Soluble 14-kDa beta-galactoside-specific bovine lectin. Evidence from mutagenesis and proteolysis that almost the complete polypeptide chain is necessary for integrity of the carbohydrate recognition domain

Engineering the ligand specificity of the human galectin-1 by incorporation of tryptophan analogs

Galectin-1 is a β-galactoside-binding lectin with manifold biological functions. A single tryptophan residue (W68) in its carbohydrate binding site plays a major role in ligand binding and is highly conserved among galectins. To fine tune galectin-1 specificity, we introduced several non-canonical tryptophan analogs at this position of human galectin-1 and analyzed the resulting variants using glycan microarrays. Two variants containing 7-azatryptophan and 7-fluorotryptophan showed a reduced affinity for 3'-sulfated oligosaccharides. Their interaction with different ligands was further analyzed by fluorescence polarization competition assay. Using molecular modeling we provide structural clues that the change in affinities comes from modulated interactions and solvation patterns. Thus, we show that the introduction of subtle atomic mutations in the ligand binding site of galectin-1 is an attractive approach for fine-tuning its interactions with different ligands.

Tissue-specific control of galectin-1-driven circuits during inflammatory responses

The relevance of glycan-binding protein in immune tolerance and inflammation has been well established, mainly by studies of C-type lectins, siglecs and galectins both in experimental models and patient samples. Galectins, a family of evolutionarily conserved lectins, are characterized by sequence homology in the carbohydrate-recognition domain (CRD), atypical secretion via an ER-Golgi-independent pathway and the ability to recognize β-galactoside-containing saccharides. Galectin-1 (Gal-1), a prototype member of this family displays mainly anti-inflammatory and immunosuppressive activities, although, similar to many cytokines and growth factors, it may also trigger paradoxical pro-inflammatory effects under certain circumstances. These dual effects could be associated to tissue-, time- or context-dependent regulation of galectin expression and function, including particular pathophysiologic settings and/or environmental conditions influencing the structure of this lectin, as well as the availability of glycosylated ligands in immune cells during the course of inflammatory responses. Here, we discuss the tissue-specific role of Gal-1 as a master regulator of inflammatory responses across different pathophysiologic settings, highlighting its potential role as a therapeutic target. Further studies designed at analyzing the intrinsic and extrinsic pathways that control Gal-1 expression and function in different tissue microenvironments may contribute to design tailored therapeutic strategies aimed at positively or negatively modulate this glycan-binding protein in pathologic inflammatory conditions.

Galectin-Glycan Interactions: Guidelines for Monitoring by 77 Se NMR Spectroscopy, and Solvent (H2 O/D2 O) Impact on Binding

Functional pairing between cellular glycoconjugates and tissue lectins like galectins has wide (patho)physiological significance. Their study is facilitated by nonhydrolysable derivatives of the natural O‐glycans, such as S‐ and Se‐glycosides. The latter enable extensive analyses by specific ⁷⁷Se NMR spectroscopy, but still remain underexplored. By using the example of selenodigalactoside (SeDG) and the human galectin‐1 and ‐3, we have evaluated diverse ⁷⁷Se NMR detection methods and propose selective ¹H,⁷⁷Se heteronuclear Hartmann–Hahn transfer for efficient use in competitive NMR screening against a selenoglycoside spy ligand. By fluorescence anisotropy, circular dichroism, and isothermal titration calorimetry (ITC), we show that the affinity and thermodynamics of SeDG binding by galectins are similar to thiodigalactoside (TDG) and N‐acetyllactosamine (LacNAc), confirming that Se substitution has no major impact. ITC data in D₂O versus H₂O are similar for TDG and LacNAc binding by both galectins, but a solvent effect, indicating solvent rearrangement at the binding site, is hinted at for SeDG and clearly observed for LacNAc dimers with extended chain length.

Chicken GRIFIN: Structural characterization in crystals and in solution

Despite its natural abundance in lenses of vertebrates the physiological function(s) of the galectin-related inter-fiber protein (GRIFIN) is (are) still unclear. The same holds true for the significance of the unique interspecies (fish/birds vs mammals) variability in the capacity to bind lactose. In solution, ultracentrifugation and small angle X-ray scattering (at concentrations up to 9 mg/mL) characterize the protein as compact and stable homodimer without evidence for aggregation. The crystal structure of chicken (C-)GRIFIN at seven pH values from 4.2 to 8.5 is reported, revealing compelling stability. Binding of lactose despite the Arg71Val deviation from the sequence signature of galectins matched the otherwise canonical contact pattern with thermodynamics of an enthalpically driven process. Upon lactose accommodation, the side chain of Arg50 is shifted for hydrogen bonding to the 3-hydroxyl of glucose. No evidence for a further ligand-dependent structural alteration was obtained in solution by measuring hydrogen/deuterium exchange mass spectrometrically in peptic fingerprints. The introduction of the Asn48Lys mutation, characteristic for mammalian GRIFINs that have lost lectin activity, lets labeled C-GRIFIN maintain capacity to stain tissue sections. Binding is no longer inhibitable by lactose, as seen for the wild-type protein. These results establish the basis for detailed structure-activity considerations and are a step to complete the structural description of all seven members of the galectin network in chicken.

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First crystal structure of an eye lens GRIFIN defines differences to galectins.

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pH screening discloses high degree of structural stability in crystals.

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Hydrogen-deuterium exchange reveals unusually rigid structure in solution.

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Lectin histochemical assays identify critical sites for in situ ligand binding.

Key regulators of galectin-glycan interactions

Protein-ligand interactions serve as fundamental regulators of numerous biological processes. Among protein-ligand pairs, glycan binding proteins (GBPs) and the glycans they recognize represent unique and highly complex interactions implicated in a broad range of regulatory activities. With few exceptions, cell surface receptors and secreted proteins are heavily glycosylated. As these glycans often represent highly regulatable post-translational modifications, alterations in glycosylation can fundamentally impact GBP recognition. Among GBPs, galectins in particular appear to engage a diverse set of glycan determinants to impact a broad range of biological processes. In this review, we will explore factors that impact galectin activity, including the effect of glycan modification on galectin-glycan interactions.

Galectin-1 dimers can scaffold Raf-effectors to increase H-ras nanoclustering

Galectin-1 (Gal-1) dimers crosslink carbohydrates on cell surface receptors. Carbohydrate-derived inhibitors have been developed for cancer treatment. Intracellularly, Gal-1 was suggested to interact with the farnesylated C-terminus of Ras thus specifically stabilizing GTP-H-ras nanoscale signalling hubs in the membrane, termed nanoclusters. The latter activity may present an alternative mechanism for how overexpressed Gal-1 stimulates tumourigenesis. Here we revise the current model for the interaction of Gal-1 with H-ras. We show that it indirectly forms a complex with GTP-H-ras via a high-affinity interaction with the Ras binding domain (RBD) of Ras effectors. A computationally generated model of the Gal-1/C-Raf-RBD complex is validated by mutational analysis. Both cellular FRET as well as proximity ligation assay experiments confirm interaction of Gal-1 with Raf proteins in mammalian cells. Consistently, interference with H-rasG12V-effector interactions basically abolishes H-ras nanoclustering. In addition, an intact dimer interface of Gal-1 is required for it to positively regulate H-rasG12V nanoclustering, but negatively K-rasG12V nanoclustering. Our findings suggest stacked dimers of H-ras, Raf and Gal-1 as building blocks of GTP-H-ras-nanocluster at high Gal-1 levels. Based on our results the Gal-1/effector interface represents a potential drug target site in diseases with aberrant Ras signalling.

Galectin-1 inhibitors and their potential therapeutic applications: a patent review

INTRODUCTION

Galectins have affinity for β-galactosides. Human galectin-1 is ubiquitously expressed in the body and its expression level can be a marker in disease. Targeted inhibition of galectin-1 gives potential for treatment of inflammatory disorders and anti-cancer therapeutics.

AREAS COVERED

This review discusses progress in galectin-1 inhibitor discovery and development. Patent applications pertaining to galectin-1 inhibitors are categorised as monovalent- and multivalent-carbohydrate-based inhibitors, peptides- and peptidomimetics. Furthermore, the potential of galectin-1 protein as a therapeutic is discussed along with consideration of the unique challenges that galectin-1 presents, including its monomer-dimer equilibrium and oxidized and reduced forms, with regard to delivering an intact protein to a pathologically relevant site.

EXPERT OPINION

Significant evidence implicates galectin-1's involvement in cancer progression, inflammation, and host-pathogen interactions. Conserved sequence similarity of the carbohydrate-binding sites of different galectins makes design of specific antagonists (blocking agents/inhibitors of function) difficult. Key challenges pertaining to the therapeutic use of galectin-1 are its monomer-dimer equilibrium, its redox state, and delivery of intact galectin-1 to the desired site. Developing modified forms of galectin-1 has resulted in increased stability and functional potency. Gene and protein therapy approaches that deliver the protein toward the target are under exploration as is exploitation of different inhibitor scaffolds.

Molecular characterization of a novel proto-type antimicrobial protein galectin-1 from striped murrel

In this study, we reported a molecular characterization of a novel proto-type galectin-1 from the striped murrel Channa striatus (named as CsGal-1). The full length CsGal-1 was identified from an established striped murrel cDNA library and further we confirmed the sequence by cloning. The complete cDNA sequence of CsGal-1 is 590 base pairs (bp) in length and its coding region encoded a poly peptide of 135 amino acids. The polypeptide contains a galactoside binding lectin domain at 4-135. The domain carries a sugar binding site at 45-74 along with its signatures (H(45)-X-Asn(47)-X-Arg(49) and Trp(69)-X-X-Glu(72)-X-Arg(74)). CsGal-1 shares a highly conserved carbohydrate recognition domain (CRD) with galectin-1 from other proto-type galectin of teleosts. The mRNA expressions of CsGal-1 in healthy and various immune stimulants including Aphanomyces invadans, Aeromonas hydrophila, Escherchia coli lipopolysaccharide and poly I:C injected tissues of C. striatus were examined using qRT-PCR. CsGal-1 mRNA is highly expressed in kidney and is up-regulated with different immune stimulants at various time points. To understand its biological activity, the coding region of CsGal-1 gene was expressed in an E. coli BL21 (DE3) cloning system and its recombinant protein was purified. The recombinant CsGal-1 protein was agglutinated with mouse erythrocytes at a concentration of 4μg/mL in a calcium independent manner. CsGal-1 activity was inhibited by d-galactose at 25mM(-1) and d-glucose and d-fructose at 100mM(-1). The results of microbial binding assay showed that the recombinant CsGal-1 protein agglutinated only with the Gram-negative bacteria. Interestingly, we observed no agglutination against Gram-positive bacteria. Overall, the study showed that CsGal-1 is an important immune gene involved in the recognition and elimination of pathogens in C. striatus.

A guide into glycosciences: How chemistry, biochemistry and biology cooperate to crack the sugar code

BACKGROUND

The most demanding challenge in research on molecular aspects within the flow of biological information is posed by the complex carbohydrates (glycan part of cellular glycoconjugates). How the 'message' encoded in carbohydrate 'letters' is 'read' and 'translated' can only be unraveled by interdisciplinary efforts.

SCOPE OF REVIEW

This review provides a didactic step-by-step survey of the concept of the sugar code and the way strategic combination of experimental approaches characterizes structure-function relationships, with resources for teaching.

MAJOR CONCLUSIONS

The unsurpassed coding capacity of glycans is an ideal platform for generating a broad range of molecular 'messages'. Structural and functional analyses of complex carbohydrates have been made possible by advances in chemical synthesis, rendering production of oligosaccharides, glycoclusters and neoglycoconjugates possible. This availability facilitates to test the glycans as ligands for natural sugar receptors (lectins). Their interaction is a means to turn sugar-encoded information into cellular effects. Glycan/lectin structures and their spatial modes of presentation underlie the exquisite specificity of the endogenous lectins in counterreceptor selection, that is, to home in on certain cellular glycoproteins or glycolipids.

GENERAL SIGNIFICANCE

Understanding how sugar-encoded 'messages' are 'read' and 'translated' by lectins provides insights into fundamental mechanisms of life, with potential for medical applications.

Structural basis of redox-dependent modulation of galectin-1 dynamics and function

Galectin-1 (Gal-1), a member of a family of multifunctional lectins, plays key roles in diverse biological processes including cell signaling, immunomodulation, neuroprotection and angiogenesis. The presence of an unusual number of six cysteine residues within Gal-1 sequence prompted a detailed analysis of the impact of the redox environment on the functional activity of this lectin. We examined the role of each cysteine residue in the structure and function of Gal-1 using both experimental and computational approaches. Our results show that: (i) only three cysteine residues present in each carbohydrate recognition domain (CRD) (Cys2, Cys16 and Cys88) were important in protein oxidation, (ii) oxidation promoted the formation of the Cys16-Cys88 disulfide bond, as well as multimers through Cys2, (iii) the oxidized protein did not bind to lactose, probably due to poor interactions with Arg48 and Glu71, (iv) in vitro oxidation by air was completely reversible and (v) oxidation by hydrogen peroxide was relatively slow (1.7 ± 0.2 M(-1) s(-1) at pH 7.4 and 25°C). Finally, an analysis of key cysteines in other human galectins is also provided in order to predict their behaviour in response to redox variations. Collectively, our data provide new insights into the structural basis of Gal-1 redox regulation with critical implications in physiology and pathology.

Disaccharide binding to galectin-1: free energy calculations and molecular recognition mechanism

Galectin-1, a member of the conserved family of carbohydrate-binding proteins with affinity for β-galactosides, is a key modulator of diverse cell functions such as immune response and regulation. The binding affinity and specificity of galectin-1 for eight different β-galactosyl terminal disaccharides was studied using molecular-dynamics simulations in which the ligand was pulled away from the binding site using a mechanical force. We present what we believe to be a novel procedure, based on combinations of multistep trajectories, that was used to estimate the binding free energy (ΔG) of each disaccharide. The computed binding free energy differences show excellent correlation with experimental values determined previously. The small differences in affinity among the disaccharides are the result of an exquisite balance between the strengths of the galectin-sugar H-bonds and the H-bonds the protein and the disaccharides make with the solvent. Analysis of the free energies along the reaction coordinate shows that disaccharide unbinding/binding presents no energetic barrier and, therefore, is diffusion-limited. In addition, the calculations revealed that as the ligand is undocked from the binding site, breaking of protein-disaccharide H-bonds takes place in stages with intermediate states in which the interactions are bridged by water molecules.

Lactose binding to galectin-1 modulates structural dynamics, increases conformational entropy, and occurs with apparent negative cooperativity

Galectins are a family of lectins with a conserved carbohydrate recognition domain that interacts with beta-galactosides. By binding cell surface glycoconjugates, galectin-1 (gal-1) is involved in cell adhesion and migration processes and is an important regulator of tumor angiogenesis. Here, we used heteronuclear NMR spectroscopy and molecular modeling to investigate lactose binding to gal-1 and to derive solution NMR structures of gal-1 in the lactose-bound and unbound states. Structure analysis shows that the beta-strands and loops around the lactose binding site, which are more open and dynamic in the unbound state, fold in around the bound lactose molecule, dampening internal motions at that site and increasing motions elsewhere throughout the protein to contribute entropically to the binding free energy. CD data support the view of an overall more open structure in the lactose-bound state. Analysis of heteronuclear single quantum coherence titration binding data indicates that lactose binds the two carbohydrate recognition domains of the gal-1 dimer with negative cooperativity, in that the first lactose molecule binds more strongly (K(1)=21+/-6 x 10(3) M(-1)) than the second (K(2)=4+/-2 x 10(3) M(-1)). Isothermal calorimetry data fit using a sequential binding model present a similar picture, yielding K(1)=20+/-10 x 10(3) M(-1) and K(2)=1.67+/-0.07 x 10(3) M(-1). Molecular dynamics simulations provide insight into structural dynamics of the half-loaded lactose state and, together with NMR data, suggest that lactose binding at one site transmits a signal through the beta-sandwich and loops to the second binding site. Overall, our results provide new insight into gal-1 structure-function relationships and to protein-carbohydrate interactions in general.

Computational studies of human galectin-1: role of conserved tryptophan residue in stacking interaction with carbohydrate ligands

Galectins belong to the family of glycan-binding proteins, defined by at least one conserved carbohydrate-recognition domain with a highly conserved amino acid sequence and affinity for beta galactosides. They all possess a tryptophan residue in the carbohydrate binding site that forms hydrophobic contacts with the carbohydrate ligands. Site directed mutagenesis experiments have shown that this conserved aromatic residue plays a key role in the interaction. We have studied the interaction between the corresponding human Galectin-1 in silico mutants and different carbohydrate ligands using molecular dynamics in explicit solvent. The results confirm the importance of the conserved tryptophan residue in the affinity of the ligand and gives further insights into the mode of interaction between lactose derivatives and human Galectin-1.

Identification of a second, non-conserved amino acid that contributes to the unique sugar binding properties of the nematode galectin LEC-1

The basic disaccharide structure recognized by galectin family members is the lactosamine-like structure Galbeta1-4(3)Glc(NAc). The 32-kDa galectin LEC-1 of the nematode Caenorhabditis elegans is composed of two domains, each of which is homologous to vertebrate 14-kDa-type galectins. The N-terminal lectin domain of LEC-1 recognizes blood group A saccharide (GalNAcalpha1-3(Fucalpha1-2)Galbeta1-3GlcNAc), whereas this saccharide is poorly recognized by the C-terminal domain. Using a combination of site-directed mutagenesis and analysis of the sugar-binding profile by frontal affinity chromatography, we previously found that Thr41 in the N-terminal lectin domain of LEC-1 is important for its affinity for A-hexasaccharide. Thr41 is located on beta-strand S3, next to the three beta-strands S4-S6, where the conserved amino acids form the binding site for the basic Galbeta1-4(3)Glc(NAc) structure. Here, we report that a second amino acid, Asp133, in the N-terminal lectin domain of LEC-1, located on the beta-strand S2 adjacent to that containing Thr41, is important for LEC-1-specific recognition of A-hexasaccharide. These results suggest that amino acid residues other than those located on the three beta-strands S4-S6, contribute to the unique sugar binding specificity of individual galectins.

Identification of the amino acid residue in the nematode galectin LEC-1 responsible for its unique sugar binding property: analysis by combination of site-directed mutagenesis and frontal affinity chromatography

The basic disaccharide structure recognized by galectin family members is the lactosamine-like structure Galbeta1-4(3)Glc(NAc). In galectins, eight highly conserved amino acid residues participate in the recognition of this basic structure. Each galectin seems to mediate diverse biological functions due to recognition of different modifications of the basic disaccharide Galbeta1-4(3)Glc(NAc), but there is very little information about which amino acid residue in galectin is responsible for recognizing these modifications. The 32-kDa galectin LEC-1 of the nematode Caenorhabditis elegans is composed of two domains, each of which is homologous to vertebrate 14-kDa-type galectins. Although both lectin domains have an affinity for N-acetyllactosamine (Galbeta1-4GlcNAc)-containing, N-linked, complex-type sugar chains, the N-terminal lectin domain of LEC-1 recognizes blood group A saccharide (GalNAcalpha1-3(Fucalpha1-2)Galbeta1-3GlcNAc), whereas this saccharide is only poorly recognized by the C-terminal domain. Here, we used a combination of site-directed mutagenesis of the N-terminal lectin domain of galectin LEC-1 and an analysis of the sugar-binding profile by frontal affinity chromatography to identify the amino acid residues important for this recognition. Our results indicate that Thr(41) in the N-terminal lectin domain of LEC-1 is important for its affinity for A-hexasaccharide.

Characterization of the Interaction of Galectin-1 with Sodium Arsenite

We previously showed that galectin-1 (GAL1) is an arsenic-binding protein. In the current study, we further characterize the interaction of GAL1 with sodium arsenite (As(III)). The GALl-As(III) complex was prepared from the cell extracts of GAL1-transfected Escherichia coli (E. coli) that were pretreated with As(III). The results of the circular dichroism (CD) spectrum of GAL1-As(III) exhibited a negative signal at around 205-210 nm, whereas that of GAL1 showed a negative signal at around 215-220 nm. This shift in the CD spectrum is indicative of a substantial change in the secondary structure arising from the binding of As(III) to the GAL1 protein. The UV absorptive spectrum of the GAL1-As(III) complex was significantly lower than that of GAL1 itself. A mobility shift binding assay showed that the GAL1-As(III) complex migrated closer than GAL1 toward the anode. Capillary electrophoretic analysis also showed that As(III) binding decreased the mobility of GAL1. These results further confirmed the structural change of the GAL1 complex with As(III). Furthermore, isothermal titration microcalometric studies showed that As(III) titration into the GAL1 protein solution was an endothermic process with absorption enthalpy (DeltaH(abs)) around 8-10 kJ/mol As(III). The affinity constant (K(d)) of As(III) toward GAL1 was around 8.239 +/- 2.627 microM as estimated by tryptophan (Trp) fluorescence quenching. However, the binding of As(III) did not significantly affect the biological activity of GAL1, since the GAL1-As(III) complex only partially lost its lectin activity. In addition, we show that GAL1-transfected KB cells accumulated more arsenic than did the parental cells. Taken together, these results suggest that GAL1 might serve as a target protein of As(III) in vivo, and the binding of GAL1 with As(III) could interfere with the excretion of As(III).

Oligosaccharide specificity of galectins: a search by frontal affinity chromatography

Galectins are widely distributed sugar-binding proteins whose basic specificity for beta-galactosides is conserved by evolutionarily preserved carbohydrate-recognition domains (CRDs). Although they have long been believed to be involved in diverse biological phenomena critical for multicellular organisms, in only few a cases has it been proved that their in vivo functions are actually based on specific recognition of the complex carbohydrates expressed on cell surfaces. To obtain clues to understand the physiological roles of diverse members of the galectin family, detailed analysis of their sugar-binding specificity is necessary from a comparative viewpoint. For this purpose, we recently reinforced a conventional system for frontal affinity chromatography (FAC) [J. Chromatogr., B, Biomed. Sci. Appl. 771 (2002) 67-87]. By using this system, we quantitatively analyzed the interactions at 20 degrees C between 13 galectins including 16 CRDs originating from mammals, chick, nematode, sponge, and mushroom, with 41 pyridylaminated (PA) oligosaccharides. As a result, it was confirmed that galectins require three OH groups of N-acetyllactosamine, as had previously been denoted, i.e., 4-OH and 6-OH of Gal, and 3-OH of GlcNAc. As a matter of fact, no galectin could bind to glycolipid-type glycans (e.g., GM2, GA2, Gb3), complex-type N-glycans, of which both 6-OH groups are sialylated, nor Le-related antigens (e.g., Le(x), Le(a)). On the other hand, considerable diversity was observed for individual galectins in binding specificity in terms of (1) branching of N-glycans, (2) repeating of N-acetyllactosamine units, or (3) substitutions at 2-OH or 3-OH groups of nonreducing terminal Gal. Although most galectins showed moderately enhanced affinity for branched N-glycans or repeated N-acetyllactosamines, some of them had extremely enhanced affinity for either of these multivalent glycans. Some galectins also showed particular preference for alpha1-2Fuc-, alpha1-3Gal-, alpha1-3GalNAc-, or alpha2-3NeuAc-modified glycans. To summarize, galectins have evolved their sugar-binding specificity by enhancing affinity to either "branched", "repeated", or "substituted" glycans, while conserving their ability to recognize basic disaccharide units, Galbeta1-3/4GlcNAc. On these bases, they are considered to exert specialized functions in diverse biological phenomena, which may include formation of local cell-surface microdomains (raft) by sorting glycoconjugate members for each cell type.

Cloning and expression of a novel human galectin cDNA, predominantly expressed in placenta(1)

A novel human galectin cDNA (PPL13) was isolated by screening a human 18-week fetal brain library. The mRNA was predominantly expressed in placenta, while the expression of it was not or barely detectable in heart, brain, lung, liver, skeletal muscle, kidney, and pancreas by Northern blot. COS-7 cells transfected with cDNA encoding human PPL13 sequestered the protein in nuclei although it lacked any known nuclear localization signal. STS of Unigene Hs. 24236 placed the cDNA to human chromosome 19q13.2.

Identification of oxidized galectin-1 as an initial repair regulatory factor after axotomy in peripheral nerves

Various neurotrophic factors that promote axonal regeneration have been investigated in vivo, but the signals that prompt the axons to send out processes in peripheral nerves after axotomy are not well understood. We have shown using two specific strategies that galectin-1 can play an important role in this initial stage. One used an in vitro nerve regeneration model that allowed us to monitor the initial axon and support cell outgrowth from the proximal nerve stump comparable to the initial stages of nerve repair. The other strategy was to clarify the axonal regeneration-promoting factor from kidney-derived cells. Using these strategies, we discovered that oxidized galectin-1 from the cell (COS1 cell) conditioned media acts as an axonal regeneration-promoting factor without the lectin activity. Oxidized recombinant human galectin-1 (rhGAL-1/Ox) showed the same activity at low concentrations (pg/ml range). A similarly low concentration also effectively promoted axonal regeneration in both transection and crush experiments in vivo. Moreover, the application of functional anti-galectin-1 antibody strongly inhibited the regeneration in vivo. Since galectin-1was shown to be secreted and localized in the regenerating sciatic nerve, this suggests that secreted galectin-1 may be oxidized and change its molecular structure to regulate initial repair after axotomy as a kind of cytokine.

Role of sarcolectin (SCL) and interferons in coordinated T cell clonal expansion

T cell multiplication is attributed to the growth factor interleukin-2 (IL-2), which is, however, only activated when a specific cell membrane-bound receptor can be expressed. We found in all human sera tested a lectin that we described and called sarcolectin (SCL). SCL is a molecularly cloned 55-kDa protein that stimulates DNA synthesis in all immunocompetent cells and inhibits the interferon (IFN)-dependent antiviral state. SCL is excreted in conditioned medium of T cell cultures grown under serum-free conditions, where it can be demonstrated regularly by Western blots. In such cultures, in addition to SCL and IL-2, IFN-gamma and IFN-alpha also can be found, likely as a feedback response to DNA stimulation. Considered together, the data suggest that coordinated clonal expansion of T cells is governed by SCL-IL-2, both which induce T cell proliferation and simultaneously activate IL-2 receptors. T cell replication is downregulated by the effect of feedback IFN-gamma and IFN-alpha. To initiate a new growth cycle, SCL is thought to block the residual IFN-dependent antiproliferative state.

Oxidized galectin-1 promotes axonal regeneration in peripheral nerves but does not possess lectin properties

Galectin-1 has recently been identified as a factor that regulates initial axonal growth in peripheral nerves after axotomy. Although galectin-1 is a well-known beta-galactoside-binding lectin, its potential to promote axonal regeneration as a lectin has not been reported. It is essential that the process of initial repair in peripheral nerves after axotomy is well clarified. We therefore undertook to investigate the relation between the structure and axonal regeneration-promoting activity of galectin-1. Recombinant human galectin-1 secreted into the culture supernatant of transfected COS1 cells (rhGAL-1/COS1) was purified under nonreducing conditions and subjected to structural analysis. Mass spectrometric analysis of peptide fragments from rhGAL-1/COS1 revealed that the secreted protein exists as an oxidized form containing three intramolecular disulfide bonds (Cys2-Cys130, Cys16-Cys88 and Cys42-Cys60). Recombinant human galectin-1 (rhGAL-1) and a galectin-1 mutant in which all six cysteine residues were replaced by serine (CSGAL-1) were expressed in and purified from Escherichia coli for further analysis; the purified rhGAL-1 was subjected to oxidation, which induced the same pattern of disulfide linkages as that observed in rhGAL-1/COS1. Oxidized rhGAL-1 enhanced axonal regeneration from the transected nerve sites of adult rat dorsal root ganglion explants with associated nerve stumps (5.0-5000 pg. mL-1), but it lacked lectin activity. In contrast, CSGAL-1 induced hemagglutination of rabbit erythrocytes but lacked axonal regeneration-promoting activity. These results indicate that galectin-1 promotes axonal regeneration only in the oxidized form containing three intramolecular disulfide bonds, not in the reduced form which exhibits lectin activity.

Functional and structural characterization of multiple galectins from the skin mucus of conger eel, Conger myriaster

The complete amino acid sequence of an isogalectin, named congerin II, isolated from the skin mucus of conger eel, was determined by sequencing of the protein and its peptides generated by enzymatic and chemical cleavages. Congerin II consisted of 135 amino acids residues containing an acetylated N-terminus. Congerin II was found to be only 46% homologous in sequence to congerin I which was previously determined (Muramoto K., Kamiya H., Biochem. Biophys. Acta, 1992;1116:129-136), suggesting that the galectins with diverse molecular properties are present in the skin mucus of conger eel. However, it was confirmed by analysis of the secondary structures using circular dichroism that both congerins I and II shared similar folds characterized by beta structures. Congerins I and II showed different molecular properties such as thermostability, pH dependency for hemagglutinating activity and for binding specificity against the pyridylamino derivative of lactose. Congerin I showed more strict recognition specificity for lactose than did congerin II. Furthermore, the effects of chemical modification on congerins I and II were investigated in order to identify the type of amino acids involved in their different lectin activities. Modification of tyrosine and lysine residues did not affect the carbohydrate-binding activities of congerins. However, modification of tryptophan, arginine, histidine, glutamic acid and aspartic acid residues led to considerable loss of their activities, and a different mode of binding activity was observed between modified congerins I and II. These results suggest that multiple galectins from conger eel with the same scaffold have different biological functions and properties.

Structural basis for the recognition of carbohydrates by human galectin-7

Knowledge about carbohydrate recognition domains of galectins, formerly known as S-type animal lectins, is important in understanding their role(s) in cell-cell interactions. Here we report the crystal structure of human galectin-7 (hGal-7), in free form and in the presence of galactose, galactosamine, lactose, and N-acetyl-lactosamine at high resolution. This is the first structure of a galectin determined in both free and carbohydrate-bound forms. The structure shows a fold similar to that of the prototype galectins -1 and -2, but has greater similarity to a related galectin molecule, Gal-10. Even though the carbohydrate-binding residues are conserved, there are significant changes in this pocket due to shortening of a loop structure. The monomeric hGal-7 molecule exists as a dimer in the crystals, but adopts a packing arrangement considerably different from that of Gal-1 and Gal-2, which has implications for carbohydrate recognition.

Evidence for subsites in the galectins involved in sugar binding at the nonreducing end of the central galactose of oligosaccharide ligands: sequence analysis, homology modeling and mutagenesis studies of hamster galectin-3

A model of the carbohydrate recognition domain CRD, residues 111-245, of hamster galectin-3 has been made using homology modeling and dynamics minimization methods. The model is based on the known x-ray structures of bovine galectin-1 and human galectin-2. The oligosaccharides NeuNAc-alpha2,3-Gal-beta1,4-Glc and GalNAc-alpha1, 3-[Fuc-alpha1,2]-Gal-beta1,4-Glc, known to be specific high-affinity ligands for galectin-3, as well as lactose recognized by all galectins were docked in the galectin-3 CRD model structure and a minimized binding conformation found in each case. These studies indicate a putative extended carbohydrate-binding subsite in the hamster galectin-3 involving Arg139, Glu230, and Ser232 for NeuNAc-alpha2,3-; Arg139 and Glu160 for fucose-alpha1,2-; and Arg139 and Ile141 for GalNAc-alpha1,3- substituents on the primary galactose. Each of these positions is variable within the whole galectin family. Two of these residues, Arg139 and Ser232, were selected for mutagenesis to probe their importance in this newly identified putative subsite. Residue 139 adopts main-chain dihedral angles characteristic of an isolated bridge structural feature, while residue 232 is the C-terminal residue of beta-strand-11, and is followed immediately by an inverse gamma-turn. A systematic series of mutant proteins have been prepared to represent the residue variation present in the aligned sequences of galectins-1, -2, and -3. Minimized docked models were generated for each mutant in complex with NeuNAc-alpha2,3-Gal-beta1,4-Glc, GalNAc-alpha1, 3-[Fuc-alpha1,2]-Gal-beta1,4- Glc, and Gal-beta1,4-Glc. Correlation of the computed protein-carbohydrate interaction energies for each lectin-oligosaccharide pair with the experimentally determined binding affinities for fetuin and asialofetuin or the relative potencies of lactose and sialyllactose in inhibiting binding to asiolofetuin is consistent with the postulated key importance of Arg139 in recognition of the extended sialylated ligand.

Involvement of laser photo-CIDNP (chemically induced dynamic nuclear polarization)-reactive amino acid side chains in ligand binding by galactoside-specific lectins in solution

For proteins in solution the validity of certain crystallographic parameters can be ascertained by a combination of molecular-dynamics (MD) simulations and NMR spectroscopy. Using the laser photo-CIDNP (chemically induced dynamic nuclear polarization) technique as a measure for surface accessibility of histidine, tyrosine and tryptophan, the spectra of bovine galectin-1 and Erythrina corallodendron lectin (EcorL) are readily reconcilable with the crystallographic data for these two proteins. The results emphasise the role of Trp68/Trp69 for carbohydrate binding in bovine galectin-1/chicken galectins and of Trp194 in murine galectin-3. This feature derived from the crystal structure of bovine galectin-1 is maintained in solution for the prototype human homologue, two avian galectins and the chimera-type murine galectin-3, as the spectra corroborate the CIDNP-inferable spatial parameters of the four calculated models for binding-site architecture. In EcorL, Tyr106/Tyr108 are constituents of the extended combining pocket, which can be shielded in solution by ligand presence. Discrepancies between results from modelling and CIDNP measurements concern primarily the lack of reactivity of histidine residues for human and avian prototype galectins and of Tyr82/Tyr229 of the plant lectin. Site-directed mutagenesis of EcorL is assumed to provide information on the role of a certain residue for functional aspects. When single-site mutants of EcorL ([Ala106]EcorL, [Ala108]EcorL, [Ala229]EcorL) were subjected to molecular-dynamics (MD) simulations, the apparent surface accessibilities even of spatially separated amino acid side chains could non-uniformly be affected. This conclusion is supported by the assessment of the spectra for the mutant proteins. On the basis of these CIDNP-results modelling of the binding-site architecture of the lectin indicates the occurrence of notable alterations in the orientation of Tyr106/Tyr108 phenyl rings. The implied potential effect of single-site mutations on conformational features of a protein will deserve attention for the interpretation of studies comparing wild-type and mutant proteins.

Thermodynamics of carbohydrate binding to galectin-1 from Chinese hamster ovary cells and two mutants. A comparison with four galactose-specific plant lectins

The thermodynamics of carbohydrate binding to the 14 kDa dimeric beta-galactoside-binding lectin galectin-1 (Gal-1) from Chinese hamster ovary cells and four galactose-specific plant lectins were investigated by isothermal titration microcalorimetry. Recombinant Gal-1 from Escherichia coli, a Cys-->Ser mutant with enhanced stability (C2S-Gal-1), and a monomeric mutant of the lectin (N-Gal-1) were studied along with the soybean agglutinin and the lectins from Erythrina indica, Erythrina crystagalli, and Erythrina corollodendrum. Although the pattern of association constants of the Erythrina lectins was similar for mono- and disaccharides, variations exist in their enthalpy of binding (-delta H) values for individual carbohydrates. While the Erythrina lectins show greater affinities and -delta H values for lactose and N-acetyllactosamine, the soybean agglutinin possesses similar affinities for methyl beta-galactopyranoside, lactose, and N-acetyllactosamine and a greater -delta H value for the monosaccharide. Gal-1 and the plant lectins possess essentially the same affinities for N-acetyllactosamine; however, the animal lectin shows a lower -delta H value and more favorable binding entropy for the disaccharide. While Gal-1, C2S-Gal-1, and N-Gal-1 all possess essentially the same affinities for N-acetyllactosamine, the two mutants possess much lower -delta H values, even though the mutation site(s) are far removed from the carbohydrate binding site. These results indicate that there are different energetic mechanisms of carbohydrate binding between galectin-1, its two mutants, and the Gal-specific plant lectins.

Characterization of monomeric forms of galectin-1 generated by site-directed mutagenesis

Galectin-1 is a beta-galactoside-binding protein secreted by animal cells, and it exists in a monomer-dimer equilibrium (Kd approximately 7 microM). The function(s) of galectin-1 is(are) not yet defined, but dimerization and divalency are presumably important. Crystal structures of the mammalian galectin-1 dimer predict N- and C-terminal interactions at the subunit interface. To examine the mechanism of dimer formation and possibly generate active monomeric galectin-I, mutations were made in the N- and C-termini of recombinant hamster galectin-1. N-Gal-1 contains disruptions of three hydrophobic amino acids at the N-terminus; V5D-Gal-1 contains a single mutation of Val5 to Asp; N/C-Gal-1 contains multiple changes in hydrophobic amino acids at both the N- and C-termini. All mutants behave as monomers in size-exclusion HPLC and native gel electrophoresis. N-Gal-1 and V5D-Gal-1 bind weakly to lactosyl-Sepharose, but N/C-Gal-1 is nonfunctional. In equilibrium dialysis, N-Gal-1 and V5D-Gal-1 bind N-acetyllactosamine with a Kd approximately 90 microM, which is similar to that of native lectin. At high concentrations, V5D-Gal-1 and N-Gal-1 dimerize and can be covalently cross-linked with disuccinimidyl suberate. The Kd values of the monomer-dimer equilibrium for V5D-Gal-1 and N-Gal-1 are estimated to be approximately 60 microM and approximately 250 microM, respectively. The cross-linked dimers of V5D and N-Gal-1 were isolated and were similar to native lectin in both hemagglutinating activity and high-affinity binding to lactosyl-Sepharose. Thus, specific mutations in galectin-1 can alter monomer-dimer equilibrium without affecting carbohydrate-binding activity. The availability of active monomers and functional covalent dimers of galectin-1 should aid in future studies aimed at understanding the biological function(s) of the lectin and the role of divalency.

Biphasic modulation of cell growth by recombinant human galectin-1

Human soluble galactose-binding lectin (galectin-1) has been expressed as an Escherichia coli fusion protein, following the amplification by polymerase chain reaction of cDNA prepared from a human osteosarcoma cell line. The fusion protein is a functional beta-galactoside-binding lectin, as is the recombinant galectin when purified from the cleaved fusion protein. The recombinant galectin has a biphasic effect on cell proliferation. Unlike the fusion protein, it functions as a human cell growth inhibitor, confirming earlier findings with natural human galectin-1, though it is less effective than the natural galectin. This reaction is not significantly inhibited by lactose, and is thus largely independent of the beta-galactoside-binding site. At lower concentrations, recombinant galectin-1 is mitogenic, this activity being susceptible to inhibition by lactose, and thus attributable to the beta-galactoside-binding ability of the protein. Some tumour cells are susceptible to the growth-inhibitory effect, and the galectin-1 gene is expressed in both normal and tumour cells.

Crystal structure of human Charcot-Leyden crystal protein, an eosinophil lysophospholipase, identifies it as a new member of the carbohydrate-binding family of galectins

BACKGROUND

The Charcot-Leyden crystal (CLC) protein is a major autocrystallizing constituent of human eosinophils and basophils, comprising approximately 10% of the total cellular protein in these granulocytes. Identification of the distinctive hexagonal bipyramidal crystals of CLC protein in body fluids and secretions has long been considered a hallmark of eosinophil-associated allergic inflammation. Although CLC protein possesses lysophospholipase activity, its role(s) in eosinophil or basophil function or associated inflammatory responses has remained speculative.

RESULTS

The crystal structure of the CLC protein has been determined at 1.8 A resolution using X-ray crystallography. The overall structural fold of CLC protein is highly similar to that of galectins -1 and -2, members of an animal lectin family formerly classified as S-type or S-Lac (soluble lactose-binding) lectins. This is the first structure of an eosinophil protein to be determined and the highest resolution structure so far determined for any member of the galectin family.

CONCLUSIONS

The CLC protein structure possesses a carbohydrate-recognition domain comprising most, but not all, of the carbohydrate-binding residues that are conserved among the galectins. The protein exhibits specific (albeit weak) carbohydrate-binding activity for simple saccharides including N-acetyl-D-glucosamine and lactose. Despite CLC protein having no significant sequence or structural similarities to other lysophospholipase catalytic triad has also been identified within the CLC structure, making it a unique dual-function polypeptide. These structural findings suggest a potential intracellular and/or extracellular role(s) for the galectin-associated activities of CLC protein in eosinophil and basophil function in allergic diseases and inflammation.

Galectin-1, a beta-galactoside-binding lectin in Chinese hamster ovary cells. I. Physical and chemical characterization

We report our studies on the characterization of an approximately 14-kDa lectin, termed galectin-1 that we have found to be expressed by Chinese hamster ovary (CHO) cells. cDNA for galectin-1 from CHO cells was prepared and sequenced, and a recombinant form (rGal-1) was expressed in Escherichia coli. A mutated form of the protein that fully retained activity was also constructed (termed C2SrGal-1) in which Cys-2 was changed to Ser-2. rGal-1 was stable in the presence of reducing agent, but it quickly lost all activity in the absence of reducing agent. In contrast, glycoprotein ligands, such as basement membrane laminin, stabilized the activity of rGal-1 in the absence of reducing agent (t1/2 = 2 weeks). C2SrGal-1 was stable in the presence or absence of either ligand or reducing agent. Unexpectedly, galectin-1 was found to exist in a reversible and active monomer-dimer equilibrium with a Kd approximately 7 microM and an equilibration time of t1/2 approximately 10 h. Addition of haptenic sugars did not affect this equilibrium. Galectin-1 isolated from the cytosol of CHO cells was found to exist as monomers and dimers. These studies demonstrate that galectin-1 binding to a biological ligand stabilizes its activity and that the monomer/dimer state of the protein is regulated by lectin concentration.

Purification and characterization of natural antibodies that recognize a human brain lectin

We have recently identified oligoclonal IgG antibodies that are related to a human brain lectin (HBL14) from serum and cerebrospinal fluid of patients with neurological disorders. They were termed lectin-like IgG (L-IgG) (Joubert-Caron et al., 1994a,b). In this paper, the occurrence of antibodies reactive both towards HBL14 and L-IgG was investigated. Binding of antibodies to HBL14 was demonstrated by solid-phase ELISA and chromatography on immobilized HBL14. Fab fragments of these antibodies were also shown to bind to HBL14. The specificity of the antibodies towards HBL14 was studied using a panel of different antigens. Our data show that individual sera from healthy people as well as a pool of immunoglobulins from 80 blood donors contain an IgG autoreactivity to HBL14, while no IgM autoreactivity was detected. Anti-HBL14 antibodies from sera were purified using affinity chromatography on immobilized HBL14. Affinity chromatography further allowed us to demonstrate that the binding of anti-HB14 antibodies was mediated through their Fab fragments. A higher amount of anti-HBL14 antibodies was purified using a L-IgG-depleted fraction of sera. The binding of anti-HBL14 antibodies to L-IgG was confirmed by ELISA. Finally, anti-HBL14 antibodies were found to be polyreactive. These results indicate the occurrence of a novel class of natural antibodies reactive towards a human brain lectin and suggest that these antibodies may participate in immunoregulatory mechanisms probably though idiotypic/anti-idiotypic interaction.

Changes in expression of two endogenous beta-galactoside-binding isolectins in the dermis of chick embryonic skin during development in ovo and in vitro

In order to elucidate the roles of metal-independent animal lectins, we systematically investigated changes in expression of 2 kinds of beta-galactoside-binding isolectins (MW 14 and 16 kDa) in the dermis of chick embryonic tarsometatarsal skin during the course of development. These lectins were immunohistochemically located at different stages of development both in ovo and in vitro by light and electron microscopy. Light-microscopic observation showed that while positive staining for the 14-kDa lectin was weak at days 8 and 10 it became intense after day 13. In contrast, staining for the 16-kDa lectin was intense at days 8, 10, and 13, but it became weak after day 17 when keratinization of the epidermis was completed. Immuno-electron-microscopic observation revealed that both the 14 and 16-kDa lectins were located on the basement membrane, in the extracellular matrix, and in both the cytoplasm and the nucleus of dermal fibroblasts. Distribution of the 2 isolectins was also examined in cultured skin explants in vitro. The results were almost the same as those obtained in ovo when the skin explant was keratinized in the presence of hydrocortisone. However, in the skin explant where keratinization was prevented and mucous metaplasia was induced by the addition of vitamin A, the distribution of the 14-kDa lectin in the epidermis was significantly affected. These results indicate that (1) the expression of the 2 isolectins is differently regulated in both the dermis and epidermis, (2) the 16-kDa lectin is involved in the early stage of the formation of the dermis and the basement membrane and is replaced by the 14-kDa lectin as keratinization of the epidermis occurs, and (3) the expression of the 2 isolectins in the dermis is not significantly affected by the induction of mucous metaplasia, in contrast to their drastic changes in the epidermis.

Crosslinking of mammalian lectin (galectin-1) by complex biantennary saccharides

Galectins are beta-galactoside-binding proteins that occur intra- and extracellularly in many animal tissues. They have been proposed to form networks of glycoconjugates on the cell surface, where they may modulate various cell response pathways such as growth, activation and adhesion. The high resolution X-ray crystallographic analyses of three crystal forms of bovine galectin-1 in complex with biantennary saccharides of N-acetyllactosamine type reveal infinite chains of lectin dimers cross-linked through N-acetyllactosamine units located at the end of the oligosaccharide antenna. The oligosaccharide adopts a different low energy conformation in each of the three crystal forms.

Oligoclonal beta-galactoside-binding immunoglobulins antigenically related to 14 kDa lectin in human serum and cerebrospinal fluid: purification and characterization

1. An antiserum raised against a 14 kDa beta-galactoside specific lectin from human brain (HBL14) was used to probe blots from samples of serum and cerebrospinal fluid. The only HBL14-immunoreactive material detected was heavy and light chains of a beta-galactoside-binding IgG fraction (lectin-like IgG). 2. Lectin-like IgG, as well as IgG Fab fragments, compete with HBL14 for binding either to anti-HBL14 antibody or to a lactosyl polyacrylamide-based copolymer. 3. Purification of lectin-like IgG was obtained by affinity chromatography on immobilized rabbit anti-lectin immunoglobulins. The carbohydrate-binding specificity of the purified molecules was restricted to beta-Gal-containing structures and close to the HBL14 one.

The adhesive specificity of the soluble human lectin, IgE-binding protein, toward lipid-linked oligosaccharides. Presence of the blood group A, B, B-like, and H monosaccharides confers a binding activity to tetrasaccharide (lacto-N-tetraose and lacto-N-neotetraose) backbones

The immunoglobulin E-binding protein, epsilon BP (also known as CBP35, Mac-2, L-34, and L-29), is a beta-galactoside-binding protein of approximately 30 kDa and a member of the animal lectin family termed S-type or S-Lac. Multiple biological activities have been attributed to this lectin such as mediation of IgE binding to the surface of Langerhans cells and activation of mast cells through binding to the high affinity IgE receptor. In order to better understand the cell-binding activity and the proposed role for epsilon BP as a biological response modifier, we have studied the specificity of binding of the radioiodinated epsilon BP to a series of lipid-linked, structurally defined oligosaccharide sequences of the lacto/neolacto family. The results show that the minimum lipid-linked oligosaccharides that can support epsilon BP binding are pentasaccharides of the lacto/neolacto series and that the lectin binds more strongly to oligosaccharides of this family that bear the blood group A, B, or B-like determinants than to those bearing blood group H. This preferential binding of epsilon BP is also manifest with whole cells, as erythrocytes of blood groups A and B are more strongly bound by epsilon BP than those of blood group O. Blood group Le(a) and Le(x) sequences are not bound by the lectin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal lectins as self/non-self recognition molecules. Biochemical and genetic approaches to understanding their biological roles and evolution

In recent years, the significant contributions from molecular research studies on animal lectins have elucidated structural aspects and provided clues not only to their evolution but also to their multiple biological functions. The experimental evidence has suggested that distinct, and probably unrelated, groups of molecules are included under the term "lectin." Within the invertebrate taxa, major groups of lectins can be identified: One group would include lectins that show significant homology to membrane-integrated or soluble vertebrate C-type lectins. The second would include those beta-galactosyl-specific lectins homologous to the S-type vertebrate lectins. The third group would be constituted by lectins that show homology to vertebrate pentraxins that exhibit lectin-like properties, such as C-reactive protein and serum amyloid P. Finally, there are examples that do not exhibit similarities to any of the aforementioned categories. Moreover, the vast majority of invertebrate lectins described so far cannot yet be placed in one or another group because of the lack of information regarding their primary structure. (See Table 1.) Animal lectins do not express a recombinatorial diversity like that of antibodies, but a limited diversity in recognition capabilities would be accomplished by the occurrence of multiple lectins with distinct specificities, the presence of more than one binding site, specific for different carbohydrates in a single molecule, and by certain "flexibility" of the binding sites that would allow the recognition of a range of structurally related carbohydrates. In order to identify the lectins' "natural" ligands, we have investigated the interactions between those proteins and the putative endogenous or exogenous glycosylated substances or cells that may be relevant to their biological function. Results from these studies, together with information on the biochemical properties of invertebrate and vertebrate lectins, including their structural relationships with other vertebrate recognition molecules, are discussed.

Normal development of mice carrying a null mutation in the gene encoding the L14 S-type lectin

The L14 lectin is a 14 × 10(3) M(r) carbohydrate binding protein belonging to the family of S-type lectins. The pattern of expression of this protein during mouse embryogenesis suggests that it may have multiple roles during pre- and post-implantation development. Using the technique of homologous recombination in embryonic stem cells, we have introduced a null mutation in the gene encoding the L14 lectin and generated a strain of mice carrying the mutant allele. We report here that homozygous mutant animals that lack the L14 lectin develop normally and are viable and fertile. The absence of any major phenotypic abnormalities in these mutant animals suggests that other protein(s) potentially compensate for the absence of the L14 lectin. Here we show that a related protein termed L30, a lectin that has carbohydrate binding specificity similar to that of L14, is present in the same embryonic cell populations as L14 at the time of implantation, suggesting that the two S-type lectins may be capable of functional substitution at this early stage of embryogenesis.

S-type mammalian lectins in allergic inflammation

Our understanding of the mechanisms of allergic disease is continuously influenced by new developments in the bio-medical sciences. The studies of glycoconjugates and animal lectins have emerged as an exciting new frontier. One family of animal lectins, soluble lactose-binding lectins, has been studied extensively by a number of laboratories. Evidence is mounting that members of this family of lectins exist in the extracellular space and may be capable of affecting functions of various cells. In this article Fu-Tong Liu presents a revised view of allergic inflammation with emphasis on the modulatory effect of soluble lectins on mast-cell function.