Mannose-binding Sites Research Articles

Characterization of a mannose-binding lectin gene from Typhonium divaricatum (L.) Decne

Monocot mannose-binding lectins (MMBLs) or agglutinins are an extended superfamily of structurally and evolutionarily related proteins and they play important roles in plant defenses. Here the full-length cDNA of monocot mannose-binding agglutinin (designated as TDA, GenBank accession no.: AY347940) was isolated from Typhonium divaricatum, a traditional Chinese medicinal herb. Sequence analysis revealed that the full-length cDNA of TDA was 870 bp, and had a 594 bp open reading frame (ORF) encoding a putative 197-aa agglutinin precursor with a C-terminal domain. Multiple alignments of TDA amino acids with those of seven other MMBLs revealed three highly conserved domains among them, indicating TDA belongs to a member of the MMBL superfamily. Predicted tertiary structure analysis showed that TDA had three potential equal mannose-binding sites. Phylogenetic analysis indicated that 20 MMBLs including TDA belonged to an extended superfamily. Northern blot analysis showed that TDA expressed in T. divaricatum in a tissue-specific manner, with highest expression in tuber and almost no expression in petiole and leaf. The cloning and characterization of TDA will enable us to study its potential insect resistance function in the future

Structures of the Carbohydrate Recognition Domain of Ca2+-independent Cargo Receptors Emp46p and Emp47p

Emp46p and Emp47p are type I membrane proteins, which cycle between the endoplasmic reticulum (ER) and the Golgi apparatus by vesicles coated with coat protein complexes I and II (COPI and COPII). They are considered to function as cargo receptors for exporting N-linked glycoproteins from the ER. We have determined crystal structures of the carbohydrate recognition domains (CRDs) of Emp46p and Emp47p of Saccharomyces cerevisiae, in the absence and presence of metal ions. Both proteins fold as a beta-sandwich, and resemble that of the mammalian ortholog, p58/ERGIC-53. However, the nature of metal binding is distinct from that of Ca(2+)-dependent p58/ERGIC-53. Interestingly, the CRD of Emp46p does not bind Ca(2+) ion but instead binds K(+) ion at the edge of a concave beta-sheet whose position is distinct from the corresponding site of the Ca(2+) ion in p58/ERGIC-53. Binding of K(+) ion to Emp46p appears essential for transport of a subset of glycoproteins because the Y131F mutant of Emp46p, which cannot bind K(+) ion fails to rescue the transport in disruptants of EMP46 and EMP47 genes. In contrast the CRD of Emp47p binds no metal ions at all. Furthermore, the CRD of Emp46p binds to glycoproteins carrying high mannosetype glycans and the is promoted by binding not the addition of Ca(2+) or K(+) ion in These results suggest that Emp46p can be regarded as a Ca(2+)-independent intracellular lectin at the ER exit sites.

Carbohydrate-binding site of a novel mannose-specific lectin from fugu ( Takifugu rubripes) skin mucus

Pufflectin-s, identified in the skin mucus of the fugu Takifugu rubripes, is a novel mannose-specific lectin with similar structure to monocotyledonous plant lectins. In the present study, mutational analysis was used to reveal the mannose-binding sites of pufflectin-s. Putative binding sites were mutated as follows: binding site 1; rPL-D32E (Asp 32 → Glu 32), rPL-N34S (Asn 34 → Ser 34) and rPL-V36A (Val 36 → Ala 36) whereas binding site 2; rPL-D61E (Asp 61 → Glu 61), rPL-N63S (Asn 63 → Ser 63) and rPL-V65A (Val 65 → Ala 65). All recombinant proteins were expressed in Escherichia coli, purified with two chromatographic steps, and then subjected to mannose-binding assay by affinity chromatography. Recombinant wild-type pufflectin-s (rPL-wt) as well as three mutants with changes in binding site 2 could bind to mannose, in contrast to the three mutants with changes in binding site 1 in which mannose-binding activity was completely lost. These results clearly demonstrate that, at the least, binding site 1 is critical to mannose-binding activity in pufflectin-s.

Anti-HIV I/II Activity and Molecular Cloning of a Novel Mannose/Sialic Acid-binding Lectin from Rhizome of <italic>Polygonatum cyrtonema</italic> Hua

The anti-human immunodeficiency virus (HIV) I/II activity of a mannose and sialic acid binding lectin isolated from rhizomes of Polygonatum cyrtonema Hua was elucidated by comparing its HIV infection inhibitory activity in MT-4 and CEM cells with that of other mannose-binding lectins (MBLs). The anti-HIV activity of Polygonatum cyrtonema Hua lectin (PCL) was 10- to 100-fold more potent than other tested MBLs, but without significant cytotoxicity towards MT-4 or CEM cells. To amplify cDNA of PCL by 3'/5'-rapid amplification of cDNA ends (RACE), the 30 amino acids of N-terminal were determined by sequencing and the degenerate oligonucleotide primers were designed. The full-length cDNA of PCL contained 693 bp with an open reading frame encoding a precursor protein of 160 amino acid residues, consisting of a 28-residue signal peptide, a 22-residue C-terminal cleavage peptide and a 110-residue mature polypeptide which contained three tandemly arranged subdomains with an obvious sequence homology to the monocot MBL. However, only one active mannose-binding site (QDNVY) was found in subdomain I of PCL, that of subdomain II and III changed to HNNVY and PDNVY, respectively. There was no intron in PCL, which was in good agreement with other monocot MBLs. Molecular modeling of PCL indicated that its three-dimensional structure resembles that of the snowdrop agglutinin. By docking, an active sialic acid-binding site was found in PCL. The instabilization of translation initiation region (TIR) in mRNA of PCL benefits its high expression in rhizomes.

Synthesis of Cluster Mannosides Carrying a Photolabile Diazirine Group

AbstractWe are investigating the mechanisms underlying the carbohydrate‐specific adhesion of bacteria such as Escherichia coli to the glycocalyx of their potential host cells. E. coli possess protein appendages, which are called type 1 fimbriae. Part of type 1 fimbriae is a protein named FimH, which is a mannose‐specific lectin. We wish to use photoaffinity labeling to elucidate mannose binding sites on FimH. Thus we report the synthesis of di‐ and trivalent cluster mannosides, which carry a photolabile diazirine group. The diazirine group was introduced by a convergent approach using thiourea bridging (products 6, 13, 17, and 27) or in a divergent synthesis leading to the divalent cluster mannoside 31. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Cloning and Characterization of an Agglutinin Gene from Arisaema lobatum

A novel agglutinin gene was cloned from Arisaema lobatum using SMART RACE-PCR technology. The full-length cDNA of Arisaema lobatum agglutinin (ala) was 1078 bp and contained a 774 bp open reading frame encoding a lectin precursor (proproprotein) of 258 amino acid residues with a 23 aa signal peptide. ALA contained three mannose-binding sites (QXDXNXVXY) with two-conserved domains of 45% identity, ALA-DOM1 and ALA-DOM2. The three-dimensional structure of ALA was very similar to that of GNA (Galanthus nivalis agglutinin). ALA shared varying identities, ranging from 40% to 85%, with mannose-binding lectins from other species of plant families, such as Araceae, Alliaceae, Iridaceae, Lillaceae, Amaryllidaceae and Bromeliaceae. Genomic sequence of ala was also cloned using genomic walker technology, and it was found to contain three putative TATA boxes and eight possible CAAT boxes in the 5'-flanking region. No intron was found within the region of genomic sequence. Southern blot analysis indicated that the ala belonged to a multi-copy gene family. Expression pattern analysis revealed that the ala preferentially expressed in the tissues with the higher expression being found in spadix, bud, leaf, spathe and tuber. The cloning of the ala gene not only provides a basis for further investigation of its structure, expression and regulation mechanism, but also enables us to test its potential role in controlling pests and fungal diseases by transferring the gene into plants in the future.

Binding of recombinant human proacrosin/acrosin to zona pellucida glycoproteins. II. Participation of mannose residues in the interaction

To assess the interaction of human proacrosin/acrosin with mannose residues coupled to a protein backbone. Prospective study. Basic research laboratory. Recombinant proteins derived from human proacrosin (Rec-40, Rec-30, Rec-20, Rec-10, and Rec-6) and bovine serum albumin (BSA)-mannose as ligand. In vitro binding assay developed to assess proacrosin/acrosin-BSA-mannose interaction. Proacrosin/acrosin binding to BSA-mannose; estimation of binding affinity. All recombinant proteins of acrosin but Rec-6 (residues 1-59 of proacrosin) specifically bound to BSA-mannose. Rec-40 (proacrosin) showed the highest binding affinity (dissociation constant K(d), 162 nM), followed by N-terminal fragments Rec-30 (248 nM), Rec-20 (359 nM), and Rec-10 (402 nM). A significant decrease in binding activity was observed when acrosin proteins were treated with denaturing agents such as urea or heat. The beta-mercaptoethanol treatment produced a 39% decrease on Rec-30 binding to BSA-mannose; in contrast, no effect was observed with Rec-40, suggesting the presence of at least two types of mannose-binding sites. [1] Proacrosin interacts with mannose residues through binding sites located at both the N- and C-terminal portion of the protein, [2] the full-length protein is required for maximal BSA-mannose binding, and [3] binding sites are stabilized by noncovalent bonds and by disulfide linkages.

Spermadhesin AQN1 Is a Candidate Receptor Molecule Involved in the Formation of the Oviductal Sperm Reservoir in the Pig1

Sperm are stored in the isthmic region of the oviduct under conditions that maintain viability and suppress early capacitation steps until ovulation occurs. The initial contact between sperm and oviductal epithelium is mediated by carbohydrate-protein interactions. In the pig, the carbohydrate recognition system has been shown to involve oligomannosyl structures. The spermadhesins AWN and AQN1 are the dominant porcine carbohydrate-binding sperm proteins. The objective of this study was to demonstrate that AQN1 contributes to sperm binding to the oviductal epithelium. AQN1 showed a broad carbohydrate-binding pattern as it recognizes both alpha- and beta-linked galactose as well as Manalpha1-3(Manalpha1-6)Man structures, whereas AWN bound only the galactose species. Binding of ejaculated sperm to oviductal epithelium was inhibited by addition of AQN1 but not by AWN. Mannose-binding sites were localized over the rostral region of the sperm head. Flow cytometry showed that, under capacitating conditions, the population of live sperm was shifted within 30 min toward an increase in the proportion of cells with low mannose- and high galactose-binding. The loss of mannose-binding sites was accompanied by the loss of AQN1 in sperm extracts and the significant reduction in the sperm-oviduct binding. The oviductal epithelium was shown by GNA-lectin histochemistry and by SDS-PAGE and lectin blotting of the apical membrane fraction to express mannose components that could be recognized by AQN1. These results demonstrate that the sperm lectin AQN1 fulfils the criteria for an oviduct receptor in the pig and may play a role in the formation of the oviductal sperm reservoir.

Characterization of a jasmonate-regulated wheat protein related to a beta-glucosidase-aggregating factor

Jasmonates are distributed throughout higher plants, where they play an important role in the activation of signal transduction pathways in response to wounding and pathogen attack. Jasmonates are known to induce the transcriptional activation of plant defense genes, produce jasmonate-regulated proteins (JRP). One class of 32 kDa JRP (designated as JRP-32 in this paper) is present in the Gramineae family, although the function of these proteins is still unclear. A cDNA was cloned from wheat ( Triticum aestivum L.) and designated as Ta-JA1. Sequence comparison indicated that Ta-JA1 encodes a JRP-32 protein. Ta-JA1 exists as a single-copy gene, but other genes with low sequence similarity to Ta-JA1 may be present in the wheat genome. The expression of Ta-JA1 was confined to stem tissues and barely detected in leaf and root tissues. Western blot analyses demonstrated that the recombinant Ta-JA1 protein cross-reacts with maize beta-glucosidase-aggregating factor (BGAF) antibody. Molecular modeling showed that Ta-JA1 and BGAF have a very similar three-dimensional structure. Protein structure analysis indicated that Ta-JA1 together with some related proteins (maize BGAF, wheat Ver2, WCI-1 and Hfr-1) contain two functional domains: a disease response domain and jacalin-related lectin (JRL) domain. A mannose-binding site was also well conserved in these proteins. The data support the hypothesis that JRP-32 and related proteins from Gramineae form a small protein family related to JRLs. This small protein family may have evolved from mannose-specific jacalin-related lectins (mJRLs) by developing a disease response domain in their N-terminus, which may have broadened the functional role of these proteins to include the plant defense response.

Cloning and expression of a novel cDNA encoding a mannose-binding lectin from Dendrobium officinale

Using RNA extracted from Dendrobium officinale young leaves and primers designed according to the conservative regions of orchidaceae lectins, the full-length cDNA of Dendrobium officinale agglutinin2 (DOA2) was cloned by rapid amplification of cDNA ends (RACE). The full-length cDNA of doa2 was 777 bp and contained a 513 bp open reading frame (ORF) encoding a lectin precursor of 170 amino acids. Through comparative analysis of doa2 gene and its deduced amino acid sequence with those of other orchidaceae species and Amaryllidaceae species, it was found that DOA2 had many common characters of mannose-binding lectin superfamily including three mannose-binding sites. Semi-Quantitative RT-PCR analysis revealed that doa2 mRNA expression was detected in all tested tissues including root, stem and leaf, however, the expression was higher in stem, and lower in leaf. As the doa2 mRNA was detected in all the tested plant tissues, the doa2 was considered to be a constitutively expressed gene. The recombinant protein was expressed in E. coli and purified. Anti-fungal assay showed that DOA2 has anti-fungal activity towards Gibberella zeae. To our knowledge, this is the first report on cDNA cloning of mannose binding lectin from Dendrobium officinale.

Molecular cloning and characterization of a novel mannosebinding lectin cDNA from Zantedeschia aethiopica

Using RNA extracted from Zantedeschia aethiopica young leaves and primers designed according to the conservative regions of Araceae lectins, the full-length cDNA of Z. aethiopica agglutinin (ZAA) was cloned by rapid amplification of cDNA ends (RACE). The full-length cDNA of zaa was 871 bp and contained a 417 bp open reading frame (ORF) encoding a lectin precursor of 138 amino acids. Through comparative analysis of zaa gene and its deduced amino acid sequence with those of other Araceae species, it was found that zaa encoded a precursor lectin with signal peptide. Secondary and three-dimensional structure analyses showed that ZAA had many common characters of mannose-binding lectin superfamily and ZAA was a mannose-binding lectin with three mannose-binding sites. Southern blot analysis of the genomic DNA revealed that zaa belonged to a multi-copy gene family.

Molecular Cloning and Characterization of a Mannose-binding Lectin Gene from Dendrobium officinale

Using RNA extracted from Dendrobium officinale young leaves and primers designed according to the conservative regions of Orchidaceae lectins, the full-length cDNA of Dendrobium officinale agglutinin (DOA) was cloned by rapid amplification of cDNA ends (RACE). The full-length cDNA of doa was 768 bp and contained a 498 bp open reading frame (ORF) encoding a lectin precursor of 165 amino acids. Through comparative analysis of doa gene and its deduced amino acid sequence with those of other Orchidaceae species, it was found that doa encoded a precursor lectin with signal peptide. DOA was a mannose-binding lectin with three mannose-binding sites. Semi-quantitative RT-PCR analysis revealed that doa mRNA expression was detected in all tested tissues including root, stem and leaf, however, the expression was higher in stem, lower in leaf. As the doa mRNA was detected in all the tested plant tissues, the doa was considered to be a constitutively expressed gene.

The Site-Directed Mutagenesis of Gastrodia Anti-Fungal Protein Mannose-Binding Sites and Its Expression in Escherichia Coli

Gastrodia anti-fungal protein (GAFP) displays strong inhibitory activity against certain fungal pathogens. Five GAFP analogues with different mutations at mannose-binding sites and the wild-type one were expressed and purified in Escherichia coli. The inhibitory analysis of the purified various GAFPs against the growth of Trichoderma viride indicates that single amino acid mutated-type GAFPs have inhibitory activity, but its activity is much less than the wild-type one. The double and triplicate amino acids mutated GAFPs have very low inhibitory activity. For the first time it was proved that GAFP mannose-binding sites play key role in anti-fungi process.

Molecular Cloning of a New Lectin Gene fromZ. grandiflora

Using RNA extracted from Zephyrathes grandiflora young leaves and primers designed according to the conservative regions of Amaryllidaceae lectins, the full-length cDNA of Z. grandiflora agglutinin (ZGA) was cloned by rapid amplification of cDNA ends (RACE). The full-length cDNA of ZGA was 934 bp and contained a 576 bp open reading frame (ORF) encoding a 191 amino acid protein. Through comparative analysis of zga gene and its deduced amino acid sequence with those of other Amaryllidaceae species, it was found that zga encoded a precursor lectin with signal peptide. Molecular modeling suggested that ZGA was a mannose-binding lectin with three mannose-binding sites like lectins from other Amaryllidaceae species. Southern blot analysis of the genomic DNA revealed that zga belonged to a multi-copy gene family like those of many other Amaryllidaceae species such as Galanthus nivalis and Clivia miniata.

Molecular cloning and characterization of a mannose-binding lectin gene from Crinum asiaticum

Full-length cDNA of a mannose-binding lectin or agglutinin gene was cloned from a traditional Chinese medicinal herb Crinum asiaticum var. sinicum through RACE-PCR cloning. The full-length cDNA of C. asiaticum agglutinin (caa) was 820 bp and contained a 528 bp open reading frame encoding a lectin precursor (preproprotein) of 175 amino acid residues with a 22 aa signal peptide. The coding region of the caa gene was high in G/C content. The first 20 bp of the 5' UTR had a dC content of 50%, which was a typical feature of the leader sequence. By cutting away the signal peptide, the CAA proprotein was 15.79 kDa with a pl of 9.27 and contained 3 mannose-binding sites (QDNY). Random coil and extended strand constituted interlaced domination of the main part of the secondary structure. B-lectin conserved domain existed within N24 to G130. Predicted three-dimensional structure of CAA proprotein was very similar to that of GNA (Galanthus nivalis agglutinin). It is significant that besides certain homologies to known monocot mannose-binding lectins from Amaryllidaceae, Orchidaceae, Alliaceae and Liliaceae, caa also showed high similarity to gastrodianin type antifungal proteins. No intron was detected within the region of genomic sequence corresponding to the caa full-length cDNA. Southern blot analysis indicated that the caa gene belonged to a low-copy gene family. Northern blot analysis demonstrated that caa mRNA was constitutively expressed in all the tested tissue types including the root, bulb, leaf, rachise, flower and fruit tissues.

Sperm surface hyaluronan binding protein (HABP1) interacts with zona pellucida of water buffalo (Bubalus bubalis) through its clustered mannose residues.

Sperm-oocyte interaction during fertilization is multiphasic, with multicomponent events, taking place between zona pellucida (ZP) glycoproteins and sperm surface receptor. d-mannosylated glycoproteins, the major constituents of ZP are considered to serve as ligands for sperm binding. The presence of hyaluronan binding protein 1 (HABP1) on sperm surface of different mammals including cattle and its possible involvement in sperm function is already reported. Recently, we have demonstrated the specificity of clustered mannose as another ligand for HABP1 (Kumar et al., 2001: J Biosci 26:325-332). Here, we report that only N-linked mannosylated zona-glycoproteins bind to sperm surface HABP1. Labeled HABP1 interacts with ZP of intact oocyte of Bubalus bubalis, which can be competed with unlabeled HABP1 or excess d-mannosylated albumin (DMA). This data suggests the specific interaction of HABP1 with ZP, through clustered mannose residues. In order to examine the physiological significance of such an interaction, the capacity of sperm binding to oocytes under in vitro fertilization plates was examined either in presence of DMA alone or in combination with HABP1. The number of sperms, bound to oocytes was observed to reduce significantly in presence of DMA, which could be reversed by the addition of purified recombinant HABP1 (rHABP1) in the same plate. This suggests that sperm surface HABP1 may act as mannose binding sites for zona recognition.

Mannosides as crucial part of bioactive supports for cultivation of human epidermal keratinocytes without feeder cells

Large-scale production of keratinocytes by cell culture is of interest for medical applications. Long-term cultivation of epidermal cells is presently possible with feeder cells, i.e. 3T3 fibroblasts with arrested mitosis, or with specially formulated culture medium. To define refinements for in vitro conditions, the analysis of the natural environment with growth-maintaining/stimulating factors can provide important clues. Cells with proliferative activity are located in the basal layer of the epidermis in close contact with a basement membrane. Employing lectin and reverse lectin histochemistry of skin, muscle fibers and feeder cells, we assumed that the interplay of mannose-binding sites of epidermal cells, detected by a labeled neoglycoprotein, with glycoligands in the feeder cell layer or basement membrane could trigger signaling with relevance for adhesion and growth regulation. Indeed, coating of polystyrene with mannose-containing neoglycoprotein mimicking a mannose-rich cell matrix enabled the cultivation of keratinocytes without feeder cells in a Ca 2+—dependent manner in serum—containing culture medium. Following this experimental demonstration of specific binding of mannose residues as part of a neoglycoprotein controlled by testing sugar-free carrier protein and other substances, we next synthesized and tested biocompatible polymers. Attachment and proliferation of keratinocytes on the surface of these polymers compared favorably to control experiments using feeder cells. In conclusion, we suggest that these polymers are bioactive offering a perspective for keratinocyte cultivation without feeder cells.

Similarities and differences in lectin cytochemistry of laryngeal and tracheal epithelium and subepithelial seromucous glands in cases of sudden infant death and controls

BACKGROUNDIt has been speculated that non-specific defence mechanisms of the epithelium and subepithelial seromucous glands play a role in the larynx and lungs in cases of sudden infant death.METHODSThe larynx...

Physiological state of bull sperm affects fucose- and mannose-binding properties.

In cattle, sperm are stored in a reservoir in the caudal isthmus of the oviduct until the time of ovulation approaches. Bull sperm are trapped in the reservoir by binding to fucosylated molecules on the oviductal epithelium. Capacitated sperm lose binding affinity for the epithelium; therefore this study was undertaken to determine whether this occurs because capacitated bull sperm lose binding affinity for fucose. BSA conjugated to alpha-L-fucopyranosylphenyl isothiocyanate and fluorescein isothiocyanate (fuc-BSA-FITC) was used in conjunction with flow cytometry to monitor the capacity of bull sperm to bind fucose. Dead sperm were identified using ethidium homodimer and were excluded from analysis. BSA-FITC conjugated with mannose (man-BSA-FITC) and BSA-FITC were used as controls. When examined by epifluorescence microscopy, motile bull sperm that exhibited labeling by any of the probes were fluorescent over the acrosomal region of the plasma membrane. By flow cytometry, labeling of live sperm was greatest for sperm that had been washed in TALP medium and probed with fuc-BSA-FITC (mean +/- SD:167 +/- 6.0 relative fluorescence units, collected in logarithmic mode). Labeling by fuc-BSA-FITC was lower in unwashed sperm (60 +/- 2.7) and in washed sperm with seminal plasma added back (56 +/- 8.0). Labeling was also reduced by centrifuging washed sperm through a Percoll step gradient (103 +/- 6.3) and by capacitating washed sperm in medium containing 10 microg/ml heparin (50 +/- 4.4). BSA-FITC labeling was barely detectable in all treatments. Man-BSA-FITC produced little labeling of washed sperm (22 +/- 0.6), as expected; however, intense labeling appeared over the acrosomal region of sperm incubated under capacitating conditions (128 +/- 21.6). It was concluded that removal of seminal plasma exposes fucose-binding sites, which are then lost or modified during capacitation, thereby allowing the release of sperm from the reservoir. At that time, mannose-binding sites are revealed or activated, which might serve to bind sperm to the zona pellucida.

Crystal Structure of a Dimeric Mannose-specific Agglutinin from Garlic: Quaternary Association and Carbohydrate Specificity

A mannose-specific agglutinin, isolated from garlic bulbs, has been crystallized in the presence of a large excess of α- d -mannose, in space group C 2 and cell dimensions, a=203.24, b =43.78, c=79.27 Å, β=112.4 °, with two dimers in the asymmetric unit. X-ray diffraction data were collected up to a nominal resolution of 2.4 Å and the structure was solved by molecular replacement. The structure, refined to an R -factor of 22.6 % and an R freeof 27.8 % reveals a β-prism II fold, similar to that in the snowdrop lectin, comprising three antiparallel four-stranded β-sheets arranged as a 12-stranded β-barrel, with an approximate internal 3-fold symmetry. This agglutinin is, however, a dimer unlike snowdrop lectin which exists as a tetramer, despite a high degree of sequence similarity between them. A comparison of the two structures reveals a few substitutions in the garlic lectin which stabilise it into a dimer and prevent tetramer formation. Three mannose molecules have been identified on each subunit. In addition, electron density is observed for another possible mannose molecule per dimer resulting in a total of seven mannose molecules in each dimer. Although the mannose binding sites and the overall structure are similar in the subunits of snowdrop and garlic lectin, their specificities to glycoproteins such as GP120 vary considerably. These differences appear, in part, to be a direct consequence of the differences in oligomerisation, implying that variation in quaternary association may be a mode of achieving oligosaccharide specificity in bulb lectins.