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PubMed2002

The mannan-binding lectin-associated serine proteases (MASPs) and MAp19: four components of the lectin pathway activation complex encoded by two genes.

Mannan-binding lectin (MBL) and ficolins (L-ficolin and H-ficolin) initiate the lectin pathway of complement activation upon binding to microbial carbohydrates. The activation is mediated by associated serine proteases, termed MASPs, since they were discovered as MBL-associated serine proteases. The MASP family comprises three serine proteases, MASP-1, MASP-2 and MASP-3 and a non-enzymatic protein, MAp19. The MASPs show identical domain structure, shared also with C1r and C1s. MASP-1 and MASP-3 are alternative splice products of a single gene, MASP1/3, and have identical A chains, whereas they have individual B chains, encompassing the serine protease domain. MASP2 and MAp19 are alternative splice products of the MASP-2 gene, with MAp19 consisting of the first two domains of MASP-2 plus additional four amino acid residues. MASP-2 is the protease responsible for activating C4 and C2 to generate the C3 convertase, C4bC2b. The biological function of the remaining three proteins has not yet been resolved.

Animals↗
PubMed1991

The endogenous lectin cerebellar soluble lectin and its ligands in central nervous system myelin of myelin-deficient (mld) mutant mice.

The myelin-deficient (mld) mutation is autosomal recessive mutation in the murine CNS exhibiting severe hypomyelination. The primary defect results in a drastic reduction of myelin basic protein synthesis caused by a duplication of the myelin basic protein gene with partial inversion of the upstream gene copy. The severe deficit of myelin basic protein is responsible for the absence of the major dense line but cannot explain the heterogeneity of myelin compaction found in mld. We have tested the hypothesis that the endogenous cerebellar soluble lectin (CSL) and/or its endogenous glycoprotein ligands could be involved in myelin abnormalities in the dysmyelinating mutant, mld. Immunocytochemical and immunoblotting techniques showed that the CSL level was not reduced significantly in the mld mutant. Furthermore, two ligands of CSL, the myelin-associated glycoprotein and an axonal glycoprotein, with a relative molecular mass of 31 kDa, were not decreased in level in the purified myelin fraction isolated from mld mice. In contrast, three minor glycoprotein ligands of CSL of relative molecular mass of 23, 18, and 16 kDa were greatly reduced in content. The reduced concentration of these low-molecular-mass glycoproteins in mld myelin suggests that they are constituents of compact myelin. Furthermore, the observation that CSL is specifically localized in vivo in regions where mld myelin is more compact and absent from regions devoid of myelin compaction may suggest that the endogenous CSL lectin, as well as its minor glycoprotein ligands, plays a role in the stabilization of the myelin sheath.

Animals↗
PubMed1992

Endogenous lectin cerebellar soluble lectin involved in myelination is absent from nonmyelinating Schwann cells.

In the sciatic nerve, two major classes of Schwann cells are present which differ in their capability to produce myelin. Myelinating Schwann cells surround most of the axons with the formation of a typical myelin sheath. Nonmyelinating Schwann cells serve to insulate individual axons without formation of myelin. These dissimilarities between the two types of Schwann cells provided an interesting model for studying mechanisms underlying myelination and the formation of contacts between axons and myelinating cells. It is demonstrated here that the endogenous lectin cerebellar soluble lectin (CSL), implicated in myelin stabilization and in formation of contact between axon and myelinating cells in the CNS and in the sciatic nerve, is undetectable in non-myelinating Schwann cells. In contrast, most axons surrounded by these cells contained the major axonal glycoprotein ligand of CSL, a 31-kDa glycoprotein which is present in large amounts. The possible relationship between the presence of CSL in Schwann cells and their capacity to interact with axons and to produce myelin are discussed.

Animals↗
PubMed1998

Lectin ligands: new insights into their conformations and their dynamic behavior and the discovery of conformer selection by lectins.

The mysteries of the functions of complex glycoconjugates have enthralled scientists over decades. Theoretical considerations have ascribed an enormous capacity to store information to oligosaccharides. In the interplay with lectins sugar-code words of complex carbohydrate structures can be deciphered. To capitalize on knowledge about this type of molecular recognition for rational marker/drug design, the intimate details of the recognition process must be delineated. To this aim the required approach is garnered from several fields, profiting from advances primarily in X-ray crystallography, nuclear magnetic resonance spectroscopy and computational calculations encompassing molecular mechanics, molecular dynamics and homology modeling. Collectively considered, the results force us to jettison the preconception of a rigid ligand structure. On the contrary, a carbohydrate ligand may move rather freely between two or even more low-energy positions, affording the basis for conformer selection by a lectin. By an exemplary illustration of the interdisciplinary approach including up-to-date refinements in carbohydrate modeling it is underscored why this combination is considered to show promise of fostering innovative strategies in rational marker/drug design.

Crystallography↗
PubMed1993

Lectin-binding glycoconjugates in the tongues of the rat and guinea pig as revealed by lectin-gold-silver methods.

Lectin-gold-silver (LT-G-S) procedures using two lectins (RCA-I and Con A) were applied to appropriately prepared paraffin sections of tongues in the rat and guinea pig. In the lingual mucous membranes of the rat and guinea pig, positive RCA-I-G-S and Con A-G-S reactions were obtained in the intercellular spaces and the cytoplasm of epithelial cells of the basal and intermediate layers respectively. Likewise, the LT (RCA-I and Con A)-G-S techniques gave rise to varying intensities of positive reactions in the serous and mucous gland acini, nerve and muscle fiber bundles and connective tissue elements. The results obtained in the present study indicate that in the rat and guinea pig tongues the histologic structures mentioned contain varying amounts of beta-D-galactose and alpha-D-mannose or alpha-D-glucose residues of glycoconjugates, and that such histochemical properties of some of the lingual structures can be correlated with their possible histophysiological functions.

Animals↗
PubMed2003

Origin of mannose-binding lectin-associated serine protease (MASP)-1 and MASP-3 involved in the lectin complement pathway traced back to the invertebrate, amphioxus.

Mannose-binding lectin-associated serine proteases (MASPs) are involved in complement activation through the lectin pathway. To elucidate the phylogenetic origin of MASP and a primordial complement system, we cloned two MASP cDNAs from amphioxus (Branchiostoma belcheri) of the cephalochordates, considered to be the closest relative of vertebrates. The two sequences, orthologues of mammalian MASP-1 and MASP-3, were produced by alternative processing of RNA from a single gene consisting of a common H chain-encoding region and two L chain-encoding regions, a structure which is similar to that of the human MASP1/3 gene. We also isolated two MASP genes from the ascidian Halocynthia roretzi (urochordates) and found that each of them consists simply of an H chain-encoding region and a single L chain-encoding region. The difference in structure between the ascidian MASP genes and the amphioxus/mammalian MASP genes suggests that a prototype gene was converted to the MASP1/3-type gene possessing two L chain-encoding regions at an early stage of evolution before the divergence of amphioxus. This conclusion is supported by the presence of MASP-1 and MASP-3 homologues in almost all vertebrates, as demonstrated by the cloning of novel cDNA sequences representing lamprey (cyclostomes) MASP-1 and Xenopus MASP-3. The ancient origin of MASP-1 and MASP-3 suggests that they have crucial functions common to all species which emerged after cephalochordates.

Amino Acid Sequence↗
PubMed1987

Differentiation of peanut lectin positive suppressor T-cells from peanut lectin negative precursors in bovine cells by 12-O-tetradecanoylphorbol-13-acetate.

Although 12-O-tetradecanoylphorbol-13-acetate (TPA) can synergize with lectins to enhance lymphocyte proliferation, pretreatment of lymphocytes with TPA decreases their response. Pretreatment also inhibits the response to allogeneic cells in the mixed lymphocyte culture. In this study we determined that at least part of this inhibition was due to the generation of T-lymphocytes with the ability to suppress proliferation in vitro. By using populations enriched in lymphocytes or macrophages we determined that the interaction of TPA with lymphocytes, but not macrophages, was required to mediate the suppression. The number of macrophages present in culture (range, 0.5-10%) was irrelevant to the generation of inhibitory activity. Moreover, the TPA-induced suppressor activity copurified with T-cells. Furthermore, when peanut lectin (agglutinin) (PNA) was used to separate T-cells after treatment with TPA, essentially all of the activity copurified with the PNA positive cells. When PNA separations were carried out before treatment with TPA, the suppressor activity arose from the PNA negative fraction. Therefore, TPA appeared to cause phenotypically PNA negative T-cells to gain the PNA positive marker, as well as to function as suppressor cells in vitro. Suppressor activity was also found in the culture medium. Thus the suppression observed may be mediated through a soluble factor released by the TPA-treated cells. Although the suppressor cell activity induced by TPA can only partially account for its in vitro inhibition of lymphocyte proliferation, the development of suppressor cells merits further study with respect to lymphocyte phenotypic and functional differentiation. The results also suggest the possibility that similar processes could occur in vivo, possibly during the course of tumor promotion.

Animals↗
PubMed1996

Properties of Ca++ release induced by puff adder lectin, a novel lectin from the snake Bitis arietans, in sarcoplasmic reticulum.

Puff adder lectin (PAL), a novel lectin venom purified from Bitis arietans, induced Ca++ release from the heavy fraction (HSR) but not from the light fraction of skeletal muscle sarcoplasmic reticulum with EC50 congruent to 10 microM. The potency of PAL was approximately 200-fold higher than that of caffeine. The bell-shaped profile of Ca++ dependence for PAL was almost the same as that for myotoxin a (MYTX), a peptide Ca++ releaser, but was different from that for caffeine. Typical blockers of Ca++ release channels, such as Mg+2, procaine, ruthenium red and ryanodine, markedly reduced PAL-induced Ca++ release from HSR. Interestingly, PAL inhibited 125I-MYTX binding to HSR with IC50 approximately equal to 20 microM. Scatchard analysis revealed that the mode of inhibition by PAL was noncompetitive, which suggests that PAL binds to a different site from that of MYTX. PAL did not affect 3H-ryanodine binding to HSR. These results suggest that PAL binds to a different site from that of MYTX to cause Ca++ release from HSR with novel properties.

Animals↗
PubMed1987

Differences in expression between two seed lectin alleles obtained from normal and lectin-deficient beans are maintained in transgenic tobacco.

Using Agrobacterium-mediated transformation, two genes for phytohemagglutinin-L (PHA-L), the lectin seed protein of the common bean Phaseolus vulgaris, were stably integrated into the tobacco genome. The two alleles for PHA-L, dlec2 and pdlec2, were obtained from a normal cultivar (Greensleeves) and a lectin-deficient cultivar (Pinto) respectively. In the bean embryos, the expression of dlec2 is 30 times greater than the expression of pdlec2. In the dlec2-transformed tobacco, PHA-L accumulated specifically in the seeds at the same stages as the tobacco seed storage proteins and was degraded after germination. PHA-L was found in the embryo, and at a 5-7 times lower concentration in the endosperm tissue of the mature tobacco seeds. No PHA could be detected in other parts of the plants. We conclude that the signals for temporal and spatial regulation of the dlec2 gene are present in the DNA fragment used for transformation. Transformation with the second PHA-L allele pdlec2 from the cultivar Pinto caused the accumulation of about 50 times less PHA-L in tobacco seeds when compared to dlec2. We conclude from analyzing the 5' sequences of dlec2 and Pdlec2 that the low expression phenotype of the Pdlec2 allele could be due to the absence or mutation of a cis-acting element carried by the dlec2 fragment.

Journal Article↗
PubMed1980

Lectin immuno tests: quantitation and titration of antigens and antibodies using lectin-antibody conjugates.

We have investigated the possibility of using lectin-antibody conjugates as general reagents in immunological procedures requiring a labeled antigen or antibody. Using these conjugates, labeling is achieved through saccharide binding sites of lectins which operate as acceptors for glycoconjugate marker substances added secondarily. Marker substances used in this work were enzymes, radioactively labeled glycoconjugates and erythrocytes, but other markers can also be used. Using the first two markers, antigens and antibodies were determined with accuracy and sensitivity equal to those of conventional enzyme or radioimmunoassays. Using erythrocytes as a marker, a simple erythro-adsorption procedure, possibly followed by hemolysis, has been developed which allowed the titration of antigens and antibodies to be carried out with a sensitivity at least equal to enzyme or radioimmunoassays.

Animals↗
PubMed2006

Improvement of an enzyme linked lectin assay to determine recombinant mistletoe lectin I.

Extracts from Viscum album leaves, with mistletoe lectin I (ML I) as the main therapeutic agent, are commonly used as an immunomodulating adjuvat in tumour therapy. Because of its popularity against cancer and the possibility for a better standardisation a recombinant ML I (rML I) was developed by Eck et al. To improve the sensitivity of an already established enzyme linked lectin assay (ELLA) for rML I human haptoglobins with different phenotypes (1.1, 2.1 and 2.2) are used to replace asialofetuin as matrix. To determine the carbohydrate binding specificity of the tested glycoproteins the ELLA was realised in the presence of the competitive carbohydrate beta-d-lactose. It could be shown that using haptoglobin phenotype 1.1 instead of asialofetuin improved the test results markedly. Both, the limit of detection and the limit of quantitation were decreased by an order of magnitude. However, this positive result was obviously accompanied by a loss in specificity of the test. The specificity of asialofetuin for rML I is almost six-fold higher than for the tested haptoglobins. Thus, in cases where high specificity and less sensitivity values for rML I is required the ELLA should still be run with asialofetuin as binding partner.

Antineoplastic Agents, Phytogenic↗
PubMed2001

The human gene for mannan-binding lectin-associated serine protease-2 (MASP-2), the effector component of the lectin route of complement activation, is part of a tightly linked gene cluster on chromosome 1p36.2-3.

The proteases of the lectin pathway of complement activation, MASP-1 and MASP-2, are encoded by two separate genes. The MASP1 gene is located on chromosome 3q27, the MASP2 gene on chromosome 1p36.23-31. The genes for the classical complement activation pathway proteases, C1r and C1s, are linked on chromosome 12p13. We have shown that the MASP2 gene encodes two gene products, the 76 kDa MASP-2 serine protease and a plasma protein of 19 kDa, termed MAp19 or sMAP. Both gene products are components of the lectin pathway activation complex. We present the complete primary structure of the human MASP2 gene and the tight cluster that this locus forms with non-complement genes. A comparison of the MASP2 gene with the previously characterised C1s gene revealed identical positions of introns separating orthologous coding sequences, underlining the hypothesis that the C1s and MASP2 genes arose by exon shuffling from one ancestral gene.

Base Sequence↗
PubMed1988

The function of Ia+ dendritic cells and Ia- dendritic cell precursors in thymocyte mitogenesis to lectin and lectin plus interleukin 1.

The response of thymocytes to lectin is a standard tissue culture model for identifying cytokines such as IL-1 that are required for thymocyte mitogenesis. To study accessory cell requirements for these responses, it was necessary to deplete endogenous accessory cells with two techniques: anti-Ia and complement, and passage over nylon wool. Proliferation to Con A was then restored with 0.1-0.3% exogenous splenic dendritic cells, or 30-fold higher levels of peritoneal macrophages. The "costimulatory" action of IL-1, whereby responses to lectin were enhanced 3-10-fold, required the presence of dendritic cells. This effect of IL-1 could be reproduced by culturing the dendritic cells for 12 h in 1 U/ml human or murine rIL-1 alpha before addition to the thymocyte proliferation assay. The function of IL-1-treated dendritic cells was not blocked by a neutralizing anti-IL-1 antibody. The endogenous population of thymic accessory cells was partially characterized. A trace (0.1-0.3%) fraction of Ia+, Ig-, plastic nonadherent dendritic cells was visualized and enriched to a level of 1-10% by depleting CD4+,CD8+, and Ig+ lymphocytes. When this double-negative population was cultured with IL-1 and washed, the treated thymic dendritic cells were 10-fold more active as accessory cells. When the CD4-,CD8-, Ig- populations were depleted of dendritic cells with anti-Ia and complement, the subsequent addition of IL-1 had a second effect. Ia+ dendritic cells redeveloped over a 2-d interval, and they exhibited the same properties as resident dendritic cells in thymus and spleen. The majority were lysed by 33D1 anti-dendritic cell mAb and complement, lacked Fc receptors, and acted as powerful stimulators of the MLR and Con A mitogenesis. The development of dendritic cells did not occur with IL-2, -3, -4 or granulocyte/macrophage colony-stimulating factor or in nylon-nonadherent populations. The IL-1-dependent, Ia- precursor was not detectable in bone marrow. These results begin to analyze the endogenous accessory function of the thymus in culture. Dendritic cells actively stimulate thymocyte mitogenesis. The mitogenic action of IL-1 involves effects on resident Ia+ dendritic cells as well as a new population of thymic, Ia- precursors.

Animals↗
PubMed1981

Human seminal lectin. II. Properties of a lectin like factor in the human seminal plasma.

A lectin like haemagglutinin (Human Seminal Lectin - HSL) is present in human seminal plasma. Partial purification and characterization of HSL has been achieved. HSL was shown to be almost completely inactivated at 100 degree C within 15 min. HSL was stable within a pH range of 5 to 10 for one hour, was resistant to trypsin, mercaptoethanol and dithiothreitol and has a molecular weight of about 57 000 daltons and an iso-electric point of about 6.8. HSL activity did not depend on either the incubation temperature or on the availability of free divalent cations such as Ca++,Mg++,or Mn++.

Chromatography, Gel↗
PubMed1992

The lectin gene family of Ricinus communis: cloning of a functional ricin gene and three lectin pseudogenes.

Molecular hybridisation using a ricin cDNA probe has revealed that the ricin/Ricinus communis agglutinin (RCA) multigene family is composed of approximately eight members. Several genomic clones containing preproricin and preproricin-like sequences have been isolated. Partial analysis of three different genomic clones by DNA sequencing and ribonuclease protection has indicated that at least three members of the lectin gene family are non-functional. None of the original seventeen positive clones isolated appears to contain a Ricinus communis agglutinin (RCA) gene. One gene member analysed (pCBG3H1) represents a functional ricin gene similar in coding sequence to the published cDNA sequence and possesses typical eukaryotic consensus sequences and seed-specific elements within the flanking sequences. Investigation at the transcriptional level of the expression pattern of this gene revealed that mRNA accumulates during the post-testa stages of seed development. The pattern of accumulation of steady-state transcripts correlates closely with that previously observed at the protein and translatable RNA levels.

Amino Acid Sequence↗
PubMed1987

Quantitative determination of the lectin binding capacity of small intestinal brush-border membrane. An enzyme linked lectin sorbent assay (ELLSA).

A test to determine quantitatively the lectin binding sites in brush-border membranes has been developed. Highly purified bovine small intestinal brush-border membranes were prepared, and subsequently coated directly to the bottom of a microtiter plate. Soybean agglutinin conjugated with peroxidase was coupled to its binding sites in the brush-border membranes and the peroxidase activity was determined in a spectrophotometer. The number of soybean agglutinin binding sites in the brush-border membranes has been established by means of iterized computer fit analysis of the data, indicating values for maximal binding of 7.10(-7) M soybean agglutinin per mg of brush-border membrane protein and a dissociation constant of 1.5.10(-5) M.

Animals↗
PubMed1983

Lectin receptors on the plasma membrane of soybean cells. Binding and lateral diffusion of lectins.

Protoplasts prepared from suspension cultures of root cells of Glycine max (SB-1 cell line) bound soybean agglutinin (SBA), concanavalin A (Con A), and wheat germ agglutinin (WGA). Binding studies carried out with 125I-labeled SBA, Con A, and WGA showed that these interactions were saturable and specific. Fluorescence microscopy demonstrated uniform membrane labeling. The mobility of the lectin-receptor complexes was measured by fluorescence redistribution after photobleaching. The diffusion constants (D) for SBA and Con A were 5 X 10(-11) and 7 X 10(-11) cm2/s, respectively. In contrast, WGA yielded a diffusion constant of 3 X 10(-10) cm2/s. Pretreatment of the protoplasts with either SBA or Con A resulted in a 6-fold reduction in the mobility of WGA (D congruent to 5 X 10(-11) cm2/s). The results suggest that the binding of SBA or Con A may lead to alterations of the soybean plasma membrane which, in turn, may restrict the mobility of other receptors.

Cell Membrane↗