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At least 19 recordsLinked to original sources
PubMed2026

LitCTL1: A novel C-type lectin involved in the mucosal and cellular immunity of the common periwinkle Littorinalittorea.

C-type lectins (CTLs) are vital pattern-recognition receptors (PRRs) that mediate innate immune responses in mollusks, yet their characterization in Caenogastropoda, the largest gastropod group, remains limited. This study characterizes LitCTL1, a novel secreted single-domain C-type lectin from the common periwinkle, Littorina littorea. The 199-amino acid polypeptide contains a conserved carbohydrate recognition domain with canonical QPD and WND motifs and is predicted to form a homodimer. Uniquely, LitCTL1 was localized in both circulating hemocytes and mucus-secreting epithelial cells of the foot, mantle, and hypobranchial gland - the first report of such dual localization for a molluscan lectin, linking systemic and mucosal defense. Expression analysis revealed that LitCTL1 is constitutively expressed in hemocytes. Functional assays with recombinant LitCTL1 demonstrated its role as a potent opsonin with hemagglutinating activity, significantly enhancing hemocyte spreading and the phagocytosis of zymosan. Genomic analysis reveals that LitCTL1 belongs to a rapidly diversifying, genus-specific expansion distinct from conserved perlucin-like lineages. These results identify LitCTL1 as a key effector molecule in both systemic and mucosal innate immunity, likely reflecting an evolutionary adaptation to the microbial challenges of the intertidal environment.

Animals↗
PubMed1991

Human surfactant protein D: SP-D contains a C-type lectin carbohydrate recognition domain.

Lung surfactant protein D (SP-D) shows calcium-dependent binding to specific saccharides, and is similar in domain structure to certain members of the calcium-dependent (C-type) lectin family. Using a degenerate oligomeric probe corresponding to a conserved peptide sequence derived from the amino-terminus of the putative carbohydrate binding domain of rat and bovine SP-D, we screened a human lung cDNA library and isolated a 1.4-kb cDNA for the human protein. The relationship of the cDNA to SP-D was established by several techniques including amino-terminal microsequencing of SP-D-derived peptides, and immunoprecipitation of translation products of transcribed mRNA with monospecific antibodies to SP-D. In addition, antibodies to a synthetic peptide derived from a predicted unique epitope within the carbohydrate recognition domain of SP-D specifically reacted with SP-D. DNA sequencing demonstrated a noncollagenous carboxy-terminal domain that is highly homologous with the carboxy-terminal globular domain of previously described C-type lectins. This domain contains all of the so-called "invariant residues," including four conserved cysteine residues, and shows high homology with the mannose-binding subfamily of C-type lectins. Sequencing also demonstrated an amino-terminal collagenous domain that contains an uninterrupted sequence of 59 Gly-X-Y triplets and that also contains the only identified consensus for asparagine-linked oligosaccharides. The studies demonstrate that SP-D is a member of the C-type lectin family, and confirm predicted structural similarities to conglutinin, SP-D, and the serum mannose binding proteins.

Amino Acid Sequence↗
PubMed2024

The Dectin-1 and Dectin-2 clusters: C-type lectin receptors with fundamental roles in immunity.

The ability of myeloid cells to recognize and differentiate endogenous or exogenous ligands rely on the presence of different transmembrane protein receptors. C-type lectin receptors (CLRs), defined by the presence of a conserved structural motif called C-type lectin-like domain (CTLD), are a crucial family of receptors involved in this process, being able to recognize a diverse range of ligands from glycans to proteins or lipids and capable of initiating an immune response. The Dectin-1 and Dectin-2 clusters involve two groups of CLRs, with genes genomically linked within the natural killer cluster of genes in both humans and mice, and all characterized by the presence of a single extracellular CTLD. Fundamental immune cell functions such as antimicrobial effector mechanisms as well as internalization and presentation of antigens are induced and/or regulated through activatory, or inhibitory signalling pathways triggered by these receptors after ligand binding. In this review, we will discuss the most recent concepts regarding expression, ligands, signaling pathways and functions of each member of the Dectin clusters of CLRs, highlighting the importance and diversity of their functions.

Lectins, C-Type↗
PubMed1992

Alpha-helical coiled-coil stalks in the low-affinity receptor for IgE (Fc epsilon RII/CD23) and related C-type lectins.

The low-affinity receptor for IgE (Fc epsilon RII/CD23) is a cell surface glycoprotein that plays a role in both cellular immunity and allergic inflammation. Its extracellular IgE-binding domain bears homology to C-type animal lectins, and the protein is, therefore, classified as a member of this superfamily. We predict that this lectin-like domain is separated from the cell membrane by an extensive region of alpha-helical coiled-coil structure, based upon sequence comparisons with tropomyosin, the archetypal alpha-helical coiled-coil structure, and detection of characteristic heptad repeats. Analysis of other receptor protein sequences identified a similar structural motif in other membrane-bound members of the C-type lectin superfamily, including the asialoglycoprotein receptor, the Kupffer cell receptor, and the B-cell differentiation antigen Lyb-2 (CD72). It appears that within the C-type lectin superfamily, there is a subfamily of structurally related membrane-bound receptor proteins that contain alpha-helical coiled-coil stalks of various lengths.

Amino Acid Sequence↗
PubMed1992

Primary structure of a protein isolated from reef shark (Carcharhinus springeri) cartilage that is similar to the mammalian C-type lectin homolog, tetranectin.

During the course of characterization of low molecular weight proteins in cartilage, we have isolated a protein from reef shark (Carcharhinus springeri) cartilage that bears a striking resemblance to the tetranectin monomer originally described by Clemmensen et al. (1986, Eur. J. Biochem. 156, 327-333). The protein was isolated by extraction of neural arch cartilage with 4 M guanidine hydrochloride, dialysis of the extract to bring the guanidine to 0.4 M (reassociating proteoglycan aggregates), followed by cesium chloride density gradient removal of the proteoglycans. The amino acid sequence had 166 amino acids and a calculated molecular weight of 18,430. The shark protein was 45% identical to human tetranectin, indicating that it was in the family of mammalian C-type lectins and that it was likely to be a shark analog of human tetranectin. The function of tetranectin is unknown; it was originally isolated by virtue of its affinity for the kringle-4 domain of plasminogen. Sequence comparison of human tetranectin and the shark-derived protein gives clues to potentially important regions of the molecule.

Amino Acid Sequence↗
PubMed1992

Sequence and expression of a membrane-associated C-type lectin that exhibits CD4-independent binding of human immunodeficiency virus envelope glycoprotein gp120.

The binding of the human immunodeficiency virus (HIV) envelope glycoprotein gp120 to the cell surface receptor CD4 has been considered a primary determinant of viral tropism. A number of cell types, however, can be infected by the virus, or bind gp120, in the absence of CD4 expression. Human placenta was identified as a tissue that binds gp120 in a CD4-independent manner. A placental cDNA library was screened by expression cloning and a cDNA (clone 11) encoding a gp120-binding protein unrelated to CD4 was isolated. The 1.3-kilobase cDNA predicts a protein of 404 amino acids with a calculated M(r) of 45,775 and organized into three domains: an N-terminal cytoplasmic and hydrophobic region, a set of seven complete and one incomplete tandem repeat, and a C-terminal domain with homology to C-type (calcium-dependent) lectins. A type II membrane orientation (N-terminal cytoplasmic) is predicted both by the cDNA sequence and by the reactivity of C-terminal peptide-specific antiserum with the surface of clone 11 transfected cells. Native and recombinant gp120 and whole virus bind transfected cells. gp120 binding is high affinity (kd, 1.3-1.6 nM) and inhibited by mannan, D-mannose, and L-fucose; once bound, gp120 is internalized rapidly. Collectively, these data demonstrate that the gp120-binding protein is a membrane-associated mannose-binding lectin. Proteins of this type may play an important role in the CD4-independent association of HIV with cells.

Amino Acid Sequence↗
PubMed1992

The concentration of the C-type lectin, mannan-binding protein, in human plasma increases during an acute phase response.

Two ELISAs for estimating mannan-binding protein (MBP) were constructed and the concentration of MBP in plasma was followed in patients undergoing major surgery and in patients having a malarial attack. In both cases increases of MBP in the plasma were observed. The relative increase and the kinetics varied from person to person. The concentration of MBP increased between 1.5- and three-fold following surgery. In some patients an increase was seen at day 1 whereas in others the increase was not observed until days 3-9. In the malaria patients an increased level of MBP was maintained during 30 days of treatment with chloroquine. The relative increase in MBP was independent of the presurgery or premalaria levels.

Acute-Phase Reaction↗
PubMed1992

Tissue localization of conglutinin, a bovine C-type lectin.

The distribution of bovine conglutinin (BK) in sections of frozen bovine tissues was studied by the indirect immunoperoxidase technique using a monospecific rabbit anti-BK antibody. BK was found in the cytoplasma of all hepatocytes, indicating that the liver is a major site of synthesis of BK. In the germinal centres of the spleen, tonsils and lymph nodes the anti-BK staining was restricted to a population of cells with a distribution and morphology characteristic of follicular dendritic cells. Macrophages in lung and thymus, and glia cells in cerebrum, revealed a granular staining reaction within the cytoplasma. Endothelial cells of blood vessels reacted with anti-BK. The intensity of this reaction varied greatly between the organs, the most pronounced reaction being seen in the glomeruli of the kidney, and in the capillary sinusoides of the cortex of the adrenal gland. The high endothelial venules of lymph nodes and tonsils were also stained. These findings suggest that BK, which until now has been described only as a circulating molecule, may exhibit a biological function within the BK-positive tissues.

Adrenal Cortex↗
PubMedDate not supplied

Biochemical and ultrastructural studies of the C-type lectin bovine conglutinin.

The aim of this study was to correlate the supramolecular organization of conglutinin (BK) with its primary and tertiary structure and to gain more knowledge of functionally important regions of the molecule. BK analyzed by SDS-PAGE under standard reducing conditions (40 mM DTT) showed a major band at 43 kDa and weaker bands at 86 and 180 kDa. In contrast, reduction with 6-50 mM L-cysteine resulted in 37-kDa subunits indicating the presence of intrachain disulfide bonds within this subunit. Hydroxylamine treatment indicated presence of ester bonds in the 86- and 180-kDa subunits. Collagenase digestion and SDS-PAGE under reducing and nonreducing conditions resulted in bands of 20 and 15 kDa, respectively, indicating the presence of intrachain, rather than interchain, disulfide bonds in the carboxy terminus. Deglycosylation and glycan differentiation analysis of BK revealed the presence of O-linked glycans of GalNAc and alpha (2-3) linked sialic acid type, whereas no N-linked glycans were demonstrated. Binding experiments with GlcNAc-gold suggested that multivalency is required for carbohydrate binding to BK. Electron microscopy showed mostly tetramers, 96 nm in diameter, but also mono-, di-, and trimers were seen. The tetramers consisted of 40-nm strands, each with a peripheral globular head composed of subunits and connected to a common central lobe built from four ring-formed structures. The strands occasionally showed two bends, one close to the central lobe and another 25 nm from the lobe. These bends most likely correspond to the interrupted Gly-Xaa-Yaa repeats at residues 38 and 123.

Amino Acid Sequence↗
PubMed2025

Venomics of the Arabian saw-scaled viper (Echis coloratus) through transcriptome-guided proteomics and in vitro functional profiling.

The Arabian saw-scaled viper (Echis coloratus) is among the snakes of highest medical relevance in the Middle East and North Africa. However, to date, its venom has been investigated in a very limited number of studies, and much remains unknown regarding its compositional and functional properties. By integrating proteotranscriptomics with bioactivity profiling, we present a comprehensive transcriptome-level catalogue of E. coloratus venom components and their associated biological activities. Our analysis identified 183 venom components belonging to 17 distinct protein families. Relative toxin abundances revealed that 92% of the venom proteome is composed of C-type lectin and C-type lectin-related protein (CTL), L-amino acid oxidase (LAAO), phospholipase A2 (PLA2), snake venom serine protease (SVSP), and snake venom metalloproteinase (SVMP), with CTL and PLA2 alone accounting for 73% of the total composition. Bioassays targeting key aspects of viperid envenomation demonstrated potent protease and PLA2 activity in a concentration-dependent manner. In contrast, Factor Xa-like, plasmin-like, and haemolytic activities were negligible. Marked cytotoxicity was observed at the highest concentration tested (i.e., 25 μg/ml) in the mammalian cell lines MDCK II and Calu-3, whereas cytotoxic effects were minimal at lower concentrations. These findings highlight the complexity and potency of E. coloratus venom, and provide a valuable foundation for improving our understanding of envenomation caused by this species.

Animals↗
PubMed1991

Determination of the minimum carbohydrate-recognition domain in two C-type animal lectins.

Comparison of the primary structures of numerous Ca(2+)-dependent animal lectins reveals the presence of a common sequence motif which has been suggested to form the carbohydrate-recognition domain in these proteins. The extent of the functional carbohydrate-recognition domains in two rat C-type lectins, mannose-binding protein A and the major subunit of the asialoglycoprotein receptor (rat hepatic lectin 1), has been defined by expressing truncated fragments of the proteins in an in vitro transcription and translation system. The shortest fully functional fragments constitute the COOH-terminal 120 amino acids of mannose-binding protein A and 135 amino acids of rat hepatic lectin 1. These segments correspond closely to protease-resistant protein cores which can be isolated from the native lectins. The NH2-terminal boundary of each minimum carbohydrate-recognition domain falls near the site of an intron in the corresponding gene.

Amino Acid Sequence↗
PubMed1991

cDNA cloning of mouse NKR-P1 and genetic linkage with LY-49. Identification of a natural killer cell gene complex on mouse chromosome 6.

NK cells lyse tumor cells and virally infected cells, but the molecular basis for this phenomenon has not been defined. A mAb specific for the rat cell surface molecule, NKR-P1, stimulates rat NK cell lytic activity and is reactive with all rat NK cells, suggesting that this molecule may play a significant role in NK cell function. We have previously described another NK cell-specific Ag, Ly-49, that belongs to a family of cross-hybridizing genes on distal mouse chromosome 6. The rat NKR-P1 Ag shares several features with the mouse Ly-49 Ag, including selective cell surface expression on NK cells, homology to the C-type lectins, expression as a type II integral membrane protein, and disulfide-linked homodimeric structure. To further examine the relationship of NKR-P1 to Ly-49, we have cloned the cDNA encoding a mouse homologue of NKR-P1 (mNKR-P1). The mouse and rat NKR-P1-deduced polypeptide sequences are highly conserved, suggesting a similar tertiary structure. By examination of DNA from informative recombinant inbred mice with Southern blot analysis, we have determined that mNKR-P1 is encoded by a distinct gene that is genetically linked to the Ly-49 locus, lying within 0.5 centi-Morgan (cM) of Ly-49. Although the deduced amino acid sequences of mNKR-P1 and Ly-49 reveal that these proteins are structurally similar, they are only 24% identical at the amino acid level and the cDNA sequences do not demonstrate significant nucleotide homology. Our studies suggest that we have identified a region on mouse chromosome 6 that includes distinct NK-specific genes that encode structurally related proteins (type II integral membrane proteins, C-type lectin super-gene family) but which demonstrate considerable heterogeneity. We have termed this genetic region the NK complex.

Amino Acid Sequence↗
PubMed1992

Coagulation factor X activating enzyme from Russell's viper venom (RVV-X). A novel metalloproteinase with disintegrin (platelet aggregation inhibitor)-like and C-type lectin-like domains.

We determined the complete amino acid sequence of RVV-X, the blood coagulation factor X activating enzyme, isolated from Russell's viper venom and studied structure-function relationships. RVV-X (M(r) 79,000) consists of a disulfide-bonded two-chain glycoprotein with a heavy chain of M(r) 59,000 and a light chain of heterogeneous M(r) 18,000 (LC1) and 21,000 (LC2). These chains were separated after reduction and S-pyridylethylation, and the isolated major component LC1 was used for sequence analysis. The heavy chain consists of 427 residues containing four asparagine-linked oligosaccharides, and its entire sequence was similar to that of the high molecular mass hemorrhagic protein, HR1B, isolated from the venom of Trimere-surus flavoviridis. The heavy chain contains three distinct domains, metalloproteinase, disintegrin (platelet aggregation inhibitor)-like and unknown cysteine-rich domains. On the other hand, light chain LC1 consists of 123 amino acid residues containing one asparagine-linked oligosaccharide and shows sequence homology similar to that found in the so-called C-type (Ca(2+)-dependent) lectins. Therefore, RVV-X is a novel metalloproteinase containing a mosaic structure with distintegrin-like, cysteine-rich, and C-type lectin-like domains. RVV-X potently inhibits collagen- and ADP-stimulated platelet aggregations, probably via its distintegrin-like domain, although this domain does not contain the Arg-Gly-Asp sequence which is conserved in various venom distintegrins and which is thought to be one of the interaction sites for platelet integrins. Our findings also indicate that snake venom factor IX/factor X-binding protein with a C-type lectin structure (Atoda, H., Hyuga, M., and Morita, T. (1991) J. Biol. Chem. 266, 14903-14911) inhibits RVV-X-catalyzed factor X activation; hence, the light chain of RVV-X probably participates in recognizing some portion of the zymogen factor X.

Amino Acid Sequence↗
PubMed1991

Primary structure of bovine conglutinin, a member of the C-type animal lectin family.

We report the complete amino acid sequence of bovine conglutinin obtained by structural characterization of peptides derived from the protein by various chemical and enzymatic fragmentation methods. The protein consists of 351 amino acid residues including 55 apparent Gly-X-Y repeats with two interruptions. This 171-residue-long collagenous domain separates a short noncollagenous NH2-terminal region of 25 residues from the 155-residue-long globular COOH terminus revealing the structural relation of conglutinin with mannose-binding proteins, pulmonary surfactant-associated proteins, and a complement component C1q. Eight hydroxylysine residues were found in the collagenous domain. All of these hydroxylysine residues which occupy a Y position in a Gly-X-Y triplet are possible glycosylation sites since no phenylthiohydantoin amino acid was identified in automated Edman degradation cycles corresponding to these sites. The noncollagenous COOH domain of conglutinin, on the other hand, contains a carbohydrate recognition domain which shares substantial sequence homology with C-type animal lectins. Conglutinin has the greatest sequence similarity with mannose-binding proteins and pulmonary surfactant-associated proteins.

Amino Acid Sequence↗
PubMed2026

Profiling Dectin-2-Positive Tumor-Associated Macrophages Across Human Cancers by Immunohistochemistry.

PURPOSE: To characterize the prevalence and distribution of Dectin-2-positive macrophages across human tumors and develop a research immunohistochemistry (IHC) assay to assess Dectin-2 in cancer tissues. MATERIALS AND METHODS: C-type lectin domain family 6 member A (CLEC6A), the gene encoding Dectin-2, was evaluated across 38 tumor types using The Cancer Genome Atlas. A fit-for-purpose Dectin-2 IHC assay was developed using a monoclonal antibody selected from screening 11 anti-Dectin-2 antibodies. Assay performance was supported by Dectin-2-expressing and parental cell line controls, macrophage-associated staining patterns, and comparison with an orthogonal CLEC6A in situ hybridization method using RNAscope. Dectin-2 expression was assessed in tissue microarrays (n = 553 samples) across 6 cancer types and whole tissue sections (n = 137) across 7 cancer types. RESULTS: The Cancer Genome Atlas analysis identified enriched CLEC6A expression in several tumor types, including non-small cell lung cancer (NSCLC), triple-negative breast cancer (TNBC), and subsets of head and neck cancer (HNC) and colorectal cancer (CRC). By IHC, Dectin-2-positive macrophages were detected across tumor types, with notable heterogeneity within and across cancer types. In tissue microarrays, NSCLC showed the highest frequency of Dectin-2-positive macrophage infiltration, with 38% of cases with staining ≥1% of tumor area. Whole tissue section analysis confirmed and expanded these findings, with ≥50% of NSCLC, melanoma, HNC, TNBC, and CRC samples showing Dectin-2-positive macrophages in ≥1% tumor area. CONCLUSIONS: Dectin-2 expression was observed in subsets of tumor-associated macrophages across multiple human cancers, with relatively enriched expression in NSCLC, melanoma, HNC, TNBC, and CRC. To our knowledge, this study represents the first broad protein-level characterization of Dectin-2 across multiple human tumor types, identifies cancers with relatively enriched Dectin-2-positive macrophage infiltration, and provides a foundation for future translational studies of Dectin-2-targeted therapies.

Humans↗
PubMed1991

Cell adhesive activity of two animal lectins through different recognition mechanisms.

Cell adhesive activity of two animal lectins, frog (Rana catesbeiana) S-type 14K lectin and echinoidin (a C-type lectin from sea urchin plasma), was studied with human rhabdomyosarcoma (RD) cells. RD cells attached to and spread on plastic plates coated with each lectin. Cell adhesion by the frog lectin was completely inhibited by the addition of lactose or asialofetuin glycopeptide. Echinoidin-induced cell adhesion was only inhibited by peptide GRGDS. Since echinoidin is known to contain an RGD-sequence, our results clearly indicate that this sequence is active as the cell adhesive signal. These results suggest that some of the animal lectins may function as a cell adhesive molecule rather than using the carbohydrate-recognition mechanism.

Amino Acid Sequence↗
PubMed1992

[Membrane binding and soluble lectins in higher organisms].

Lectins defined as proteins other than enzymes and antibodies that possess binding sites for specific carbohydrate sequences, are associated with the cell surface, the cytoplasm, the nucleus, extracellular matrices and body fluids, and are involved in molecular recognition, trafficking of glycoproteins and tissue organisation. Animal lectins are classified into two main groups: the C-type and the S-type lectins, characterised by sequence homology, solubility, sugar specificity, distribution, developmental regulation, calcium-dependency and reducing agents-dependency for their saccharide binding activity. Under SANU Projects supervised by Academician Milovan Jovanović, lectin types C and S were investigated. Special emphasis was placed on asialoglycoprotein receptor of rat hepatocytes, soluble beta-galactoside-binding protein of human placenta and hepatic nuclear lectins. The results of this work are presented and discussed hereinafter.

Animals↗