus cotyledons during germination was used as a model protein to establish whether the self-aggregation process is electrostatic in nature or lectin-mediated. This protein binds in a very strong manner to chitin and recognizes a variety of glycoproteins including immunoglobulins G. Several compounds were tested for their inhibitory effect on the cation-dependent self-aggregation process. Sialic acid and phytin were the most effective whereas chitin and mucin were totally ineffective. The inability of the oligosaccharidic side chains of the 210 kDa protein, beta-conglutin and immunoglobulin G to interfere with the aggregation strongly supports the view that Ca/Mg are electrostatically involved in the in vitro self-aggregation of Lupinus globulins. The results suggest that calcium and magnesium ions are also electrostatically involved in vivo in the macromolecular aggregation of legume seed storage proteins, ensuring their efficient packing inside the protein storage vacuoles. This mechanism is responsible for the typical insolubility of legume globulins in water.

Comparison of methods of immobilization to enzyme-linked immunosorbent assay plates for the detection of sugar chains

The immobilization of carbohydrates for solid-phase assays, including enzyme-linked immunosorbent assay (ELISA), is difficult because they are hydrophilic. We developed four new methods for the immobilization of oligosaccharides. ELISA plates were first coated with methyl vinyl ether-maleic anhydride copolymer (MMAC) and an excess of active anhydride groups was introduced. They were subsequently reacted, in four different ways, to bind oligosaccharides. In method 1, the anhydride groups were reacted with hydrazide groups, in the presence of adipic acid dihydrazide, and then coupled to the reducing ends of sugar chains by reductive amination. In method 2, the anhydride groups were reacted with p-aminophenyl glycoside obtained by reduction with p-nitrophenyl glycoside. In method 3, the anhydride groups were reacted with 1, 6-hexamethylenediamine. Aminooxy groups were coupled to the amino groups introduced and then aminooxyacetic acid with carbodiimide and ligated to oligosaccharides by oxime formation. In method 4, stereospecifically aminated oligosaccharides reacted with the anhydride groups. We compared, in solid-phase assays systems, the ability of lectins to detect oligosaccharides immobilized with either one of these four new methods or one of the two methods previously described. Detection of sugars with lectins is useful because, in most cases, they recognize sugars stereospecifically. The immobilization method should therefore be carefully selected to avoid changing the configuration and substitution in C-1.

Interaction of a lectin from Psathyrella velutina mushroom with N-acetylneuraminic acid

A lectin from the fruiting body of Psathyrella velutina has been used as a specific probe for non-reducing terminal N-acetylglucosamine residues. We reveal in this report that P. velutina lectin recognizes a non-reducing terminal N-acetylneuraminic acid residue in glycoproteins and oligosaccharides. Binding of biotinyl P. velutina lectin to N-acetylneuraminic acid residues was prevented by desialylation of glycoconjugates and was distinguished from the binding to N-acetylglucosamine. Sialooligosaccharides were retarded or bound and eluted with N-acetylglucosamine on a P. velutina lectin column, being differentiated from each other and also from the oligosaccharides with non-reducing terminal N-acetylglucosamine which bound more strongly to the column.

Detection of lectins using ligand blotting and polyacrylamide-type glycoconjugate probes

A sensitive and convenient method for detection of the carbohydrate-binding activity of lectins was established using the combination of blotting of lectins on polyvinylidene difluoride membranes, carbohydrate-conjugated biotinylated polyacrylamide-type probes (carbohydrate-bp probes), horseradish peroxidase-streptavidin, and detection by enhanced chemiluminescence of the enzyme reaction. This method was tested for detection of four plant lectins blotted on the membrane: concanavalin A was detectable down to 100 ng by mannose-bp probe, Ricinus communis agglutinin 120 to as low as 5 ng by N-acetyllactosamine-bp probe, soybean agglutinin to 1 microgram by beta-N-acetyl-D-galactosamine-bp probe, and wheat germ agglutinin to 5 ng by beta-N-acetyl-D-glucosamine-bp probe. All four lectins were detectable on an electroblotted membrane after SDS-polyacrylamide gel electrophoresis. This method was used to detect recombinant human galectin-3 in Escherichia coli cell lysates and mannan-binding protein in human serum. These results indicate that this method is widely applicable to convenient detection and characterization of lectins in crude samples.

Amino acid sequence, glycan structure, and proteolytic processing of the lectin of Vatairea macrocarpa seeds

VML is a galactose-binding lectin isolated from Vatairea macrocarpa seeds. By SDS-polyacrylamide gel electrophoresis, VML is a glycoprotein composed of a major 32-34 kDa double band (alpha-chain) and minor 22 kDa and 13 kDa bands. N-terminal sequencing of electroblotted samples showed that the 22 and 13 kDa bands corresponded to C-(beta) and N-(gamma) terminal fragments of the alpha-chain, respectively. The primary structure of VML displays similarity with other leguminous lectins, particularly with Erythrina variegata, Robinia pseudoacacia and Sophora japonica lectins. VML is N-glycosylated at asparagine residues at positions 111 and 183 with one major glycan structure. Tandem mass spectrometry and methylation analysis indicated the presence of Manalpha1-6[(Manalpha1-3)(Xylbeta1-2)]Manbeta1-4 -GlcNAcbeta1-4(Fucalpha1-3)GlcNAc, a typical plant Nglycan. Equilibrium sedimentation analysis by analytical centrifugation showed that VML had a mass of 122-130 kDa, which did not change within the pH range 2.5-8.5. These data indicated that VML is a pH-independent homotetrameric protein and that a small proportion of the alpha-subunits is cleaved into noncovalently associated N- and C-terminal fragments. Mass spectrometric analysis suggested a mechanism for the proteolytic processing of VML. V. macrocarpa lectin contains a mixture of doubly (28,525 Da) and singly (27,354 Da) glycosylated alpha-chains. Deglycosylation of Asn-111 correlates with proteolytic cleavage of the Asn-114-Lys-115 bond yielding glycosylated gamma (residues 1-114, 12,304 Da) and nonglycosylated beta-(residues 115-239, 14,957 Da) chains. Some beta-chain molecules are further deglycosylated and N-terminally processed yielding products of molecular masses of 13,783 Da and 13,670 Da.

Legume lectin structure

The legume lectins are a large family of homologous carbohydrate binding proteins that are found mainly in the seeds of most legume plants. Despite their strong similarity on the level of their amino acid sequences and tertiary structures, their carbohydrate specificities and quaternary structures vary widely. In this review we will focus on the structural features of legume lectins and their complexes with carbohydrates. These will be discussed in the light of recent mutagenesis results when appropriate. Monosaccharide specificity seems to be achieved by the use of a conserved core of residues that hydrogen bond to the sugar, and a variable loop that determines the exact shape of the monosaccharide binding site. The higher affinity for particular oligosaccharides and monosaccharides containing a hydrophobic aglycon results mainly from a few distinct subsites next to the monosaccharide binding site. These subsites consist of a small number of variable residues and are found in both the mannose and galactose specificity groups. The quaternary structures of these proteins form the basis of a higher level of specificity, where the spacing between individual epitopes of multivalent carbohydrates becomes important. This results in homogeneous cross-linked lattices even in mixed precipitation systems, and is of relevance for their effects on the biological activities of cells such as mitogenic responses. Quaternary structure is also thought to play an important role in the high affinity interaction between some legume lectins and adenine and a series of adenine-derived plant hormones. The molecular basis of the variation in quaternary structure in this group of proteins is poorly understood.

Identification of a Fusobacterium nucleatum PK1594 galactose-binding adhesin which mediates coaggregation with periopathogenic bacteria and hemagglutination

Attachment of Fusobacterium nucleatum to various oral surfaces is mediated by several adhesins anchored on its outer surface. Monoclonal antibodies (MAbs) were prepared and used to identify the putative galactose-binding adhesin of F. nucleatum PK1594. Four unique MAbs, 8G7, 26B9, 28G11, and 29D4, were isolated on the basis of their ability to inhibit coaggregation of F. nucleatum PK1594 with Porphyromonas gingivalis PK1924. All four MAbs were also capable of inhibiting galactose-inhibitable interactions of F. nucleatum PK1594 with other oral gram-negative bacteria and with erythrocytes. Preincubation of F. nucleatum PK1594 with MAb 26B9 or its Fab fragments at concentrations lower than 1 microg/ml resulted in complete inhibition of coaggregation with P. gingivalis PK1924 or hemagglutination. F. nucleatum PK1594 surface components prepared by mild sonication or by extracting whole cells with detergents were subjected to Western blot analysis. None of the MAbs were able to recognize any polypeptide in these experiments. Therefore, detergent extracts of F. nucleatum PK1594 surface components were subjected to three experimental procedures: (i) separation by ion-exchange chromatography and testing of fractions for reaction with MAb 26B9 in an enzyme-linked immunosorbent assay (ELISA), (ii) lactose-Sepharose affinity chromatography and testing of the lactose eluate in ELISA with MAb 26B9, and (iii) immunoseparation with either MAb 26B9 or 8G7. Collectively, the results suggest that the putative adhesin is a 30-kDa outer membrane polypeptide which mediates the coaggregation with P. gingivalis PK1924 as well as other galactose-sensitive interactions of F. nucleatum PK1594.

Structures and contribution to the antigenicity of oligosaccharides of Japanese cedar (Cryptomeria japonica) pollen allergen Cry j I: relationship between the structures and antigenic epitopes of plant N-linked complex-type glycans

The oligosaccharide structures of Cry j I, a major allergenic glycoprotein of Cryptomeria japonica (Japanese cedar, sugi), were analysed by 400 MHz 1H-NMR and two-dimensional sugar mapping analyses. The four major fractions comprised a series of biantennary complex type N-linked oligosaccharides that share a fucose/xylose-containing core and glucosamine branches including a novel structure with a nongalactosylated fucosylglucosamine branch. Rabbit polyclonal anti-Cry j I IgG antibodies cross-reacted with three different plant glycoproteins having the same or shorter N-linked oligosaccharides as Cry j I. ELISA and ELISA inhibition studies with intact glycoproteins, glycopeptides and peptides indicated that both anti-Cry j I IgGs and anti-Sophora japonica bark lectin II (B-SJA-II) IgGs included oligosaccharide-specific antibodies with different specificities, and that the epitopic structures against anti-Cry j I IgGs include a branch containing alpha 1-6 linked fucose and a core containing fucose/xylose, while those against anti-B-SJA-II IgGs include nonreducing terminal mannose residues. The cross-reactivities of human allergic sera to miraculin and Clerodendron Trichotomum lectin (CTA) were low, and inhibition studies suggested that the oligosaccharides on Cry j I contribute little or only conformationally to the reactivity of specific IgE antibodies.

Purification and characterization of a pod lectin from Great Northern bean, Phaseolus vulgaris L

The pods of the Great Northern bean plant contain a lectin (GNpL) that highly resembles seed lectins (GNLs) of the same plant. Purification of GNpL from pod extracts was achieved by ion-exchange chromatographies on CM- and DEAE-celluloses and gel filtration chromatography on Sephacryl S-300 HR. GNpL has a similar SDS-PAGE pattern to that of GNLs. GNpL and GNLs yield three subunits though each GNpL subunit is 0.5 kDa smaller than the corresponding GNLs subunit (GNpL; pod-alpha-subunit of 34.0 kDa, pod-beta-subunit of 36.5 kDa, and pod-gamma-subunit of 38.5 kDa). GNpL and GNLs display indistinguishable carbohydrate specificities and have similar amino acid compositions. Pod-alpha-subunit cross-reacts with antibodies against GNLs on western blotting. On the other hand, the N-terminal amino acid sequence of pod-alpha-subunit suggests that GNpL is a distinct gene product from those of GNLs genes although they are shown to be homologous proteins.

A lectin and a lectin-related protein are the two most prominent proteins in the bark of yellow wood (Cladrastis lutea)

Using a combination of cDNA cloning and protein purification it is demonstrated that bark of yellow wood (Cladrastis lutea) contains two mannose/glucose binding lectins and a lectin-related protein which is devoid of agglutination activity. One of the lectins (CLAI) is the most prominent bark protein. It is built up of four 32 kDa monomers which are post-translationally cleaved into a 15 kDa and a 17 kDa polypeptide. The second lectin (CLAII) is a minor protein, which strongly resembles CLAI except that its monomers are not cleaved into smaller polypeptides. Molecular cloning of the Cladrastis lectin family revealed also the occurrence of a lectin-related protein (CLLRP) which is the second most prominent bark protein. Although CLLRP shows sequence homology to the true lectins, it is devoid of carbohydrate binding activity. Molecular modelling of the three Cladrastis proteins has shown that their three-dimensional structure is strongly related to the three-dimensional models of other legume lectins and, in addition, revealed that the presumed carbohydrate binding site of CLLRP is disrupted by an insertion of three extra amino acids. Since it is demonstrated for the first time that a lectin and a non-carbohydrate binding lectin-related protein are the two most prominent proteins in the bark of a tree, the biological meaning of their simultaneous occurrence is discussed.

Cloning of a lectin cDNA and seasonal changes in levels of the lectin and its mRNA in the inner bark of Robinia pseudoacacia

A cDNA clone encoding a lectin was isolated by immunological screening of an expression library prepared from poly(A)+ RNA from the inner bark of Robinia pseudoacacia. The cDNA clone (RBL104) had an open reading frame of 858 bp that encoded a polypeptide with a predicted molecular weight of 31210. This molecular weight corresponded closely to that of a polypeptide immunoprecipitated from products of translation in vitro of the poly(A)+ RNA. Thus, RBL104 appeared to be a full-length cDNA. The N-terminal amino acid sequence of the purified lectin protein matched a portion of the predicted amino acid sequence. It appeared that the lectin was synthesized as a precursor that consisted of a putative signal peptide of 31 amino acids and a mature polypeptide of 255 amino acids. Southern blot analysis of the genomic DNA revealed that the lectin was encoded by a small multigene family. The lectin was mostly localized in the axial and ray parenchymal cells of the inner bark. A small amount of lectin was also found in the axial and ray parenchymal cells of the xylem. The lectin accumulated in the inner bark in September, remained at high levels during the winter and disappeared in May. The mRNA for the lectin was detected from August to the following March. The appearance and disappearance of the mRNA were observed prior to those of the lectin protein.

Purification and characterization of novel lectins from Great Northern bean, Phaseolus vulgaris L

Two lectins, GNL-1 and 2, were isolated from extracts of Great Northern bean powder through fractionation with ammonium sulfate, ion-exchange chromatographies on CM- and DEAE-celluloses, and gel filtration chromatography on Sephacryl S-200 HR. These lectins were shown to be homogenous by gel electrophoresis, gel filtration, and isoelectric focusing. The lectins (GNL-1 and 2) have molecular masses of 175 and 145 kDa on gel filtration, respectively. They yield three bands having the respective same molecular masses on SDS-PAGE (GNL-1; alpha-subunit of 34.5 kDa, beta of 37.0, and gamma of 39.0: GNL-2; alpha' of 34.5 kDa, beta' of 37.0, and gamma' of 39.0). Two lectins are shown to be glycoproteins and the carbohydrate contents of GNL-1 and 2 are 5.1 and 4.5%, respectively. The isoelectric points are 5.5 and 5.1 and the extinction coefficients (A 1cm 1%) at 280 nm are 11.37 and 11.45, respectively. These lectins are nonspecific in agglutination for rabbit and any types of human erythrocytes. Inhibition study shows no specificity against mono and disaccharides. On the other hand, binding assay of horseradish peroxidase-glycoproteins to the bands electroblotted onto PVDF membrane reveals that all of the subunits can bind to sugar moieties in fetuin, asialofetuin, and porcine thyroglobulin specifically. Moreover, assay of mitogenic activity shows that GNL-1 is a strong mitogen, but GNL-2 is lack of the activity.

Bowringia mildbraedii agglutinin: polypeptide composition, primary structure and homologies with other legume lectins

The amino-acid sequences of the subunits of the lectin BMA from seeds of Bowringia mildbraedii have been determined. The data indicate that the lectin consists of a precursor polypeptide of approx. 29 kDa that is cleaved almost completely into two fragments of approx. 13.3 kDa (alpha subunit) and approx. 11.9 kDa (beta subunit), respectively. The beta subunit represents the N-terminal half of precursor polypeptides and is disulphide-linked in a beta beta dimer in the native (alpha beta)2 protein. BMA shows extensive amino-acid sequence homologies with known legume lectins. The site of post-translational proteolysis of the putative precursor occurs at a position similar to that identified in lectins obtained from other Sophoreae plants such as Sophora japonica and in Diocleae lectins such as Concanavalin A, but different from that of two chain lectins obtained from other tribes of the Papilionaceae.

Affinity purification and affinity characterization of carbohydrate-binding proteins in bovine kidney

Ca(2+)-dependent carbohydrate-binding proteins were purified from bovine kidney by two-step affinity chromatography on fetuin and heparin columns and subsequent anion-exchange high-performance liquid chromatography. On sodium dodecyl sulphate-polyacrylamide gel electrophoresis, the purified fraction gave two protein bands corresponding to proteins of relative molecular mass 33,000 (p33) and 41,000 (p41), respectively. Although the proteins had no haemogglutinating activities towards human and rabbit erythrocytes, their carbohydrate-binding activity was examined by a newly developed method using horseradish peroxidase (HRP) and/or biotin-labelled glycoconjugates as affinity probes. They could bind in a Ca(2+)-dependent manner to labelled fetuin and heparin in a specific and dose-dependent manner by solid-phase assay after immobilization on plastic plate surface. Inhibition assay of the binding revealed that N-acetylneuraminic acid is the most potent inhibitor of the proteins among the monosaccharides tested. Fucoidin and heparan sulphate most strongly inhibited the binding of the proteins to labelled heparin. Direct binding assay to acidic glycolipids prepared from bovine kidney showed that the proteins react with the ganglioside fraction but not with sulphatide [Gal(3-SO4) beta 1-1Cer]. These results indicated that the purified proteins have a significant affinity to charged oligosaccharides linking to glycoproteins, glycolipids and charged polysaccharides in a Ca(2+)-dependent manner.

Improved affinity chromatographic purification of D-mannose-N-acetyl-D-glucosamine-specific lectin from the bark of Sophora japonica eliminating the loss by sugar specific self-aggregation

A novel D-mannose-N-acetyl-D-glucosamine-specific lectin of Sophora japonica bark, B-SJA-II, which showed self-aggregation based on sugar specificity, was purified by affinity chromatography on maltamyl-Sepharose subsequent to chromatographic separation on lactamyl-Sepharose to remove a major D-galactose-N-acetyl-D-galactosamine specific lectin, B-SJA-I. However, the yield of this method was low as a result of the sugar-specific precipitation and binding to other glycoproteins. A modified method was developed to circumvent this problem. All the purification procedures, except for the final chromatographic separation, were carried out in the presence of the haptenic sugar and the sugar-specific adsorption of B-SJA-II onto the adsorbent was carried out in a dialysis bag by gradually removing the sugar. This method gave a yield eight times higher than the original method.

Carbohydrate analysis

The analysis of the carbohydrate chains attached to proteins is becoming increasingly important as appreciation of the role of glycosylation in the structural and functional properties of biologically significant glycoproteins grows. Over the past year, a number of developments have been made that may improve and promote the analysis of the glycosylation of proteins.