A Review of the Leishmanicidal Properties of Lectins

Lectins are proteins widely distributed among plants, animals and microorganisms that have the ability to recognize and interact with specific carbohydrates. They have varied biological activities, such as the inhibition of the progression of infections caused by fungi, bacteria, viruses and protozoa, which is related to the interaction of these proteins with the carbohydrates present in the cell walls of these microorganisms. Leishmaniasis are a group of endemic infectious diseases caused by protozoa of the genus Leishmania. In vitro and in vivo tests with promastigotes and amastigotes of Leishmania demonstrated that lectins have the ability to interact with glycoconjugates present on the cell surface of the parasite, it prevents their development through various mechanisms of action, such as the production of ROS and alteration of membrane integrity, and can also interact with defense cells present in the human body, thus showing that these molecules can be considered alternative pharmacological targets for the treatment of leishmaniasis. The objective of the present work is to carry out a bibliographic review on lectins with leishmanicidal activity, emphasizing the advances and perspectives of research in this theme. Through the analysis of the selected studies, we were able to conclude that lectins have great potential for inhibiting the development of leishmaniasis. However, there are still few studies on this subject.

Dioclea violacea lectin increases the effect of neomycin against multidrug-resistant strains and promotes the purification of the antibiotic in immobilized lectin column

DVL is a Man/Glc-binding lectin from Dioclea violacea seeds that has the ability to interact with the antibiotic gentamicin. The present work aimed to evaluate whether the DVL has the ability to interact with neomycin via CRD and to examine the ability of this lectin to modulate the antibiotic effect of neomycin against multidrug-resistant strains (MDR). The hemagglutinating activity test revealed that neomycin inhibited the hemagglutinating activity of DVL with a minimum inhibitory concentration of 50 mM, indicating that the antibiotic interacts with DVL via the carbohydrate recognition domain (CRD). DVL immobilized on cyanogen bromide-activated Sepharose® 4B bound 41 % of the total neomycin applied to the column, indicating that the DVL-neomycin interaction is efficient for purification processes. Furthermore, the minimum inhibitory concentrations (MIC) obtained for DVL against all strains studied were not clinically relevant. However, when DVL was combined with neomycin, a significant increase in antibiotic activity was observed against S. aureus and P. aeruginosa. These results demonstrate the first report of lectin-neomycin interaction, indicating that immobilized DVL has the potential to isolate neomycin by affinity chromatography. Moreover, DVL increased the antibiotic activity of neomycin against MDR, suggesting that it is a potent adjuvant in the treatment of infectious diseases.

Molecular characterization, immune responses, and functional aspects of atypical prototype galectin from redlip mullet (Liza haematocheila) as a pattern recognition receptor in host immune defense system

Galectins are a family of lectins that are widely distributed β-galactoside-binding proteins identified in diverse organisms. Galectin family have appeared as pattern recognition receptors (PRRs) responsible for initiating and controlling the innate immunity. The present study aimed to study the binding ability and potential role in PRRs of galectin-related protein B-like (LhGal B-like) from redlip mullet (Liza haematocheila) involved in the host immune responses. We constructed a cDNA library of redlip mullet and identified the LhGal B-like sequence. By sequence analysis and multiple sequence alignment, we revealed that LhGal B-like contains a conserved carbohydrate recognition domain (CRD) and consists of 135 amino acids with a predicted molecular weight of 16.07 kDa. In addition, pairwise comparison results showed that LhGal B-like shares higher sequence identity (82.2-95.2%) and similarity (89-95.9%) with fish species than those (34.1-37.8% and 57.2-58.1%, respectively) with other species. The phylogenetic tree showed that LhGal B-like clustered into the fish group and was evolutionally related to Mastacembelus armatus. The tissue distribution results revealed that LhGal B-like was expressed ubiquitously in all the tested tissues, where it was highly expressed in the brain, followed by gills and muscle. The immune modulated expression of LhGal B-like was observed by injecting lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (poly I:C) and Lactococcus garvieae (L. garvieae). According to the results, in the gills, the mRNA expression of LhGal B-like was significantly upregulated upon LPS treatment after 48 h and upon poly I:C treatment after 48 and 72 h. In addition, the result showed significant upregulations upon LPS and poly I:C treatment after 24 h. However, significant downregulation was also shown in the earlier phase after injection of poly I:C and L. garvieae in gills. Further, the binding affinity of recombinant LhGal B-like (rLhGal B-like) was evaluated using carbohydrate, pathogen-associated molecular patterns (PAMP) and bacterial binding assays. The rLhGal B-like could bind all the examined carbohydrates but had a higher affinity to α-lactose. PAMPs and bacterial binding experiments verified a wide range of PAMP molecules and bacterial strains that rLhGal B-like could bind to. Moreover, we examined the agglutination activity of rLhGal B-like, and the result showed that it could aggregate all the gram-positive and gram-negative bacteria. Taken together, our findings reveal the functional aspects of LhGal B-like as a PRR and the potential involvement of LhGal B-like in the innate immunity of redlip mullet.

Structural and functional analysis of a tandem repeat galacturonic acid-binding lectin from the sea hare Aplysia californica

A d-galacturonic acid-specific lectin, named AcL, was purified from the sea hare Aplysia californica by galactose-agarose affinity chromatography. AcL has a molecular mass of 27.5 kDa determined by MALDI-TOF mass spectrometry. This lectin shows a good affinity for d-galacturonic acid and a lower affinity for galactosides: raffinose, melibiose, α and β-lactose, and d-galactose. We determined the amino acid sequence of AcL by trypsin digestion and subsequent peptide analysis by mass spectrometry, resulting in a 238 amino acid protein with a theoretical molecular mass of 26.4 kDa. The difference between the theoretical and experimental values can be attributed to post-translational modifications. Thiol-disulfide quantification discerned five disulfide bonds and three free cysteines. The structure of Acl is mainly comprised of beta sheets, determined by circular dichroism, and predicted with AlphaFold. Theoretical models depict three nearly identical tandem domains consisting of two beta sheets each. From docking analysis, we identified AcL glycan-binding sites as multiple conserved motifs in each domain. Furthermore, phylogenetic analysis based on its structure and sequence showed that AcL and its closest homologues (GalULs) form a clear monophyletic group, distinct from other glycan-binding proteins with a jelly-roll fold: lectins of types F and H. GalULs possess four conserved sequence regions that distinguish them and are either ligand-binding motifs or stabilizing network hubs. We suggest that this new family should be referred to as GalUL or D-type, following the traditional naming of lectins; D standing for depilans, the epithet for the species (Aplysia depilans) from which a lectin of this family was first isolated and described.

Comparative study of structures and functional motifs in lectins from the commercially important photosynthetic microorganisms

Photosynthetic microorganisms, specifically cyanobacteria and microalgae, can synthesize a vast array of biologically active molecules, such as lectins, that have great potential for various biotechnological and biomedical applications. However, since the structures of these proteins are not well established, likely due to the presence of intrinsically disordered regions, our ability to better understand their functionality is hampered. We embarked on a study of the carbohydrate recognition domain (CRD), intrinsically disordered regions (IDRs), amino acidic composition, as well as and functional motifs in lectins from cyanobacteria of the genus Arthrospira and microalgae Chlorella and Dunaliella genus using a combination of bioinformatics techniques. This search revealed the presence of five distinctive CRD types differently distributed between the genera. Most CRDs displayed a group-specific distribution, except to C. sorokiniana possessing distinctive CRD probably due to its specific lifestyle. We also found that all CRDs contain short IDRs. Bacterial lectin of Arthrospira prokarionte showed lower intrinsic disorder and proline content when compared to the lectins from the eukaryotic microalgae (Chlorella and Dunaliella). Among the important functions predicted in all lectins were several specific motifs, which directly interacts with proteins involved in the cell-cycle control and which may be used for pharmaceutical purposes. Since the aforementioned properties of each type of lectin were investigated in silico, they need experimental confirmation. The results of our study provide an overview of the distribution of CRD, IDRs, and functional motifs within lectin from the commercially important microalgae.

In silico study reveals binding potential of rotenone at multiple sites of pulmonary surfactant proteins: A matter of concern

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Inhalation of rotenone exposes lung surfactant proteins (SP) to this pesticide.

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SP-A and SP-D provides protection from microbial infection.

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SP-B and SP-C maintain structure and respiratory function of lungs.

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Rotenone has potential to bind SPs at multiple sites.

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Such binding can subvert functions of SPs & may invite respiratory ailments.

Rotenone is a broad-spectrum pesticide employed in various agricultural practices all over the world. Human beings are exposed to this chemical through oral, nasal, and dermal routes. Inhalation of rotenone exposes bio-molecular components of lungs to this chemical. Biophysical activity of lungs is precisely regulated by pulmonary surfactant to facilitate gaseous exchange. Surfactant proteins (SPs) are the fundamental components of pulmonary surfactant. SPs like SP-A and SP-D have antimicrobial activities providing a crucial first line of defense against infections in lungs whereas SP-B and SP-C are mainly involved in respiratory cycle and reduction of surface tension at air–water interface. In this study, molecular docking analysis using AutoDock Vina has been conducted to investigate binding potential of rotenone with the four SPs. Results indicate that, rotenone can bind with carbohydrate recognition domain (CRD) of SP-A, N-, and C- terminal peptide of SP-B, SP-C, and CRD of SP-D at multiples sites via several interaction mediators such as H bonds, C–H bonds, alkyl bonds, pi-pi stacked, Van der Waals interaction, and other. Such interactions of rotenone with SPs can disrupt biophysical and anti-microbial functions of SPs in lungs that may invite respiratory ailments and pathogenic infections.

Antibacterial activity of four recombinant carbohydrate recognition domain proteins identified from the kuruma shrimp Marsupenaeus japonicus

The carbohydrate recognition domain (CRD) is the key component of C-type lectins (CTLs) with the capacity to recognize and eliminate invading pathogens. Herein, the recombinant proteins of four CRDs identified from the kuruma shrimp, Marsupenaeus japonicus, were produced and purified by an Escherichia coli expression system and affinity chromatography. Bacterial binding and antibacterial assays showed that the four CRDs displayed various bacterial binding and antibacterial activities against different bacteria. Among the four recombinant CRDs, His-CRD2-3 exhibited the broadest spectrum of bacterial binding and antibacterial activities against gram-negative bacteria (Vibrio parahaemolyticus, V. alginolyticus and V. harveyi) and gram-positive bacteria (Staphylococcus aureus and Micrococcus lysodeikticus). Moreover, the four recombinant CRDs showed different capacities to regulate the expression of several immune effector genes (MjCTL3, MjCTL4, MjCTL, Mjily and Mjsty), among which His-CRD2-3 displayed broader and stronger inductive effects on these immune effector genes. This study indicated that the four CRDs participated in immune defense by binding and killing bacteria and regulating the transcription of other immune effector genes. In addition, our results suggested that His-CRD2-3 might be a promising agent for the prevention and treatment of bacteriosis.

Production and Characterization of MIC1: A Lectin from Toxoplasma gondii

Some lectins of pathogens interact with host cells through the recognition of specific carbohydrates displayed on the mammals' cell surface. The microneme protein 1 (MIC1) from Toxoplasma gondii has a lectin domain that specifically binds sialic acid residues, often found in the terminal positions of N-glycans of mammalian cells. The necessary studies on the MIC1 biological roles have been limited initially by the laborious purification of the protein from T. gondii tachyzoites and the low yields verified. Then Escherichia coli has been transformed with a construct containing the MIC1 gene, and the obtained recombinant MIC1 (rMIC1) has been purified from the inclusion bodies. Herein, we detail the methodology of heterologous production and purification of rMIC1 and protocols to assay the rMIC1 lectin ability.

Structures of human galectin-10/monosaccharide complexes demonstrate potential of monosaccharides as effectors in forming Charcot-Leyden crystals

The galectins are a family of β-galactoside-specific animal lectins, and have attracted much attention as novel regulators of the immune system. Galectin-10 is well-expressed in eosinophils, and spontaneously forms Charcot-Leyden crystals (CLCs), during prolonged eosinophilic inflammatory reactions, which are frequently observed in eosinophilic diseases. Although biochemical and structural characterizations of galectin-10 have been done, its biological role and molecular mechanism are still unclear, and few X-ray structures of galectin-10 in complex with monosaccharides/oligosaccharides have been reported. Here, X-ray structures of galectin-10 in complexes with seven monosaccharides are presented with biochemical analyses to detect interactions of galectin-10 with monosaccharides/oligosaccharides. Galectin-10 forms a homo-dimer in the face-to-face orientation, and the monosaccharides bind to the carbohydrate recognition site composed of amino acid residues from two galectin-10 molecules of dimers, suggesting that galectin-10 dimer likely captures the monosaccharides in solution and in vivo. d-Glucose, d-allose, d-arabinose, and D-N-acetylgalactosamine bind to the interfaces between galectin-10 dimers in crystals, and they affect the stability of molecular packing in crystals, leading to easy-dissolving of CLCs, and/or inhibiting the formation of CLCs. These monosaccharides may serve as effectors of G10 to form CLCs in vivo.

MIC4 from Toxoplasma gondii: A Lectin Acting as a Toll-Like Receptor Agonist

Tachyzoites, which are infective forms of Toxoplasma gondii, use their actinomyosin system to move over surfaces and invade host cells. Central to this process is the regulated release of micronemes organelles contents. The microneme protein 4 (MIC4) has the property to recognize galactosides residues linked to glycoproteins on the host cell surface. This property allows that MIC4 binds to TLR2- and TLR4 N-linked glycans and promote the activation of cell innate immune cells and secretion of inflammatory cytokines, acting on resistance against the parasite. Obtention of MIC4 from T. gondii requires several purification steps, is time-consuming and provides low yield. Therefore, this section details the protocol for prokaryotic expression, production, and purification of recombinant MIC4 (rMIC4) and for experimental assays to confirm its biological activity.

Zebrafish intelectin 1 (zITLN1) plays a role in the innate immune response

Intelectin displays carbohydrate binding capacity and has been demonstrated to agglutinate bacteria, suggesting its role in innate immunity. It has also been linked to many pathogenic conditions in human. After reporting two amphioxus orthologs and the zebrafish intelectin 2 (zITLN2), here we cloned and characterized zebrafish intelectin 1 (zITLN1). Like zITLN2, zITLN1 also contains a conserved fibrinogen-related domain (FReD) and a unique intelectin domain (ITLN-D), expresses in all the tissues tested, with the highest level in intestine, and responds to bacterial challenge in acute phase. We also expressed zITLN1 in E. coli system, and purified recombinant zITLN1 could agglutinate both Gram-positive and Gram-negative bacteria in a calcium dependent manner. Its ability to agglutinate Gram-positive bacteria is stronger than that to Gram-negative bacteria whereas zITLN2 did not show such preference. This is probably due to the fact that recombinant zITLN1 could bind peptidoglycan (PGN) with a higher degree to lipopolysaccharide (LPS). Our results of zITLN1 provided new insight into the evolution and function of the intelectin family.

Characterisation and functional analysis of an L-type lectin from the swimming crab Portunus trituberculatus

L-type lectins are involved in glycoprotein secretion and are associated with immune responses. Herein, an L-type lectin was identified in swimming crab (Portunus trituberculatus). The 1347 bp PtLTL cDNA includes a 26 bp 5'-untranslated region (UTR), a 547 bp 3'-UTR with a poly(A) tail, and a 774 bp open reading frame encoding a 257 amino acid protein with a putative 21 residue signalling peptide. The protein includes an L-type lectin carbohydrate recognition domain containing four conserved cysteines. The 714 bp cDNA fragment encoding the mature peptide of PtLTL1 was recombined into pET-21a (+) with a C-terminally hexa-histidine tag fused in-frame and expressed in Escherichia coli Origami (DE3). Recombinant PtLTL1 caused agglutination of all three Gram-positive and Gram-negative bacterial strains tested. In addition, erythrocyte agglutination and LPS-binding activity were observed. PtLTL1 mRNA transcripts were most abundant in P. trituberculatus hepatopancreas and hemocytes, and expression was up-regulated in hemocytes challenged with Vibrio alginolyticus, suggesting PtLTL functions in the immune response against bacterial pathogens.

The N- and C-terminal carbohydrate recognition domains of Haemonchus contortus galectin bind to distinct receptors of goat PBMC and contribute differently to its immunomodulatory functions in host-parasite interactions

BACKGROUND

Hco-gal-m is a tandem-repeat galectin isolated from the adult worm of Haemonchus contortus. A growing body of studies have demonstrated that Hco-gal-m could exert its immunomodulatory effects on host peripheral blood mononuclear cells (PBMC) to facilitate the immune evasion. Our previous work revealed that C-terminal and N-terminal carbohydrate recognition domains (CRD) of Hco-gal-m had different sugar binding abilities. However, whether different domains of Hco-gal-m account differently for its multiple immunomodulatory functions in the host-parasite interaction remains to be elucidated.

RESULTS

We found that the N-terminal CRD of Hco-gal-m (MNh) and the C-terminal CRD (MCh) could bind to goat peripheral blood mononuclear cells by distinct receptors: transmembrane protein 63A (TMEM63A) was a binding receptor of MNh, while transmembrane protein 147 (TMEM147) was a binding receptor of MCh. In addition, MCh was much more potent than MNh in inhibiting cell proliferation and inducing apoptosis, while MNh was much more effective in inhibiting NO production. Moreover, MNh could suppress the transcription of interferon-γ (IFN-γ), but MCh not.

CONCLUSIONS

Our data suggested that these two CRDs of Hco-gal-m bind to distinct receptors and contributed differently to its ability to downregulate host immune response. These results will improve our understanding of galectins from parasitic nematodes contributing to the mechanism of parasitic immune evasion and continue to illustrate the diverse range of biological activities attributable to the galectin family.

X-ray structure of a protease-resistant mutant form of human galectin-9 having two carbohydrate recognition domains with a metal-binding site

Galectin-9 (G9) is a tandem-repeat type β-galactoside-specific animal lectin having N-terminal and C-terminal carbohydrate recognition domains (N-CRD and C-CRD, respectively) joined by a linker peptide that is involved in the immune system. G9 is divalent in glycan binding, and structural information about the spatial arrangement of the two CRDs is very important for elucidating its biological functions. As G9 is protease sensitive due to the long linker, the protease-resistant mutant form of G9 (G9Null) was developed by modification of the linker peptide, while retaining its biological functions. The X-ray structure of a mutant form of G9Null with the replacement of Arg221 by Ser (G9Null_R221S) having two CRDs was determined. The structure of G9Null_R221S was compact to associate the two CRDs in the back-to-back orientation with a large interface area, including hydrogen bonds and hydrophobic interactions. A metal ion was newly found in the galectin structure, possibly contributing to the stable structure of protein. The presented X-ray structure was thought to be one of the stable structures of G9, which likely occurs in solution. This was supported by structural comparisons with other tandem-repeated galectins and the analyses of protein thermostability by CD spectra measurements.

Bactericidal activity of fish galectin 4 derived membrane-binding peptide tagged with oligotryptophan

Galectins belong to the family of galactoside-binding proteins which act as pathogen recognition receptors by recognizing and binding to the carbohydrate present in the bacterial membranes. In this study, a Galectin-4 sequence was identified from the constructed cDNA library of Channa striatus and its structural features were reported. Gene expression analysis revealed that CsGal4 was highly expressed in liver and strongly induced by Epizootic Ulcerative Syndrome (EUS) causing pathogens such as Aphanomyces invadans, Aeromonas hydrophila and a viral analogue, poly I:C. To understand the antimicrobial role of putative dimerization site of CsGal4, the region was chemically synthesized and its bactericidal effect was determined. G4 peptide exhibited a weak bactericidal activity against Vibrio harveyi, an important aquaculture pathogen. We have also determined the bactericidal activity of the dimerization site by tagging pentamer oligotryptophan (W5) at the C-terminal of G4 peptide. Flow cytometry analysis revealed that G4W induced drastic reduction in cell counts than G4. Electron microscopic images showed membrane blebbings in V. harveyi which indicated the membrane disrupting activity of G4W. Interestingly, both the peptides did not exhibit any hemolytic activity and cytotoxicity towards peripheral blood cells of Channa striatus and the activity was specific only towards the bacterial membrane. Our results suggested that addition of W5 at the C-terminal of membrane-binding peptide remarkably improved its membrane disrupting activity.

Identification of C-type lectin-domain proteins (CTLDPs) in silkworm Bombyx mori

C-type lectins (CTLs) represent a large family of proteins that can bind carbohydrate moieties normally in a calcium-dependent manner. CTLs play important roles in mediating cell adhesion and the recognition of pathogens in the immune system. In the present study, we have identified 23 CTL genes in domestic silkworm Bombyx mori. CTL-domain proteins (CTLDPs) are classified into three groups based on the number of carbohydrate-recognition domains (CRDs) and the domain architectures. These include twelve CTL-S (Single-CRD), six immulectins (Dual-CRD) and five CTL-X (CRD with other domains). We studied their phylogenetic features, analyzed the conserved residues, predicted tertiary structures, and examined the tissue expression profile and immune inducibility. Through bioinformatics analysis, we have putatively identified ten secretory and two cytoplasmic CTL-S; four secretory and two cytoplasmic immulectins; one secretory, one cytoplasmic and three transmembrane forms of CTL-X. Most B. mori CTLDPs form monophyletic groups with orthologs from Lepidoptera, Diptera, Coleoptera and Hymenoptera species. Immulectins of B. mori and Manduca sexta evolved from common ancestor genes perhaps due to gene duplication events of CTL-S ancestor genes. Homology modeling revealed that the overall structures of B. mori CTL domains are analogous to those of humans with a variable loop region. We examined the expression profile of CTLDP genes in naïve and immune-stimulated tissues. The expression and induction of CTLDP genes were related to the tissues and microorganisms. Together, our gene identification, sequence comparison, phylogenetic analysis, homology modeling and expression analysis laid a good foundation for the further studies of B. mori CTLDPs and comparative genomics.

Molecular characterization of the lgals1 gene in large scale loach Paramisgurnus dabryanus

Galectins constitute a group of lectins with binding specificity for β-galactoside sugars. Galectin-1 is a prototype galectin and the multifunctionality of mammalian galectin-1s is well-known, but only a few of fish galectin-1s have been identified. In this study, we obtained the full-length cDNA and genomic sequence of the galectin-1 gene (designated as Pdlgals1) from large scale loach (Paramisgurnus dabryanus), performed phylogenetic analysis, and characterized the expression pattern and the transcriptional activity of its 5' flanking region. The Pdlgals1 gene contains 4 exons that encode a peptide of 132 amino acids with all the galectin signature motifs. Phylogenetic analysis and sequence alignment indicated that Pdlgals1 is a homologue of human LGALS1. RT-PCR and whole-mount in situ hybridization revealed that Pdlgals1 is mainly expressed in the skin, muscle, intestine and cavum oropharyngeum. Transcriptional activity assays demonstrated that the basal promoter of Pdlgals1 is located in a region from -500bp to its transcriptional start site. Potential binding sites for transcription factors including C/EBP, AP-1, GATA, Oct-1, δEF1, NF-κB, c-Myb, SP-1, AP-2, AML-1α, and AP-4 were identified in the basal promoter, suggesting that these factors are associated with the regulation of Pdlgals1. These results provided clues for further investigation of galectin-1 functions in loaches.

Recombinant expression, purification and preliminary biophysical and structural studies of C-terminal carbohydrate recognition domain from human galectin-4

Galectin-4 (Gal4), a tandem-repeat type galectin, is expressed in healthy epithelium of the gastrointestinal tract. Altered levels of Gal4 expression are associated with different types of cancer, suggesting its usage as a diagnostic marker as well as target for drug development. The functional data available for this class of proteins suggest that the wide spectrum of cellular activities reported for Gal4 relies on distinct glycan specificity and structural characteristics of its two carbohydrate recognition domains. In the present work, two independent constructs for recombinant expression of the C-terminal domain of human galectin-4 (hGal4-CRD2) were developed. His6-tagged and untagged recombinant proteins were overexpressed in Escherichia coli, and purified by affinity chromatography followed by gel filtration. Correct folding and activity of hGal4-CRD2 were assessed by circular dichroism and fluorescence spectroscopies, respectively. Diffraction quality crystals were obtained by vapor-diffusion sitting drop setup and the crystal structure of CRD2 was solved by molecular replacement techniques at 1.78 Å resolution. Our work describes the development of important experimental tools that will allow further studies in order to correlate structure and binding properties of hGal4-CRD2 and human galectin-4 functional activities.

NMR assignments of the C-terminal domain of human galectin-8

Galectins recognize β-galectosides to promote a variety of cellular functions. Despite their sequence variations, all galectins share the same carbohydrate recognition domains (CRD) and their modes of ligand recognition at a structural level are essentially identical. Human galectin 8 plays an important role in numerous cancer and immune responses. It consists of two CRDs that are connected via a flexible linker. The substrate affinities and specificities of the N- and C-terminal domains are quite different. In order to investigate the structural basis of their substrate specificities, we complete the NMR (1)H, (13)C, and (15)N chemical shift assignments of C-terminal domain of human galectin-8 (hG8C).

Snake venom galactoside-binding lectins: a structural and functional overview

Snake venom galactoside-binding lectins (SVgalLs) comprise a class of toxins capable of recognizing and interacting with terminal galactoside residues of glycans. In the past 35 years, since the first report on the purification of thrombolectin from Bothrops atrox snake venom, several SVgalLs from Viperidae and Elapidae snake families have been described, as has progressive improvement in the investigation of structural/functional aspects of these lectins. Moreover, the advances of techniques applied in protein-carbohydrate recognition have provided important approaches in order to screen for possible biological targets. The present review describes the efforts over the past 35 years to elucidate SVgalLs, highlighting their structure and carbohydrate recognition function involved in envenomation pathophysiology and potential biomedical applications.

Structural features, evolutionary relationships, and transcriptional regulation of C-type lectin-domain proteins in Manduca sexta

C-type lectins (CTLs) are a large family of Ca(2+)-dependent carbohydrate-binding proteins recognizing various glycoconjugates and functioning primarily in immunity and cell adhesion. We have identified 34 CTLDP (for CTL-domain protein) genes in the Manduca sexta genome, which encode proteins with one to three CTL domains. CTL-S1 through S9 (S for simple) have one or three CTL domains; immulectin-1 through 19 have two CTL domains; CTL-X1 through X6 (X for complex) have one or two CTL domains along with other structural modules. Nine simple CTLs and seventeen immulectins have a signal peptide and are likely extracellular. Five complex CTLs have both an N-terminal signal peptide and a C-terminal transmembrane region, indicating that they are membrane anchored. Immulectins exist broadly in Lepidoptera and lineage-specific gene duplications have generated three clusters of fourteen genes in the M. sexta genome, thirteen of which have similar expression patterns. In contrast to the family expansion, CTL-S1∼S6, S8, and X1∼X6 have 1:1 orthologs in at least four lepidopteran/dipteran/coleopteran species, suggestive of conserved functions in a wide range of holometabolous insects. Structural modeling suggests the key residues for Ca(2+)-dependent or independent binding of certain carbohydrates by CTL domains. Promoter analysis identified putative κB motifs in eighteen of the CTL genes, which did not have a strong correlation with immune inducibility in the mRNA or protein levels. Together, the gene identification, sequence comparisons, structure modeling, phylogenetic analysis, and expression profiling establish a solid foundation for future studies of M. sexta CTL-domain proteins.