Molecular characterization and biological effect of a C-type lectin receptor in Qihe crucian carp, Carassius auratus

C-type lectin receptors, as the important members of pattern-recognition receptors, play the crucial roles in the innate immune system, which discriminate self and non-self by recognizing and binding the carbohydrates on the surface of microorganism. In this study, we identified a C-type lectin receptor gene in Qihe crucian carp Carassius auratus (named as CaCLR). The full-length cDNA of CaCLR was composed of 1130 bp, with a 226 bp 5'-untranslated region (UTR), a 792 bp ORF encoding a 263aa protein, and a 112 bp 3'-UTR with a polyadenylation signal sequence AATAAA and a poly (A) tail. The predicted amino acid sequence of CaCLR is a single transmembrane receptor with a typical carbohydrate recognition domain (CRD) at its C-terminus. With regard to the mRNA transcript of CaCLR, it was ubiquitously detected in the tested tissues, among which it was the most abundant in head kidney. The temporal expressions of CaCLR were obviously up-regulated in liver, spleen, kidney, and head kidney after Aeromonas hydrophila and poly I: C challenge, respectively, and the patterns of expression changes were in a time-depended manner. The recombinant CaCLR (rCaCLR) purified from Escherichia coli BL21 (DE3), exhibited strong binding ability with lipopolysaccharide (LPS), peptidoglycan (PGN), β-Glucan, and Mannan, as well as five microorganisms including fungus (Saccharomyces cerevisiae), Gram-negative bacteria (A. hydrophila, E. coli and Vibrio anguillarum), and Gram-positive bacteria (Micrococcus lysodeikticus). In the presence of rCaCLR, the eliminating capacity against A. hydrophila could be enhanced in C. auratus. Taken together, CaCLR is involved in the antibacterial defense in C. auratus.

Potential Role of Platelet-Activating C-Type Lectin-Like Proteins in Viper Envenomation Induced Thrombotic Microangiopathy Symptom

Envenomation by viperid snakes may lead to severe bleeding, consumption coagulopathy, and thrombotic microangiopathy symptoms. The exact etiology or toxins responsible for thrombotic microangiopathy symptoms after snake envenomation remain obscure. Snake C-type lectin-like proteins (snaclecs) are one of the main non-enzymatic protein constituents in viper venoms, of which a majority are considered as modulators of thrombosis and hemostasis. In this study, we demonstrated that two snaclecs (mucetin and stejnulxin), isolated and identified from Protobothrops mucrosquamatus and Trimeresurus stejnegeri venoms, directly induced platelet degranulation and clot-retraction in vitro, and microvascular thrombosis has been confirmed in various organs in vivo. These snaclecs reduced cerebral blood flow and impaired motor balance and spatial memories in mice, which partially represent the thrombotic microangiopathy symptoms in some snakebite patients. The functional blocking of these snaclecs with antibodies alleviated the viper venom induced platelet activation and thrombotic microangiopathy-like symptoms. Understanding the pathophysiology of thrombotic microangiopathy associated with snake envenoming may lead to emerging therapeutic strategies.

Comprehensive Snake Venomics of the Okinawa Habu Pit Viper, Protobothrops flavoviridis, by Complementary Mass Spectrometry-Guided Approaches

The Asian world is home to a multitude of venomous and dangerous snakes, which are used to induce various medical effects in the preparation of traditional snake tinctures and alcoholics, like the Japanese snake wine, named Habushu. The aim of this work was to perform the first quantitative proteomic analysis of the Protobothrops flavoviridis pit viper venom. Accordingly, the venom was analyzed by complimentary bottom-up and top-down mass spectrometry techniques. The mass spectrometry-based snake venomics approach revealed that more than half of the venom is composed of different phospholipases A2 (PLA₂). The combination of this approach and an intact mass profiling led to the identification of the three main Habu PLA₂s. Furthermore, nearly one-third of the total venom consists of snake venom metalloproteinases and disintegrins, and several minor represented toxin families were detected: C-type lectin-like proteins (CTL), cysteine-rich secretory proteins (CRISP), snake venom serine proteases (svSP), l-amino acid oxidases (LAAO), phosphodiesterase (PDE) and 5'-nucleotidase. Finally, the venom of P. flavoviridis contains certain bradykinin-potentiating peptides and related peptides, like the svMP inhibitors, pEKW, pEQW, pEEW and pENW. In preliminary MTT cytotoxicity assays, the highest cancerous-cytotoxicity of crude venom was measured against human neuroblastoma SH-SY5Y cells and shows disintegrin-like effects in some fractions.

Identification and characterization of two novel C-type lectins from the larvae of housefly, Musca domestica L

Lectins and antimicrobial peptides (AMPs) are widely distributed in various insects and play crucial roles in primary host defense against pathogenic microorganisms. Two AMPs (cecropin and attacin) have been identified and characterized in the larvae of housefly. In this study, two novel C-type lectins (CTLs) were obtained from Musca domestica, while their agglutinating and antiviral properties were evaluated. Real-time PCR analysis showed that the mRNA levels of four immune genes (MdCTL1, MdCTL2, Cecropin, and Attacin) from M. domestica were significantly upregulated after injection with killed Gram-negative Escherichia coli. Moreover, purified MdCTL1-2 proteins can agglutinate E. coli and Staphylococcus aureus in the presence of calcium ions, suggesting their immune function is Ca²⁺ dependent. Sequence analysis indicated that typical WND and QPD motifs were found in the Ca²⁺ -binding site 2 of carbohydrate recognition domain from MdCTL1-2, which was consistent with their agglutinating activities. Subsequently, antiviral experiments indicated that MdCTL1-2 proteins could significantly reduce the infection rate of Spodoptera frugiperda 9 cells by the baculovirus Autographa californica multicapsid nucleopolyhedrovirus, indicating they might play important roles in insect innate immunity against microbial pathogens. In addition, MdCTL1-2 proteins could effectively inhibit the replication of influenza H₁ N₁ virus, which was similar to the effect of ribavirin. These results suggested that two novel CTLs could be considered a promising drug candidate for the treatment of influenza. Moreover, it is believed that the discovery of the CTLs with antiviral effects in M. domestica will improve our understanding of the molecular mechanism of insect immune response against viruses.

Stejnulxin, a novel snake C-type lectin-like protein from Trimeresurus stejnegeri venom is a potent platelet agonist acting specifically via GPVI

Stejnulxin, a novel snake C-type lectin-like protein with potent platelet activating activity, was purified and characterized from Trimeresurus stejnegeri venom. Under non-reducing conditions, it migrated on a SDS-polyacrylamide gel with an apparent molecular mass of 120 kDa. On reduction, it separated into three polypeptide subunits with apparent molecular masses of 16 kDa (α), 20 kDa (β1) and 22 kDa (β2), respectively. The complete amino acid sequences of its subunits were deduced from cloned cDNAs. The N-terminal sequencing and cDNA cloning indicated that β1 and β2 subunits of stejnulxin have identical amino acid sequences and each contains two N-glycosylation sites. Accordingly, the molecular mass difference between β1 and β2 is caused by glycosylation heterogenity. The subunit amino acid sequences of stejnulxin are similar to those of convulxin, with sequence identities of 52.6% and 66.4% for the α and β, respectively. Stejnulxin induced human platelet aggregation in a dose-dependent manner. Antibodies against αIIbβ3 inhibited the aggregation response to stejnulxin, indicating that activation of αIIbβ3 and binding of fibrinogen are involved in stejnulxin-induced platelet aggregation. Antibodies against GPIbα or α2β1 as well as echicetin or rhodocetin had no significant effect on stejnulxin-induced platelet aggregation. However, platelet activation induced by stejnulxin was blocked by anti-GPVI antibodies. In addition, stejnulxin induced a tyrosine phosphorylation profile in platelets that resembled that produced by convulxin. Biotinylated stejnulxin bound specifically to platelet membrane GPVI.

Identification and preliminary characterization of a putative C-type lectin receptor-like protein in the T. cruzi tomato lectin endocytic-enriched proteome

Trypanosoma cruzi, the etiological agent of the Chagas' disease in Latin America undergoes a complex life cycle involving two hosts, a mammalian host and a reduviid insect vector (triatomine). In the insect midgut the parasite multiplies as epimastigote forms, which rely on endocytosis for their energy requirement. We recently showed that posttranslational modification of endocytic N-glycoproteins by tomato lectin (TL) binding-N-glycans is crucial for receptor-mediated endocytosis (RME) in epimastigote forms. In an attempt to characterize the endocytic proteome we used a TL affinity chromatography, which significantly enriched glycoproteins of the trypanosomal endocytic pathway. In addition to various lysosomal hydrolases, we found an endosomal C-type lectin-like protein, which displays some structural and topological characteristics of the mammalian lectin receptor superfamily. This lectin encoding a large transmembrane protein of around 375kDa contained three putative extracellular N-terminal C-type lectin domains (CTLD) and located inside the flagellar pocket (FP)/cytostome and endosomal compartments of the insect stage of the parasite and on the surface of the plasma membrane of intracellular amastigote parasites. Noteworthy, this endogenous lectin displayed similar sugar-binding specificity to that of TL and therefore could be important in either the N-glycan mediated endocytosis or parasite adhesion to host cells. We postulated that during the evolution of trypanosomatids, genes encoding lectin harboring 3 CTDLs represent an old acquisition present in free-living, monoxenic and heteroxenic trypanosomatids, which would have been secondarily lost in extracellular parasites from the T. brucei clade.

Molecular cloning and analysis of a C-type lectin from silkworm Bombyx mori

C-type lectins (CTLs) play a variety of roles in plants and animals. They are involved in animal development, pathogen recognition, and the activation of immune responses. CTLs carry one or more non-catalytic carbohydrate-recognition domains (CRDs) to bind specific carbohydrates reversibly. Here, we report the molecular cloning and functional analysis of a single-CRD CTL, named C-type lectin-S2 (BmCTL-S2) from the domesticated silkmoth Bombyx mori (Lepidoptera: Bombycidae). The ORF of CTL-S2 is 666 bp, which encodes a putative protein of 221 amino acids. BmCTL-S2 is expressed in a variety of immune-related tissues, including hemocytes and fat body among others. BmCTL-S2 mRNA level in the midgut and the fat body was significantly increased by bacterial challenges. The recombinant protein (rBmCTL-S2) bound different bacterial cell wall components and bacterial cells. rBmCTL-S2 also inhibited the growth of Bacillus subtilis and Staphylococcus aureus. Taken together, we infer that BmCTL-S2 is a pattern-recognition receptor with antibacterial activities.

Mass spectrometry guided venom profiling and bioactivity screening of the Anatolian Meadow Viper, Vipera anatolica

This contribution reports on the first characterization of the venom proteome and the bioactivity screening of Vipera anatolica, the Anatolian Meadow Viper. The crude venom as well as an isolated dimeric disintegrin showed remarkable cytotoxic activity against glioblastoma cells. Due to the rare occurrence and the small size of this species only little amount of venom was available, which was profiled by means of a combination of bottom-up and top-down mass spectrometry. From this analysis we identified snake venom metalloproteases, cysteine-rich secretory protein isoforms, a metalloprotease inhibitor, several type A2 phospholipases, disintegrins, a snake venom serine protease, a C-type lectin and a Kunitz-type protease inhibitor. Furthermore, we detected several isoforms of above mentioned proteins as well as previously unknown proteins, indicating an extensive complexity of the venom which would have remained undetected with conventional venomic approaches.

A new C-type lectin (RVsnaclec) purified from venom of Daboia russelii russelii shows anticoagulant activity via inhibition of FXa and concentration-dependent differential response to platelets in a Ca²⁺-independent manner

This is the first report on the characterization of a snaclec (RVsnaclec) purified from Daboia russelii russelii venom. The RVsnaclec is a heterodimer of two subunits, α (15.1 kDa) and β (9 kDa). These subunits are covalently linked to form multimeric (αβ)₂ and (αβ)₄ structures. Peptide mass fingerprinting analysis of RVsnaclec via LC-MS/MS demonstrated its similarity to snaclecs purified from other viperid snake venoms. Two tryptic peptide sequences of RVsnaclec revealed the putative conserved domains of C-type lectin (CTL). RVsnaclec dose-dependently increased the Ca-clotting time and prothrombin time of platelet-poor plasma (PPP); however, it did not affect the partial thromboplastin time (APTT) or thrombin time of PPP. The in vitro and in vivo anticoagulant activity of RVsnaclec is correlated to its binding and subsequent uncompetitive inhibition of FXa (Ki = 0.52 μmole) in a Ca(2+)-independent manner; however, supplementation with 0.25 mM Ca(2+) enhanced the Xa binding potency of RVsnaclec. Monovalent or polyvalent antivenom failed to neutralize its anticoagulant potency, and RVsnaclec did not inhibit trypsin, chymotrypsin, thrombin or plasmin. RVsnaclec was devoid of hemolytic activity or cytotoxicity against several human cancer cell lines, demonstrated concentration-dependent aggregation and deaggregation of human platelets, and inhibited the ADP-induced aggregation of platelet. RVsnaclec (5.0 mg/kg body weight) was non-lethal to mice and showed no adverse pharmacological effects, suggesting that it has potential as a lead compound for future therapeutic applications in cardiovascular disorders.

Molecular cloning and expression analysis of mannose receptor C type 1 in grass carp (Ctenopharyngodon idella)

Mannose receptor C type 1 (MRC1) is a pattern-recognition receptor (PRR) which plays a significant role in immune responses. Much work on MRC1 has been done in mammals and birds while little in fish. In this study, we cloned and characterized MRC1 in grass carp (gcMR). The full-length gcMR contained 5291bp encoding a putative protein of 1432 amino acids. The predicted amino acid sequences showed that gcMR contained a signal peptide, a cysteine-rich (CR) domain, a fibronectin type II (FN II) domain, eight C-type lectin-like domains (CTLDs), a transmembrane domain and a short cytoplasmic domain. gcMR were constitutively expressed in different organs with the higher expression in spleen and head kidney. During embryonic development, gcMR transcript levels were highest at cleavage stage. The up-regulation expression of gcMR, IL-1β and TNF-α in liver, spleen, head kidney and intestine after Aeromonas hydrophila infection indicating it involved in innate immune regulation during bacterial infections.

Tat peptide-mediated soluble expression of the membrane protein LSECtin-CRD in Escherichia coli

The human liver and lymph node sinusoidal endothelial cell C-type lectin (hLSECtin), a type II integral membrane protein, containing a Ca²⁺-dependent carbohydrate recognition domain (CRD), has a well-established biological activity, yet its three-dimensional structure is unknown due to low expression yields and aggregation into inclusion bodies. Previous study has demonstrated that the HIV-1 virus-encoded Tat peptide (‘YGRKKRRQRRR’) can increase the yields and the solubility of heterologous proteins. However, whether the Tat peptide could promote the high-yield and soluble expression of membrane proteins in Escherichia coli is not known. Therefore, the prokaryotic expression vector pET28b-Tat-hLSECtin-CRD (using pET28b and pET28b-hLSECtin-CRD as controls) was constructed, and transformed into E. coli BL21 (DE3) cells and induced with isopropyl-β-d-thiogalactoside (IPTG) followed with identifying by SDS-PAGE and Western blot. Subsequently, the bacterial subcellular structure, in which overexpressed the heterologous proteins Tat-hLSECtin-CRD and Tat-free hLSECtin-CRD, was analyzed by transmission electron microscope (TEM) respectively, and the mannose-binding activity of Tat-hLSECtin-CRD was also determined. Expectedly, the solubility of Tat-LSECtin-CRD significantly increased compared to Tat-free LSECtin-CRD (**p < 0.01) with prolonged time, and the Tat-LSECtin-CRD had a significant mannose-binding activity. The subcellular structure analysis indicated that the bacterial cells overexpressed Tat-hLSECtin-CRD exhibited denser region compared with controls, while dot denser region aggregated in the two ends of bacterial cells overexpressed Tat-free hLSECtin-CRD. This study provided a novel method for improving the soluble expression of membrane proteins in prokaryotic systems by fusion with the Tat peptide, which may be potentially expanded to the expression of other membrane proteins.

A novel lectin domain-containing protein (LvCTLD) associated with response of the whiteleg shrimp Penaeus (Litopenaeus) vannamei to yellow head virus (YHV)

When using mRNA from gills of normal whiteleg shrimp Penaeus (Litopenaeus) vannamei as the tester and mRNA from yellow head virus (YHV)-infected shrimp as the driver, subtractive suppression hybridization (SSH) revealed that a novel EST clone of 198 bp with a putative C-type lectin-like domain (CTLD) was downregulated in YHV-infected shrimp. The clone nucleotide sequence had 99% identity with one contig MGID1052359 (1,380 bp) reported in an EST database of P. vannamei, and the presence of this target in normal shrimp was confirmed by RT-PCR using primers designed from the MGID1052359 sequence. Analysis of the primary structure of the deduced amino acid (a.a.) sequence of the contig revealed a short portion (40 a.a. residues) at its N-terminus with high similarity to a low density lipoprotein receptor (LDLR) class A domain and another 152 a.a. residues at its C-terminus with high similarity to a C-type lectin domain. Thus, the clone was named LvCTLD and three recombinant proteins (LvCTLD, the LDLR domain and the CTLD domain) were synthesized in a bacterial system based on its sequence. An in vitro encapsulation assay revealed that Sepharose 4B beads coated with rLvCTLD were encapsulated by shrimp hemocytes and that melanization followed by 24 h post-encapsulation. The encapsulation activity of rLvCTLD was inhibited by 100 mM galactose, but not mannose or EDTA. In vivo injection of rLvCTLD or rLvCTLD plus YHV resulted in a significant elevation of PO activity in the hemolymph of the challenged shrimp when compared to shrimp injected with buffer, suggesting that rLvCTLD could activate the proPO system. An ELISA test revealed that rLvCTLD could bind to YHV particles in the presence of shrimp hemolymph. Phylogenetic analysis suggested that the LvCTLD sequence was more closely related to an antiviral gene found in Penaeus monodon (PmAV) than to other reported shrimp lectins. Taken together, we conclude that a novel shrimp LvCTLD is a host recognition molecule involved in the shrimp defense mechanism against YHV via recruitment of hemocytes, probably at the site of viral infection, and via activation of the proPO system.

C-type lectin from red swamp crayfish Procambarus clarkii participates in cellular immune response

Lectins are potential immune recognition proteins. In this study, a novel C-type lectin (Pc-Lec1) is reported in freshwater crayfish Procambarus clarkii. Pc-Lec1 encodes a protein of 163 amino acids with a putative signal peptide and a single carbohydrate recognition domain. It was constitutively expressed in various tissues of a normal crayfish, especially in the hepatopancreas and gills. Expressions of Pc-Lec1 were up-regulated in the hepatopancreas and gills of crayfish challenged with Vibrio anguillarum, Staphylococcus aureus, or the white spot syndrome virus. Recombinant mature Pc-Lec1 bound bacteria and polysaccharides (peptidoglycan, lipoteichoic acid, and lipopolysaccharide) but did not agglutinate bacteria. Pc-Lec1 enhanced hemocyte encapsulation of the sepharose beads in vitro, and the blocking of beads by a polyclonal antibody inhibited encapsulation. Pc-Lec1 promoted clearance of V. anguillarum in vivo. These results suggest that Pc-Lec1 is a pattern recognition receptor and participates in cellular immune response. Pc-Lec1 performs its function as an opsonin by enhancing the encapsulation or clearance of pathogenic bacteria.

[Identification of the novel platelet activation receptor CLEC-2 and Its pathological and physiological roles]

We have identified a novel class of platelet activation receptor, CLEC-2, as a receptor for rhodocytin, a platelet-activating snake venom. CLEC-2 activation leads to tyrosine phosphorylation of the YITL motif in its cytoplasmic tail, the binding of Syk, initiation of downstream tyrosine phosphorylation events, and activation of phodpholipas Cgamma2, which result in platelet aggregation. We also identified podoplanin as an internal ligand for CLEC-2. Podoplanin is expressed on the surface of tumor cells and facilitates tumor metastasis by inducing platelet aggregation. We showed that an antibody that blocked the binding between CLEC-2 and podoplanin inhibited tumor metastasis using an experimental lung metastasis model in mice. Podoplanin is also expressed in lymphatic endothelial cells, but the physiological role of the interaction between CLEC-2 and podoplanin in lymphatic endothelial cells has not been elucidated. We generated CLEC-2-deficient mice, and found that these mice die in the embryonic/neonatal stages, associated with disorganized and blood-filled lymphatic vessels and severe edema. Moreover, through the transplantation of fetal liver cells from CLEC-2 +/+ or CLEC-2-/- embryos, we were able to demonstrate that CLEC-2 is involved in thrombus stabilization in vitro and in vivo, possibly through homophilic interactions without any apparent increase in the bleeding tendency. These findings revealed that CLEC-2 plays a crucial role in not only tumor metastasis, but also in lymphangiogenesis and thrombus stabilization. We propose that CLEC-2 could be an ideal novel target protein for an anti-platelet drug, which inhibits pathological thrombus formation but not physiological hemostasis, as well as a novel target protein for an anti-metastatic drug.

Structure of natural killer cell receptor KLRG1 bound to E-cadherin reveals basis for MHC-independent missing self recognition

The cytolytic activity of natural killer (NK) cells is regulated by inhibitory receptors that detect the absence of self molecules on target cells. Structural studies of missing self recognition have focused on NK receptors that bind MHC. However, NK cells also possess inhibitory receptors specific for non-MHC ligands, notably cadherins, which are downregulated in metastatic tumors. We determined the structure of killer cell lectin-like receptor G1 (KLRG1) in complex with E-cadherin. KLRG1 mediates missing self recognition by binding to a highly conserved site on classical cadherins, enabling it to monitor expression of several cadherins (E-, N-, and R-) on target cells. This site overlaps the site responsible for cell-cell adhesion but is distinct from the integrin alpha(E)beta(7) binding site. We propose that E-cadherin may coengage KLRG1 and alpha(E)beta(7) and that KLRG1 overcomes its exceptionally weak affinity for cadherins through multipoint attachment to target cells, resulting in inhibitory signaling.

Production and characterization of the recombinant Islet Neogenesis Associated Protein (rINGAP)

Islet Neogenesis Associated Protein (INGAP) is implicated in pancreatic islet neogenesis. INGAP peptide, a pentadecapeptide comprising amino acids 104-118, reverses diabetes in rodents and improves glucose homeostasis in patients with diabetes. The mechanism of INGAP action is unknown, but such studies would benefit from the availability of the full-length recombinant protein (rINGAP). Here we report the production of rINGAP from 293-SF cells following lentiviral transduction, and its characterization by MALDI-TOF and Q-TOF Mass Spectrometry, and HPLC. Importantly, we show that rINGAP exhibits 100x the bioactivity of INGAP peptide on a molar basis in an in vitro assay of human islet regeneration.

The highly specific platelet glycoprotein (GP) VI agonist trowaglerix impaired collagen-induced platelet aggregation ex vivo through matrix metalloproteinase-dependent GPVI shedding

BACKGROUND

C-type lectin proteins (CLPs) have diverse targets including platelet GPIb, GPVI and integrin alpha(2)beta(1), and affect platelet function in a various way. In this study, we characterized a huge, heterodimeric venom protein, trowaglerix, which belongs to the CLP family.

METHODS

We purified a potent platelet-aggregation inducer, trowaglerix, from the crude venom of Tropidolaemus wagleri. Biotinylated trowaglerix was used for binding assays, and immunoblotting was used to investigate the signal transduction involved.

RESULTS

Two distinct subunits of trowaglerix with similar masses of around 16 kDa were eluted by high-performance liquid chromatography after reduction and alkylation. Trowaglerix induced platelet aggregation of washed human platelets and platelet-rich plasma (PRP) in a concentration-dependent manner. Biotinylated trowaglerix specifically bound to platelet membrane GPVI, but not to GPIb or alpha(2) integrin. Treatment with trowaglerix induced GPVI loss in human platelets in vitro and impaired the platelet aggregation of mouse PRP ex vivo in response to collagen but not in response to adenosine diphosphate (ADP). However, GM6001, a matrix metalloproteinase (MMP) inhibitor, inhibited trowaglerix-induced GPVI cleavage and restored the platelet responsiveness of PRP to collagen.

CONCLUSIONS

Trowaglerix activates platelets through specific binding to GPVI, leading to kinases-dependent exposure of functional alpha(IIb)beta(3) and platelet aggregation, and also induces MMP-dependent GPVI shedding from platelets.

Overproduction, purification and preliminary crystallographic analysis of the carbohydrate-recognition domain of human langerin

Langerin, a lectin that is specific to Langerhans cells, interacts with glycoconjugates through its carbohydrate-recognition domain (CRD). This carbohydrate binding occurs by an avidity-based mechanism that is enabled by the neck domain responsible for trimerization. Langerin binds HIV through its CRD and thus plays a protective role against its propagation by the internalization of virions in Birbeck granules. Here, the overproduction, purification and crystallization of the langerin CRD is reported. Crystals obtained by the hanging-drop vapour-diffusion method allowed the collection of a complete data set to 1.5 A resolution and belonged to the tetragonal space group P4(2), with unit-cell parameters a = b = 79.55, c = 90.14 A.

A hepatopancreas-specific C-type lectin from the Chinese shrimp Fenneropenaeus chinensis exhibits antimicrobial activity

Lectins play important roles in animal innate immune responses by serving as pattern recognition receptors, opsonins, or effector molecules. Here, we report a novel hepatopancreas-specific C-type lectin, designated Fc-hsL, from the hepatopancreas of the Chinese shrimp, Fenneropenaeus chinensis. The cDNA of Fc-hsL is 571 bp long with a 480 bp open reading frame that encodes a 159-residue protein. Fc-hsL contains a signal peptide and a single C-type lectin-like domain (CTLD) or carbohydrate recognition domain (CRD). It has an EPN(Glu-Pro-Asn) motif with a predicted ligand-binding site specific for mannose. Fc-hsL was constitutively expressed in the hepatopancreas of normal shrimp, and its expression was up-regulated following challenge of shrimp with bacteria or virus. Fc-hsL was not detected in other tissues but was induced in the stomach of immune-challenged shrimp. Fc-hsL protein was detected in both hemolymph and the hepatopancreas of bacteria- and virus-challenged shrimp. Recombinant mature Fc-hsL has no hemagglutinating activity, but calcium-dependent agglutinating activity against some Gram-positive and Gram-negative bacteria was detected. The rFc-hsL also has binding activity to some Gram-positive and Gram-negative bacteria and high antimicrobial activity against some bacteria and fungi. These in vitro functions of recombinant Fc-hsL were calcium-independent. Fc-hsL may act as a pattern recognition receptor in antibacterial defense and as an effector in innate immunity of Chinese shrimp.

In vivo targeting of DC-SIGN-positive antigen-presenting cells in a nonhuman primate model

In vivo targeting of antigen-presenting cells (APCs) with antigens coupled to antibodies directed against APC-specific endocytic receptors is a simple and a promising approach to induce or modulate immune responses against those antigens. In a recent in vitro study, we have shown that targeting of APCs with an antigen coupled to an antibody directed against the endocytic receptor DC-SIGN effectively induces a specific immune response against that antigen. The aim of the present study was to determine the ability of the murine antihuman DC-SIGN antibody AZN-D1 to target APCs in a cynomolgus macaque model after its administration in vivo. Immunohistochemical analysis demonstrated that macaques injected intravenously with AZN-D1 have AZN-D1-targeted APCs in all lymph nodes (LNs) tested and in the liver. DC-SIGN-positive cells were mainly located in the medullary sinuses of the LNs and in the hepatic sinusoids in the liver. No unlabeled DC-SIGN molecules were found in the LN of AZN-D1-injected macaques. Morphologic criteria and staining of sequential LN sections with a panel of antibodies indicated that the DC-SIGN-targeted cells belong to the myeloid lineage of APCs. In conclusion, this is the first study that shows specific targeting of APCs in vivo by using antibodies directed against DC-SIGN.

Comparative studies of the anti-leishmanial activity of three Crotalus durissus ssp. venoms

In this study, we compared the anti-leishmanial activity of three crotalic venoms (Crotalus durissus terrificus-Cdt, Crotalus durissus cascavella-Cdca, and Crotalus durissus collilineatus-Cdcol). Different concentrations of each venom incubated with Leishmania (Leishmania) amazonensis promastigotes were used. Cdt venom exhibited a higher anti-leishmanial activity (Inhibitory concentration-IC50-value of 4.70+/-1.72 microg/ml) in comparison with that of Cdca venom (IC50 value of 9.41+/-1.21 microg/ml), while Cdcol venom increased parasite numbers in 50% at a concentration of 44.30+/-2.18 microg/ml. In addition, this venom showed a low anti-leishmanial activity in higher concentrations (IC50 value of 281.00+/-9.50 microg/ml). The main fractions of Cdca venom were isolated and assayed under similar conditions used for assessing crude venom. The most active fractions were gyroxin and crotamine that had IC50 values of 3.80+/-0.52 microg/ml and 19.95+/-4.21 microg/ml, respectively. Convulxin also inhibited parasite growth rate, although this effect was not dose-dependent. Crotoxin was the least effective fraction with an IC50 value of 99.80+/-2.21 microg/ml. None of the protein fractions presented cytotoxic effects against J774 cells in culture. In vivo assays using BALB/c mice revealed that crotoxin and crotamine were the main toxic fractions. In conclusion, C. durissus cascavella venom has three main fractions with anti-leishmanial activity. These results open new possibilities to find proteins that might be used as possible agents against cutaneous leishmaniasis.

Expression and localization of CHODLDeltaE/CHODLfDeltaE, the soluble isoform of chondrolectin

The C-type lectin family is a group of animal proteins which can be distinguished from other lectins by the presence of a Ca2+-dependent carbohydrate recognition domain (CRD) in their protein sequence. They are classified into 17 groups according to their domain architecture and have a wide variety of functions. The human chondrolectin gene encodes transmembrane (CHODL, CHODLf) and soluble proteins (CHODLDeltaE, CHODLfDeltaE) belonging to the family of C-type lectins because of the presence of one CRD domain in their N-terminal region. The CHODL splice variants (CHODLf, CHODLDeltaE and CHODLfDeltaE) are differentially expressed in T lymphocytes. The transmembrane-containing isoform CHODLf is localized in the ER-Golgi apparatus. CHODLDeltaE and CHODLfDeltaE are devoid of the transmembrane domain and terminate in QDEL, an ER retention signal. In this paper we have investigated the expression of the CHODLDeltaE/CHODLfDeltaE protein. This variant localizes in the late endoplasmic reticulum. We detected the protein in spleen and tonsils in a small population of lymphocytes. Moreover, the isoform seems to be differentially expressed in thymocytes and lymphocytes suggesting an important biological function during T cell development.

Isolation, Cloning, and Characterization of a Novel Phosphomannan-binding Lectin from Porcine Serum

Mannan-binding protein (MBP) is a C-type serum lectin that is an important constituent of the innate immune defense because it activates the complement system via the lectin pathway. While the pig has been proposed to be an attractive source of xenotransplantable tissues and organs, little is known about porcine MBP. In our previous studies, phosphomannan, but not mannan, was found to be an effective inhibitor of the C1q-independent bactericidal activity of newborn piglet serum against some rough strains of Gram-negative bacteria. In contrast, the inhibitory activities of phosphomannan and mannan were very similar in the case of MBP-dependent bactericidal activity against rough strains of Escherichia coli K-12 and S-16. Based on these findings, we inferred that an MBP-like lectin with slightly or completely different carbohydrate binding specificity might exist in newborn piglet serum and be responsible for the C1q-independent bactericidal activity. Herein we report that a novel phosphomannan-binding lectin (PMBL) of 33 kDa under reducing conditions was isolated from both newborn and adult porcine serum and characterized. Porcine PMBL functionally activated the complement system via the lectin pathway triggered by binding with both phosphomannan (P-mannan) and mannan, which, unlike MBP, was effectively inhibited by mannose 6-phosphate- or galatose-containing oligosaccharides. Our observations suggest that porcine PMBL plays a critical role in the innate immune defense from the newborn stage to adult-hood, and the establishment of a newborn piglet experimental model for the innate immune system studies is a valuable step toward elucidation of the physiological function and molecular mechanism of lectin pathway.

Amino acid sequence and characterization of C-type lectin purified from the snake venom of Crotalus ruber

Galactoside-binding lectin was purified from the snake venom of Crotalus ruber by affinity chromatography on a lactose-agarose column, and the complete amino acid sequence was determined. The C. ruber venom lectin (CRL) showed a single band of 28 kDa by SDS-polyacrylamide electrophoresis under non-reducing conditions, but it showed a single band of 15 kDa under reducing conditions, indicating that CRL is a disulfide-linked homodimer of 15 kDa subunit. CRL specifically recognized beta-galactosides such as thiodigalactoside followed by N-acetylgalactosamine when examined with their inhibitory effects on CRL-induced hemagglutination. A CRL subunit was composed of 135 residues containing nine Cys residues and showed a high similarity to other C-type galactoside-binding lectins from snake venoms. C. atrox lectin (CAL) showed almost the same sequence except for eight amino acid residues. Neither CRL nor CAL induced platelet aggregation by itself or inhibited platelet aggregation mediated by von Willebrand factor or fibrinogen with agonists. CRL showed a similar oligomeric form and the sugar specificity as CAL, but it showed different divalent cation sensitivity such as Mn(2+) and Ni(2+). Homology modeling suggested that the amino acid substitution found in CRL does not affect sugar recognition of the lectin but might alter the conformation and influence the sugar binding pocket induced by the metal-ion binding.

Pancreatitis-associated protein: From a lectin to an anti-inflammatory cytokine

Pancreatitis-associated protein (PAP) was discovered in the pancreatic juice of rats with acute pancreatitis. PAP is a 16 kDa secretory protein structurally related to the C-type lectins although classical lectin-related function has not been reported yet. Then, it was demonstrated that PAP expression may be activated in some tissues in a constitutive or injury- and inflammation-induced manner. More recently, it has been found that PAP acts as an anti-inflammatory factor in vitro and in vivo. PAP expression can be induced by several pro- and anti-inflammatory cytokines and by itself through a JAK/STAT3-dependent pathway. PAP is able to activate the expression of the anti-inflammatory factor SOCS3 through the JAK/STAT3-dependent pathway. The JAK/STAT3/SOCS3 pathway seems to be a common point between PAP and several cytokines. Therefore, it is reasonable to propose that PAP is a new anti-inflammatory cytokine.

Lebectin, aMacrovipera lebetina venom-derived C-type lectin, inhibits angiogenesis both in vitro and in vivo

Integrins play an essential role in endothelial cell motility processes during angiogenesis and thus present interesting targets for the development of new anti-angiogenic agents. Snake venoms naturally contain a variety of proteins that can affect integrin-ligand interactions. Recently, the C-type lectin proteins (CLPs) have been characterized as efficient modulators of integrin functions. In this study, we investigated the anti-angiogenic activity of lebectin, a newly discovered CLP from Macrovipera lebetina venom. Human brain microvascular endothelial cells (HBMEC), used as an in vitro model, express alphavbeta3, alphavbeta5, and alpha5beta1 integrins, as well as the alpha2, alpha3, alpha6, and beta4 subunits. Our data show that lebectin acts as a very potent inhibitor (IC(50) approximately 0.5 nM) of HBMEC adhesion and migration on fibronectin by blocking the adhesive functions of both the alpha5beta1 and alphaV integrins. In addition, lebectin strongly inhibits both HBMEC in vitro tubulogenesis on Matrigel trade mark (IC(50) = 0.4 nM) and proliferation. Finally, using both a chicken CAM assay and a Matrigel trade mark Plug assay in nude mice, our results show that lebectin displays potent anti-angiogenic activity in vivo. Lebectin thus represents a new C-type lectin with anti-angiogenic properties with great potential for the treatment of angiogenesis-related diseases.

A system for concomitant overexpression of four periplasmic folding catalysts to improve secretory protein production in Escherichia coli

Although Escherichia coli is in wide use for preparative protein expression, problems with the folding of the recombinant gene product and protein aggregation are frequently encountered. Apart from cytoplasmic expression, this is also true for secretion into the bacterial periplasm, the method of choice for the production of proteins that carry structural disulfide bonds. Here we report the construction of the helper plasmid pTUM4, which effects overexpression of four established periplasmic chaperones and folding catalysts: the thiol-disulfide oxidoreductases DsbA and DsbC that catalyze the formation and isomerization of disulfide bridges and the peptidyl-prolyl cis/trans-isomerases with chaperone activity, FkpA and SurA. pTUM4 carries a p15a origin of replication and a chloramphenicol resistance gene and, thus, it is compatible with many conventional expression vectors that use the ColEI origin and an ampicillin resistance. Its positive effects on the yield of soluble recombinant protein and the homogeneity of disulfide pattern are illustrated here using the human plasma retinol-binding protein as well as the extracellular carbohydrate recognition domain of the dendritic cell membrane receptor DC-SIGN. Hence, pTUM4 represents a novel helper vector which complements existing cytosolic chaperone coexpression plasmids and should be useful for the functional secretion of various recombinant proteins with hampered folding efficiency.

Purification and biological effects of C-type lectin isolated from Bothrops insularis venom

Bothrops insularis is a snake from Queimada Grande Island, which is an island located about 20 miles away from the southeastern coast of Brazil. Compared to other Brazilian species of Bothrops, the toxinology of B. insularis is still poorly understood. Its C-type lectin is involved in several biological processes including anticoagulant and platelet-modulating activities. We purified the C-type lectin (BiLec) from Bothrops insularis venom and investigated its effect in the isolated kidney. BiLec was purified after two chromatographic steps; firstly, the whole venom was submitted to an HPLC molecular exclusion chromatography followed by a second purification through affinity chromatography. B. insularis lectin (BiLec) was studied as to its effect on the renal function of isolated perfused rat kidneys with the use of six Wistar rats. The concentration of 10mug/mL increased perfusion pressure (PP; control(60)=108.27+/-4.9; BiLec(60)=112.9+/-5.4 mmHg; *p<0.05) and renal vascular resistance (RVR; control(60)=5.38+/-0.51; BiLec(60)=6.01+/-0.57 mmHg; *p<0.05). The urinary flow reduced significantly at 90 and 120 min of perfusion (UF; control(120)=0.160+/-0.020; BiLec(120)=0.082+/-0.008 mL g(-1) min(-1); *p<0.05). Glomerular filtration rate (GFR; control(120)=0.697+/-0.084; BiLec(120)=0.394+/-0.063 mL g(-1) min(-1); *p<0.05) diminished only at 120 min. BiLec did not change the percentage of sodium (TNa(+)), potassium (TK(+)) and chloride tubular transport (TCl(-)). The histological alterations probably reflected direct injury on glomerular and tubular renal cells, as demonstrated by the rise in permeability of glomerular endothelial cells, revealed by the presence of a proteinaceous material in the Bowman space. We postulate that the C-type lectin B. insularis promoted its effects probably through interactions with endothelial cells or through the release of other mediators by tubular, mesangial and endothelial cells.

Human intervertebral disc cells promote nerve growth over substrata of human intervertebral disc aggrecan

STUDY DESIGN

Coculture assays of the migration and interaction of human intervertebral disc cells and chick sensory nerves on alternate substrata of collagen and aggrecan.

OBJECTIVE

To examine the effects of aggrecan on disc cell migration, how disc cells and sensory nerves interact, and whether disc cells affect previously reported inhibitory effects of aggrecan on sensory nerve growth.

SUMMARY OF BACKGROUND DATA

Human intervertebral disc aggrecan is inhibitory to sensory nerve growth in vitro, suggesting that a loss of aggrecan from the disc may have a role in the increased innervation seen in disc degeneration. Endothelial cells that appear to co-migrate with nerves into degenerated intervertebral disc express neurotrophic factors, but the effects of disc cells on nerve growth are not known.

METHODS

Human disc cells were seeded onto tissue culture plates that had been coated with type I collagen and human intervertebral disc aggrecan. Explants of chick dorsal root ganglions (DRGs) were subsequently added to the plates and sensory neurite outgrowth stimulated by the addition of nerve growth factor. Time-lapse video and fluorescence microscopy were used to examine the migration and interaction of the disc cells and sensory neurites, in the context of the different matrix substrata. The effects of disc cell conditioned medium on nerve growth were also examined.

RESULTS

Disc cells spread and migrated on collagen until they encountered the aggrecan substrata, where some cells, but not all, were repelled. In coculture, DRG neurites extended onto the collagen/disc cells until they encountered the aggrecan, where, like the disc cells, many were repelled. However, in the presence of disc cells, some neurites were able to cross onto this normally inhibitory substratum. The number of neurite crossings onto aggrecan correlated significantly with the number of disc cells present on the aggrecan. In control experiments using DRG alone, all extending neurites were repelled at the collagen/aggrecan border. Conditioned medium from disc cell cultures stimulated DRG neurite outgrowth on collagen but did not increase neurite crossing onto aggrecan substrata.

CONCLUSIONS

Human disc cells migrate across aggrecan substrata that are repellent to sensory DRG neurites. Disc cells synthesize neurotrophic factors in vitro that promote neurite outgrowth. Furthermore, the presence of disc cells in coculture with DRG partially abrogates the inhibitory effects of aggrecan on nerve growth. These findings have important implications for the regulation of nerve growth into the intervertebral disc, but whether disc cells promote nerve growth in vivo remains to be determined.

Collagen binding by the mannose receptor mediated through the fibronectin type II domain

The macrophage mannose receptor is the prototype for a family of receptors each having an extracellular region consisting of an N-terminal cysteine-rich domain related to the R-type carbohydrate-recognition domain of ricin, a fibronectin type II domain and eight to ten domains related to C-type carbohydrate-recognition domains. The mannose receptor acts as a molecular scavenger, clearing harmful glycoconjugates or micro-organisms through recognition of their defining carbohydrate structures. Cell-adhesion assays, as well as collagen-binding assays, have now been used to show that the mannose receptor can also bind collagen and that the fibronectin type II domain mediates this activity. Neither of the two types of sugar-binding domain in the receptor is involved in collagen binding. Fibroblasts expressing the mannose receptor adhere to type I, type III and type IV collagens, but not to type V collagen, and the adherence is inhibited by isolated mannose receptor fibronectin type II domain. The fibronectin type II domain shows the same specificity for collagen as the whole receptor, binding to type I, type III and type IV collagens. This is the first activity assigned to the fibronectin type II domain of the mannose receptor. The results suggest additional roles for this multifunctional receptor in mediating collagen clearance or cell-matrix adhesion.

Composition of perineuronal net extracellular matrix in rat brain: a different disaccharide composition for the net-associated proteoglycans

We developed a method to extract differentially chondroitin sulfate proteoglycans (CSPGs) that are diffusely present in the central nervous system (CNS) matrix and CSPGs that are present in the condensed matrix of perineuronal nets (PNNs). Adult rat brain was sequentially extracted with Tris-buffered saline (TBS), TBS-containing detergent, 1 m NaCl, and 6 m urea. Extracting tissue sections with these buffers showed that the diffuse and membrane-bound CSPGs were extracted in the first three buffers, but PNN-associated CSPGs remained and were only removed by 6 m urea. Most of the CSPGs were extracted to some degree with all the buffers, with neurocan, brevican, aggrecan, and versican particularly associated with the stable urea-extractable PNNs. The CSPGs in stable complexes only extractable in urea buffer are found from postnatal day 7-14 coinciding with PNN formation. Disaccharide composition analysis indicated a different glycosaminoglycan (GAG) composition for PGs strongly associated with extracellular matrix (ECM). For CS/dermatan sulfate (DS)-GAG the content of nonsulfated, 6-O-sulfated, 2,6-O-disulfated, and 4,6-O-disulfated disaccharides were higher and for heparan sulfate (HS)-GAG, the content of 6-O-sulfated, 2-N-, 6-O-disulfated, 2-O-, 2-N-disulfated, and 2-O-, 2-N-, 6-O-trisulfated disaccharides were higher in urea extract compared with other buffer extracts. Digestions with chondroitinase ABC and hyaluronidase indicated that aggrecan, versican, neurocan, brevican, and phosphacan are retained in PNNs through binding to hyaluronan (HA). A comparison of the brain and spinal cord ECM with respect to CSPGs indicated that the PNNs in both parts of the CNS have the same composition.

Refolding, purification, and characterization of human and murine RegIII proteins expressed in Escherichia coli

The regenerating (Reg) family comprises an extensive, diversified group of proteins with homology to C-type lectins. Several members of this family are highly expressed in the gastrointestinal tract under normal conditions, and often show increased expression in inflammatory bowel disease. However, little is known about Reg protein function, and the carbohydrate ligands for these proteins are poorly characterized. We report here the first expression and purification of Reg proteins using a bacterial system. Mouse RegIIIgamma and its human counterpart, HIP/PAP, were expressed in Escherichia coli, resulting in the accumulation of aggregated recombinant protein. Both proteins were renatured by arginine-assisted procedures and were further purified using cation-exchange chromatography. The identities of the purified proteins were confirmed by SDS-PAGE, N-terminal sequencing, and MALDI-TOF mass spectrometry. Size exclusion chromatography revealed that both proteins exist as monomers, and circular dichroism showed that their secondary structures exhibit a predominance of beta-strands which is typical of C-type lectins. Finally, both RegIIIgamma and human HIP/PAP bind to mannan but not to monomeric mannose, giving initial insights into their carbohydrate ligands. These studies thus provide an essential foundation for further analyses of human and mouse RegIII protein function.

Amino acid sequences and phosphorylation sites of emu and rhea eggshell C-type lectin-like proteins

Avian calcified eggshell layers contain in their organic matrix one or two C-type lectin-like proteins. Previously characterized eggshell proteins of this family are chicken ovocleidin-17 (OC-17), goose ansocalcin and ostrich struthiocalcins 1 and 2 (SCA-1, SCA-2). In this report we present the amino acid sequences of two emu (Dromaius novaehollandiae) (dromaiocalcin-1 and -2; DCA-1, DCA-2) and of two rhea (Rhea americana) (rheacalcin-1 and -2; RCA-1, RCA-2) C-type lectin-like eggshell proteins, thus doubling the data set for comparison of these major specific eggshell proteins. The ratite proteins can be divided into two groups. Group 1, comprising SCA-1, DCA-1 and RCA-1, shows by 70--77% identity of sequences, the lack of phosphorylation, and a variable number (7--9) of cysteines. Group 2, consisting of SCA-2, DCA-2 and RCA-2, shows 78--85% identical sequences, 2--3 phosphorylated serines located at almost identical sites, and contains only the common set of six conserved cysteins characteristic for this family of proteins. While goose ansocalcin fits perfectly into group 1 with a sequence identity of 63--70% to the other members, no phosphorylation, and seven cysteines, chicken OC-17 was assigned to group 2 in spite of only 42--47% sequence identity (and 37--39% to group 1) because of its two phosphorylated serines and its regular set of six cysteines. At present it remains unknown why ratites, but not goose or chicken, require two different types of C-type lectin-like proteins to construct their eggshells.

Crotacetin, a Novel Snake Venom C-Type Lectin Homolog of Convulxin, Exhibits an Unpredictable Antimicrobial Activity

Snake venom (sv) C-type lectins encompass a group of hemorrhagic toxins that are capable of interfering with blood stasis. A very well-studied svC-type lectin is the heterodimeric toxin, convulxin (CVX), from the venom of South American rattlesnake Crotalus durissus terrificus. CVX is able to activate platelets and induce their aggregation by acting via p62/GPVI collagen receptor. By using polymerase chain reaction homology screening, we have cloned several cDNA precursors of CVX subunit homologs. One of them, named crotacetin (CTC) beta-subunit, predicts a polypeptide with a topology very similar to the tridimensional conformations of other subunits of CVX-like snake toxins, as determined by computational analysis. Using gel permeation and reverse-phase high-performance liquid chromatography, CTC was purified from C. durissus venoms. CTC can be isolated from the venom of several C. durissus subspecies, but its quantitative predominance is in the venom of C. durissus cascavella. Functional analysis indicates that CTC induces platelet aggregation, and, importantly, exhibits an antimicrobial activity against Gram-positive and -negative bacteria, comparable with CVX.

Characterization and molecular cloning of dabocetin, a potent antiplatelet C-type lectin-like protein from Daboia russellii siamensis venom

A novel C-type lectin-like protein, dabocetin, was purified from Daboia russellii siamensis venom. On SDS-polyacrylamide gel electrophoresis, it showed a single band with an apparent molecular weight of 28 kDa and two distinct bands with the apparent molecular weights of 15.0 kDa and 14.5 kDa under non-reducing and reducing conditions, respectively. cDNA clones containing the coding sequences for dabocetin alpha and beta subunits were isolated and sequenced. The deduced protein sequences of both subunits were confirmed by N-terminal amino acid sequencing and trypsin-digested peptide mass fingerprinting. Dabocetin did not induce platelet aggregation in platelet-rich plasma. It also had little effect on the platelet aggregation induced by ADP, TMVA or stejnulxin. Whereas, dabocetin inhibited ristocetin-induced platelet agglutination in platelet-rich plasma in a dose-dependent manner with an IC50 value of 0.35 microM. Flow cytometry analysis showed that dabocetin significantly inhibited mAb SZ2 binding to platelet membrane glycoprotein Ib alpha, indicating that platelet membrane glycoprotein Ib is involved in the inhibitory effect of dabocetin on ristocetin-induced platelet agglutination.

A novel 25 kDa protein from the venom of Bitis arietans with similarity to C-type lectins causes fibrinogen-dependent platelet agglutination

Snake venoms affect blood coagulation and platelet functions in various ways. Venom from the Viperidae and Crotalidae family of snakes contains biologically active proteins that possess coagulant and anticoagulant activities, as well as platelet aggregating and inhibitory activities. Many of these proteins belong to the C-type lectin family. C-type lectins from viper venoms can act by prohibiting the interaction between platelet receptors, such as GPIIbIIIa and the GPIb/V/IX complex, and their ligands. We report on the purification of a novel 25 kDa protein, Ba25, from Bitis arietans with a primary structure that possesses similarity to other C-type lectins from viper venom. This protein has a profound effect on the clotting of whole blood, as well as being able to cause agglutination of platelets in platelet rich plasma without degranulation of the cells, but not of washed platelets in the absence of fibrinogen. Ba25 interacts with the platelet via the GPIb/V/IX, as well as the GPIIbIIIa receptor, and causes an increase in binding of fibrinogen to platelets. These results suggest that Ba25 may be a potent mediator of platelet-platelet interactions, and other coagulatory mechanisms.

A C-type lectin-like protein from Agkistrodon acutus venom binds to both platelet glycoprotein Ib and coagulation factor IX/factor X

Agkisacutacin, a C-type lectin-like protein (CLP) isolated from Agkistrodon acutus venom, had been previously identified as an antagonist of platelet aggregation induced by ristocetin, as well as a certain extent fibrinogenlytic activity. In this study, agkisacutacin was further purified by three-step chromatography, and its biological functions were characterized. Agkisacutacin after further purification retained the effect on ristocetin-induced, von Willebrand factor-dependent platelet aggregation, while it lost the fibrinogenlytic activity. FACS and ELISA assays showed that agkisacutacin belongs to membrane glycoprotein Ib-binding protein (GPIb-bp) for it could block and inhibit the binding of anti-GPIb antibody to GPIb. Especially, agkisacutacin exhibits anti-coagulant activity and the function as IX/X-binding protein was confirmed by PAGE and ELISA. So, agkisacutacin is the first reported CLP that binds to both platelet membrane receptors and coagulation factors.

C-type lectin-related proteins from snake venoms

C-type lectin-like proteins (CLPs) of snake venom have a variety of biological properties, acting for example as anticoagulants, procoagulants, and agonists/antagonists of platelet activation. The structural and functional studies of the first identified CLP, factor IX/factor X-binding protein, have led to an understanding how new functionally heterodimeric CLPs from monomeric C-type lectin related proteins may have evolved by 3D domain swapping, and have contributed to our understanding of the significance of magnesium ions in the blood coagulation cascade reaction. Two metallo-proteases, carinactivase and RVV-X (factor X activator of a snake venom), with C-type lectin-like domains, were isolated, characterized, and found to be useful in the study of the properties of prothrombin and coagulation factor X. There are also several unique CLPs belong to agonists and antagonists of platelet receptors, platelet glycoprotein Ib and glycoproteins Ia/IIa and VI, collagen receptors and the following CLPs that modulate platelet function. These CLPs may provide the new insights into platelet function: alboaggregin-B, echicetin, botrocetin, bitiscetin, flavocetin-A, aggretin/rhodocytin, convulxin, and agkistin.

A new C-type animal lectin isolated from Bothrops pirajai is responsible for the snake venom major effects in the isolated kidney

We investigated the biochemical and biological effects of a new C-type galactoside specific lectin termed BPL that was isolated from the snake venom of Bothrops pirajai. This lectin was purified using size exclusion HPLC followed by an immobilized lactose affinity column. The purified BPL was homogeneous by reverse phase HPLC and SDS-PAGE. We evaluated the nephrotoxicity of the whole venom of B. pirajai and its lectin. The whole venom of B. pirajai (10 microg/mL) showed similar results as those observed for BPL (3, 10 and 30 microg/mL) evaluated by the perfused rat kidney method. They caused reductions in perfusion pressure (Control120 = 110.28 +/- 3.69; BP120 = 70.70 +/- 2.40*; BPL3(120) = 113.20 +/- 4.40; BPL10(120) = 67.80 +/- 3.00*; BPL30(120) = 64.90 +/- 3.50* mmHg; *: P < 0.05), renal vascular resistance, urinary flow, glomerular filtration rate (Control90 = 0.695 +/- 0.074; BP90 = 0.142 +/- 0.032*; BPL3(90) = 0.314 +/- 0.064; BPL10(90) = 0.250 +/- 0.038*; BPL30(90) = 0.088 +/- 0.021* mLg(-1) min(-1); *: P < 0.05) and sodium (Control120 = 81.28 +/- 0.26; BP120 = 55.71 +/- 5.72*; BPL3(120) = 80.94 +/- 0.93; BPL10(120) = 65.23 +/- 1.47*; BPL30(120) = 76.03 +/- 1.70* %; *: P < 0.05), potassium and chloride tubular transport. Neither whole venom nor purified BPL induced direct vasoactive effects in perfused arteriolar mesenteric bed, and BPL did not potentiate bradykinin contraction in the ileum. We postulate that both B. pirajai and BPL promoted the same renal effects probably caused by the release of inflammatory mediators.

Molecular and Sugar-Binding Heterogeneity of C-Type Lectins from Osmerus (Spirinchus) lanceolatus Eggs

Two C-type lectins (OLLafs and OLLafl) were isolated from Osmerus (Spirinchus) lanceolatus eggs using asialofetuin-Sepharose column. OLLafs and OLLafl were eluted with 0.2 M sucrose and 0.2 M lactose from the same column, respectively. OLLafl has been estimated to be a heterodimeric protein composed of H- and L-subunit and involved C-type lectin like domain (CTLD). In this study we revealed that OLLafs was a homodimeric protein composed of L-subunit of OLLafl. Although adding EDTA diminished the hemagglutinating activity of OLLafs, the activity of OLLafl was not influenced. Recombinant lectins (rOLLafl-H and -L) and mutant lectins replaced Cys(123, 131 and 136) with Ala (mOLLafl-L(123, 131 and 136)) were established. The activity of mOLLafl-L(136) was comparable to rOLLafl-L, and rOLLafl-H was 15 times lower than rOLLafl-L. On the other hand, the activity of mOLLafl-L(123) and mOLLafl-L(131) were lower than that of rOLLafl-H. Therefore, Cys(136) may not participate in hemagglutinating activity of rOLLafl-L. In contrast, Cys(123) and Cys(131) may partially contribute this activity. Although hemagglutination inhibition profiles of rOLLafl-L, rOLLafl-H and mOLLafl-L(136) were similar, m-OLLafl-L(131)-induced hemagglutination was not inhibited by any sugars tested even at a concentration of 150 mM. Then, Cys(131) may directly contribute to the sugar-binding capacity of OLLafl. Affinities of mOLLafl-L(123) for these sugars were lower than the others. These results suggest that Cys(136) might contribute to the intermolecular disulfide bond in the rOLLafl-L dimer, and that the intramolecular disulfide bond concerning Cys(131) might important for lectin activity.

Cytotoxicity of a GalNAc-Specific C-Type Lectin CEL-I toward Various Cell Lines

We found that CEL-I was a potent cytotoxic lectin. MDCK, HeLa, and XC cells were highly sensitive to CEL-I cytotoxicity and killed in a dose-dependent manner, whereas CHO, L929, and RAW264.7 cells were relatively resistant to CEL-I, and no significant toxicity was observed up to 10 microg/ml. Among these cell lines, MDCK cells showed the highest susceptibility to CEL-I cytotoxicity. A binding study using FITC-labeled CEL-I (F-CEL-I) revealed that the amounts of bound F-CEL-I on the sensitive cell lines were evidently greater than those on the resistant cell lines, suggesting that the different susceptibility of the cell lines to CEL-I cytotoxicity is partly explained by different efficiencies of binding of CEL-I to these cell lines. Interestingly, the cytotoxicity of CEL-I toward MDCK cells was more potent than those of other lectins such as WGA, PHA-L, and Con A, even though these lectins were capable of binding to MDCK cells at comparable levels to CEL-I. Since the cytotoxicity of CEL-I was strongly inhibited by GalNAc, the binding to cell surface specific carbohydrates is essential for the CEL-I cytotoxicity. The trypan blue dye exclusion test indicated that CEL-I caused a disorder of plasma membrane integrity as a relatively early event. CEL-I failed to induce the release of carboxyfluorescein (CF) from CF-loaded MDCK cells as seen for pore-forming hemolytic isolectin CEL-III, suggesting that the primary cellular target of CEL-I may be the plasma membrane, but its action mechanism differs from that of CEL-III. Although CEL-I induced dramatic cellular morphological changes in MDCK cells, neither typical apoptotic nuclear morphological changes nor DNA fragmentation was observed in CEL-I-treated MDCK cells even after such cellular changes. Our results demonstrated that CEL-I showed a potent cytotoxic effect, especially on MDCK cells, by causing plasma membrane disorder without induction of apoptosis.

Crystallization and preliminary X-ray crystallographic analysis of agkicetin-C from Deinagkistrodon acutus venom

The crystallization and preliminary crystallographic analysis of agkicetin-C, a well known platelet glycoprotein Ib (GPIb) antagonist from the venom of Deinagkistrodon acutus found in Anhui Province, China is reported. Crystals of agkicetin-C suitable for structure determination were obtained from 1.8 M ammonium sulfate, 40 mM MES pH 6.5 with 2%(v/v) PEG 400. Interestingly, low buffer concentrations of MES seem to be necessary for crystal growth. The crystals of agkicetin-C belong to space group C2, with unit-cell parameters a = 177.5, b = 97.7, c = 106.8 A, beta = 118.5 degrees, and diffract to 2.4 A resolution. Solution of the phase problem by the molecular-replacement method shows that there are four agkicetin-C molecules in the asymmetric unit, with a VM value of 3.4 A3 Da(-1), which corresponds to a high solvent content of approximately 64%. Self-rotation function calculations show a single well defined non-crystallographic twofold axis with features that may represent additional elements of non-crystallographic symmetry.

Purification, characterization, crystallization and preliminary X-ray crystallographic analysis of two novel C-type lectin-like proteins: Aall-A and Aall-B fromDeinagkistrodon acutusvenom

Aall-A and Aall-B, two novel heterodimeric snake-venom C-type lectin-like proteins (sv-CLPs), were purified from the venom of Deinagkistrodon acutus from Anhui, China. Strikingly, both these proteins can localize on and congregate human erythrocytes, instead of aiming at the common targets of sv-CLPs such as platelet glycoproteins, von Willebrand factors, coagulant factors etc. The crystals of Aall-A belong to space group P2, with unit-cell parameters a = 105.2, b = 56.2, c = 108.7 A, beta = 100.5 degrees , and diffract to 2.0 A resolution, while the crystals of Aall-B belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 36.8, b = 56.5, c = 149.2 A, and diffract to 2.2 A resolution. To our knowledge, this is the first report of sv-CLPs with this unique function and of their preliminary crystallographic analysis.

Cloning, expression, and structural analysis of recombinant BJcuL, a c-type lectin from the Bothrops jararacussu snake venom

The lactose-binding lectin from Bothrops jararacussu venom (BJcuL) is a homodimer belonging to group VII of the c-type animal lectins. BJcuL has also been shown to serve as an interesting tool for combating tumor progression by inhibiting cancer and endothelial cell growth. However, detailed structural studies of BJcuL and its biological mechanisms of cytotoxicity are yet to be reported, perhaps because of the non-availability of recombinant proteins in necessary quantities. Intending to increase the present information about structural and consequently the understating of biological studies, the cDNA coding for BJcuL from a venom gland has been cloned and sequenced. The mature protein-coding region was amplified by PCR with specific oligonucleotides, and subcloned into the pET-15b vector to express the recombinant BJcuL in Escherichia coli BL21 (DE3). The deduced amino acid sequence exhibits a high degree of sequence identity with c-type lectins (CTLs) and c-type lectin-like domains (CTLDs). An insoluble and inactive 18.5-kDa protein was overexpressed after 1.0mM IPTG induction. The recombinant BJcuL was recovered and denatured in a buffer with 6M urea and purified on a nickel-affinity column. Protein refolding was carried out on this column, during procedure purification, followed by dialysis against CTBS and then by gel filtration for separation of the active dimmer. The refolding process of rBJcuL and the analysis of its structure were confirmed by biological assay, circular dichroism, and MALDI-TOF.

Lebectin, a novel C-type lectin from Macrovipera lebetina venom, inhibits integrin-mediated adhesion, migration and invasion of human tumour cells

The adhesion receptors of the integrin family play an essential role during tumour progression and thus represent interesting potential targets for the development of new therapeutic agents. The snake venom contains natural inhibitors of integrin-ligand interactions called disintegrins. It also contains C-type lectin proteins mainly known as modulators of platelet aggregation. In this study, we demonstrate that lebectin, a novel C-type lectin isolated from Macrovipera lebetina venom, displayed an anti-integrin activity. Lebectin inhibited the integrin-mediated attachment of various tumour cell lines to different adhesion substrata. The C-type lectin also completely blocked cell migration towards fibronectin in haptotaxis assays and prevented invasion of fibrin gels by tumour cells. In addition, lebectin proved to be a potent inhibitor of tumour cell proliferation. Although the specific integrins affected by lebectin are not identified in this study, the integrin alpha 5 beta 1 might be involved.

Isolation and characterization of a C-type lectin cDNA specifically expressed in the tip of mouthparts of the flesh fly Sarcophaga peregrina

We have isolated a novel gene, CLEM 36, of the flesh fly Sarcophaga peregrina, which shows significant homology to the C-type lectin family. CLEM 36 mRNA was transcribed excessively from the second day after eclosion only in the tip of mouthparts. Whole mount in situ hybridization showed that CLEM 36 mRNA was expressed in the C-type lectin-producing tissue (CLPT) located at the entrance of the food canal and between the labellum and haustellum. Immunoblot analysis showed that the mature form of CLEM 36 protein was synthesized in the CLPT, then secreted into saliva. Our results indicate that CLEM 36 protein may play an important role in biological defence against pathogens during the food intake of this insect.

A C-type lectin associated and translocated with cortical granules during oocyte maturation and egg fertilization in fish

Oocyte maturation and egg fertilization in both vertebrates and invertebrates are marked by orchestrated cytoplasmic translocation of secretory vesicles known as cortical granules. It is thought that such redistribution of cellular content is critical for asymmetrical cell division during early development, but the mechanism and regulation of the process is poorly understood. Here we report the identification, purification and cDNA cloning of a C-type lectin from oocytes of a freshwater fish species gibel carp (Carassius auratus gibelio). The purified protein has been demonstrated to have lectin activity and to be a Ca(2+)-dependent C-type lectin by hemagglutination activity assay. Immunocytochemistry revealed that the lectin is associated with cortical granules, gradually translocated to the cell surface during oocyte maturation, and discharged to the egg envelope upon fertilization. Interestingly, the lectin becomes phosphorylated on threonine residues upon induction of exocytosis by fertilization and returns to its original state after morula stage of embryonic development, suggesting that this posttranslational modification may represent a critical molecular switch for early embryonic development.

Ostrich (Struthio camelus) eggshell matrix contains two different C-type lectin-like proteins. Isolation, amino acid sequence, and posttranslational modifications

In contrast to chicken and goose, the ostrich calcified eggshell layer matrix contained two different C-type lectin-like proteins as major components. These proteins, named struthiocalcin-1 (SCA-1) and struthiocalcin-2 (SCA-2), were isolated and their amino acid sequence was determined. SCA-1 clearly was the ortholog of goose eggshell ansocalcin. Its amino acid sequence had the same length as that of ansocalcin (132 aa) and showed 65% sequence identity with the goose eggshell protein compared to 41% with chicken eggshell ovocleidin-17. Furthermore, as ansocalcin and unlike ovocleidin-17, it contained an additional, seventh, cysteine that was, however, located close to the C-terminus of SCA-1 and not in the N-terminal third of the sequence as in ansocalcin. SCA-2 showed features of both ansocalcin and chicken eggshell ovocleidin-17 (OC-17). Its sequence was 46% identical to that of ansocalcin and 36% identical to OC-17. It contained the same stretches of negatively charged amino acids conserved in ansocalcin and SCA-1, which are absent in OC-17. On the other hand, its length of 142 amino acids was identical to that of OC-17 and it contained only the usual set of six cysteines conserved in most C-type lectin-like proteins. The presence of three phosphorylated serines located at exactly the same region of the sequence as the two phosphoserines of OC-17 further stressed the similarity between SCA-2 and OC-17.

Convulxin binds to native, human glycoprotein Ib alpha

Convulxin (CVX), a C-type snake protein from Crotalus durissus terrificus venom, is the quintessential agonist for studies of the collagen receptor, glycoprotein VI (GPVI) and its role in platelet adhesion to collagens. In this study, CVX, purified from venom, behaves as expected, i.e. it binds to platelet GPVI and recombinant human GPVI, induces platelet aggregation and platelet prothrombinase activity, and binds uniquely to GPVI in ligand blots of SDS-denatured proteins. Nonetheless, we find that CVX has a dual specificity for both GPVI and native but not denatured human GPIb alpha. First, CVX binds to human GPIb alpha expressed on the surface of CHO cells. Second, CVX binds weakly to murine platelet GPIb alpha but more strongly to human platelet GPIb alpha, as evidenced by comparative binding to wild-type, GPVI(-/-), FcR gamma (-/-), and human GPIb transgenic mice. Third, the binding of CVX to human GPIb alpha is inhibited by soluble, recombinant human GPVI. Fourth, CVX binding to GPIb alpha is disrupted by phenylalanine substitutions at GPIb alpha tyrosine-276, tyrosine-278, and tyrosine-279, which also disrupts von Willebrand factor and alpha-thrombin binding to GPIb alpha. Fifth, CVX binding to GPIb alpha on Chinese hamster ovary cell transfectants is inhibited by function-blocking murine monoclonal anti-GPIb alpha antibodies. Lastly, CVX fails to bind to denatured GPIb alpha in detergent extracts of platelets. Three separate preparations of CVX (two purified by the authors; one obtained commercially) produced equivalent results. These results indicate that CVX exhibits dual specificity for both native GPIb alpha and GPVI. Furthermore, the binding site on GPIb alpha for CVX may be close to that for von Willebrand factor. Therefore, a contribution of GPIb alpha to CVX-induced platelet responses needs to be carefully re-evaluated.

Expression of a novel regenerating gene product, Reg IV, by high density fermentation in Pichia pastoris: production, purification, and characterization

Human regenerating (Reg) gene products are regionally expressed by gut-derived tissues, and are markedly up-regulated in cancer and in diseases characterized by mucosal injury. We recently identified Reg IV, a novel regenerating gene product that is uniquely expressed by the normal distal gastrointestinal mucosa. The function remains poorly understood due to the lack of significant purified Reg IV for biochemical and functional studies. Recombinant human Reg IV was efficiently expressed under the control of the AOX1 gene promoter in Pichia pastoris using the MutS strain KM71H. We describe the unique conditions that are required for efficient production of Reg IV protein in high density fermentation. Optimal protein expression was obtained by reduction of the fermentation temperature and addition of casamino acids as a supplemental nitrogen source and to minimize the activity of yeast produced proteases. Recombinant Reg IV protein was purified by tangential flow filtration and reverse phase chromatography. The purified protein was characterized by amino terminus sequence analysis and MALDI-TOFMS showing that the engineered protein had the expected sequence and molecular weight without secondary modification. Recombinant Reg IV was further characterized by specific monoclonal and polyclonal reagents that function for Western blot analysis and for immunolocalization studies.