The isolectins of Helix pomatia. Separation by isoelectric focusing and preliminary characterization

H-type lectins - Structural characteristics and their applications in diagnostics, analytics and drug delivery

Lectins are ubiquitous carbohydrate-binding proteins that interact with sugar moieties in a highly specific manner. H-type lectins represent a new group of lectins that were identified in invertebrates. These lectins share structural homology and bind mainly to N-acetylgalactosamine (GalNAc). Recent structural studies on the H-type lectins provided a detailed description of the GalNAc-lectin interaction that is already exploited in a number of biomedical applications. Two members of the H-type lectin family, Helix pomatia agglutinin (HPA) and Helix aspersa agglutinin (HAA), have already been extensively used in many diagnostic tests due their ability to specifically recognize GalNAc. This ability is especially important because aberrant glycosylation patterns of proteins expressed by cancer cells contain GalNAc. In addition, H-type lectins were utilized in diagnostics of other non-cancer diseases and represent great potential as components of drug delivery systems. Here, we present an overview of the H-type lectins and their applications in diagnostics, analytics and drug delivery.

Identification, cloning, and characterization of two N-acetylgalactosamine-binding lectins from the albumen gland of Helix pomatia

Helix pomatia agglutinin (HPA), the lectin from the albumen gland of the Roman snail, has been used in histochemical studies relating glycosylation changes to the metastatic potential of solid tumors. To facilitate the use of HPA in a clinical (diagnostic) setting, detailed analysis of the lectin, including cloning and recombinant production of HPA, is required. A combination of isoelectric focusing, amino acid sequence analysis, and cloning revealed two polypeptides in native HPA preparations (HPAI and HPAII), both consistent with GalNAc-binding lectins of the H-type family. Pairwise sequence alignment showed that HPAI and HPAII share 54% sequence identity whereas molecular modeling using SWISS-MODEL suggests they are likely to adopt similar tertiary structure. The inherent heterogeneity of native HPA highlighted the need for production of functional recombinant protein; this was addressed by preparing His-thioredoxin-tagged fusion products in Escherichia coli Rosetta-gami B (DE3) cells. The recombinant lectins agglutinated human blood group A erythrocytes whereas their oligosaccharide specificity, evaluated using glycan microarrays, showed that they predominantly bind glycans with terminal α-GalNAc residues. Surface plasmon resonance with immobilized GalNAc-BSA confirmed that recombinant HPAI and HPAII bind strongly with this ligand (K(d) = 0.60 nm and 2.00 nm, respectively) with a somewhat higher affinity to native HPA (K(d) = 7.67 nm). Recombinant HPAII also bound the breast cancer cells of breast cancer tissue specimens in a manner similar to native lectin. The recombinant HPA described here shows important potential for future studies of cancer cell glycosylation and as a reagent for cancer prognostication.

Biochemical and Structural Analysis of Helix pomatia Agglutinin

Helix pomatia agglutinin (HPA) is a N-acetylgalactosamine (GalNAc) binding lectin found in the albumen gland of the roman snail. As a constituent of perivitelline fluid, HPA protects fertilized eggs from bacteria and is part of the innate immunity system of the snail. The peptide sequence deduced from gene cloning demonstrates that HPA belongs to a family of carbohydrate-binding proteins recently identified in several invertebrates. This domain is also present in discoidin from the slime mold Dictyostelium discoideum. Investigation of the lectin specificity was performed with the use of glycan arrays, demonstrating that several GalNAc-containing oligosaccharides are bound and rationalizing the use of this lectin as a cancer marker. Titration microcalorimetry performed on the interaction between HPA and GalNAc indicates an affinity in the 10(-4) M range with an enthalpy-driven binding mechanism. The crystal structure of HPA demonstrates the occurrence of a new beta-sandwich lectin fold. The hexameric quaternary state was never observed previously for a lectin. The high resolution structure complex of HPA with GalNAc characterizes a new carbohydrate binding site and rationalizes the observed preference for alphaGalNAc-containing oligosaccharides.

N-acetyl-d-galactosamine/N-acetyl-d-glucosamine – recognizing lectin from the snailCepaea hortensis: purification, chemical characterization, cloning and expression inE. coli

From the albumin gland of the snail Cepaea hortensis we isolated and characterized a new N-acetyl-D-galactosamine/N-acetyl-D-glucosamine (GalNAc/GlcNAc) specific lectin (CHA-II) which was purified by a combination of affinity chromatography on GalNAc-agarose and gel filtration. The purified native lectin was found to be a multimeric protein, as revealed by SDS-PAGE and MALDI-TOF analysis. In SDS-PAGE the denatured and reduced lectin showed two bands of molecular masses with 17 and 15.5 kDa which reacted equally with anti-CHA-II rabbit antiserum. The lectin was O- and N-glycosylated with [(Gal)2-Man]2-Man-GlcNAc-GlcNAc-Asn as a probable structure for the oligosaccharide. Isoelectric focusing revealed a heterogeneous protein of at least four bands around pH 8.7. Tryptic peptides of CHA-II were N-terminally sequenced and highly degenerated gene specific oligonucleotide primers (GSPs) had been constructed. Using total RNA isolated from albumin glands, cDNAs were produced by the running race technique. Specific PCR fragments were obtained by PCR using GSPs, the universal primer and 5'- or 3'-RACE-cDNAs. The amplified fragments were cloned into the vector pDrive and were sequenced. The resulting total cDNA sequence consisted of 496 base pairs including an open reading frame of 360 base pairs which encoded a protein of 120 amino acids. The protein carried a putative signal peptide. The mature protein was predicted to comprise 99 amino acid residues with a calculated molecular weight of 11,239 Da. The PCR fragment encoding the mature protein was cloned into the vector pQE30 and expressed in E. coli. Recombinant CHA-II lectin was produced as inclusion bodies and extracted by 6 M guanidine hydrochloride. After refolding, the recombinant CHA-II agglutinated specifically human red blood cells of groups A and AB. In immunodiffusion experiments using rabbit antiserum raised against the native lectin, the protein showed a precipitation line of identity with the native lectin.

Morphological aspects of Achacin-treated bacteria

1. The morphology of bacteria treated with the bactericidal glycoprotein, Achacin, purified from the giant African snail, Achatina fulica Férussac, has been studied. 2. Achacin lengthens the bodies of Escherichia coli by three to seven times. 3. Achacin damages the surface of Staphylococcus aureus and sinks the cytoplasmic membranes into the cytoplasm. 4. Achacin causes neither the leakage nor the destruction of cells.

Molecular cloning of the antibacterial protein of the giant African snail, Achatina fulica Férussac

An expression cDNA library was constructed with poly(A)-rich RNA extracted from the collar of the giant African snail, Achatina fulica Férussac. A 1.9-kbp cDNA clone encoding a precursor of antibacterial glycoprotein of the snail, achacin, was isolated from the cDNA expression library. The cDNA sequence contains an open reading frame with 1593-nucleotide residues. The deduced amino acid sequence of this achacin precursor starts with a 29-residue leader peptide followed by a 502-residue mature peptide (56 kDa) with four possible N-glycosylation sites, Asn-Xaa-Ser or Asn-Xaa-Thr. The Northern-blot analysis proved that the achacin precursor was specifically expressed in the tissue of snail collar and processed to mature achacin. cDNA inserts encoding achacin precursor were subcloned into expression plasmids. Three kinds of expressed polypeptides were cross-reacted with rabbit antiserum raised against achacin. The largest polypeptide (M(r) 63,000) should be the achacin precursor.

Bactericidal action of a glycoprotein from the body surface mucus of giant African snail

1. Bactericidal action of a glycoprotein, Achacin, purified from the giant African snail, Achatina fulica Férussac, has been studied. 2. Achacin kills both gram-positive and gram-negative bacteria, but only in their growing states. 3. Achacin does not have any bacteriolytic activity. 4. The strain which has no cell wall is a little more sensitive than the native strain and the cell membrane-damaged strain. 5. Achacin was observed on the cytoplasmic membrane and on the cell wall of treated Escherichia coli by immunoelectron microscopy. 6. Achacin attacks the cytoplasmic membrane of the cell.

Rapid detection of herpes simplex virus with fluorescein-labeled Helix pomatia lectin

The use of fluorescein-conjugated Helix pomatia lectin was shown to be as effective as fluorescein-conjugated monoclonal antibody reagents for the detection and differentiation of herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2) in MRC-5 cell culture. Cells infected with HSV-1 generally displayed a pattern of nongranular or diffuse fluorescence, while cells infected with HSV-2 were identified by the production of fluorescent grains and flecks. This unique nonimmunological reagent, when used in combination with low-speed centrifugation, provides a remarkably specific, sensitive, rapid, and cost-effective means to detect HSV-infected MRC-5 or BHK-21 cells as early as 20 h postinoculation. In contrast to the immunofluorescence method, the serotypes of HSV can be differentiated with only one fluorescein-H. pomatia reagent in MRC-5 cell cultures.

Comparative analysis of agglutinins from hemolymph and albumin gland of Helix pomatia

The hemolymph of Helix pomatia contains a weak agglutinating activity. This lectin concentration was calculated to be about 1.8 micrograms.ml-1. Among the different red blood cells tested, pronase-treated sheep erythrocytes were found to be the most suitable indicator cells. Their agglutination could be inhibited by GalNAc and GlcNAc. The serum agglutinin was isolated by affinity chromatography using Sephadex G-200 as the matrix. It exhibited a single band in discontinuous PAGE. In the presence of SDS, subunits of 27,000 daltons were obtained which, after addition of 2-mercaptoethanol, partly dissociated into 13,000-dalton subunits. The biochemical properties observed were compared with those of the well-known blood group A-specific lectin from the albumin gland of H. pomatia.

Analysis of differentiation and transformation of cells by lectins

During differentiation cells are known to change their biological behavior according to their genotype. This is thought to be accompanied by a modulation of cell surface determinants expressed on the outer cell membrane. Vice versa, cell surface molecules are suggested to mediate extracellular signals to the genome. Most of these molecules integrated in the cell membrane have been proven to be glycoconjugates. The carbohydrate moieties of these molecules can be detected by means of lectins that are characterized by their ability to react specifically with distinct terminal sugar sequences. Thus, lectins have been used as appropriate tools for studying the modulation of functionally important membrane-associated molecules during the differentiation of cells, in particular of B- and T-lymphocytes. Moreover, lectins have been proven to distinguish between differentiated cells and malignant cell clones, according to the hypothesis that transformed cells possess a glycoconjugate profile that corresponds to the stage of differentiation at which they are arrested. Since lectins, like monoclonal antibodies, make it possible to study functionally important molecules that are associated with differentiation and malignancy, they might be of value for diagnostic purposes and, moreover, for analyzing malignant transformation.

A new agglutinin from the Tulipa gesneriana bulbs

Two agglutinins with different agglutinating activity exist in Tulipa gesneriana bulbs. One is the T. gesneriana lectin which agglutinates yeasts as reported previously [Oda, Y. and Minami, K. (1986) Eur. J. Biochem. 159, 239-245]. The other agglutinin is a new one which agglutinates animal erythrocytes and was purified from the tulip bulbs using affinity chromatography on thyroglobulin-Sepharose 4B. The agglutinin agglutinated mouse and rat erythrocytes at a minimum concentration of 2 micrograms/ml and 30 micrograms/ml respectively, but did not agglutinate erythrocytes from other animals and yeasts even at a concentration of 1000 micrograms/ml. The agglutinin appeared homogeneous by disc gel electrophoresis at pH 4.3 and gel filtration. Its relative molecular mass was determined by gel filtration to be approximately 40,000. It was suggested that the agglutinin was composed of two different subunits of 26 kDa and 14 kDa by sodium dodecyl sulfate/polyacrylamide gel electrophoresis analysis. Binding of radioiodinated agglutinin to mouse erythrocytes indicated that the presence of a high-affinity site with a dissociation constant of 2.00 X 10(-9) M. In inhibition experiments thyroglobulin glycopeptides were the most potent inhibitors; thyroglobulin was also a potent inhibitor. Orosomucoid and mucin showed weak inhibition. The other glycoproteins, glycopeptides and sugars examined showed no inhibition.

Protein blotting: detection of proteins with colloidal gold, and of glycoproteins and lectins with biotin-conjugated and enzyme probes

Methods to detect "native" proteins immobilized on nitrocellulose membranes in spot tests or on blots prepared from polyacrylamide slab gels after electrophoretic separation are described. Gold sols were found to be useful as general stains for proteins: They are polychromatic, yield an indelible record, and are complementary to india ink as protein stains because these two stains have different sensitivities for a number of proteins tested. For detection of wheat germ lectin (WGL)-binding glycoproteins, avidin-peroxidase was an effective enzyme probe, because the glycoportion of the avidin moiety possesses binding affinity to WGL. Glycocomponents in human parotid saliva were detected with this probe and with the following biotin-conjugated lectins as intermediary probes: soybean lectin, Bandeiraea simplicifolia lectin, Lotus tetragonolobus lectin, and kidney bean lectin. Autoclaving blots prior to probing eliminated endogenous peroxidase activity. Concanavalin A and WGL were separated by isoelectric focusing and detected on blots with horseradish peroxidase and avidin-peroxidase, respectively. The versatility of the biotin/avidin system was used to detect other lectins on similar blots using biotin-conjugated glycoproteins as intermediary probes: Helix pomatia lectin and B. simplicifolia lectin were detected with biotinyl neoglycoproteins, and kidney bean lectin with biotin-conjugated components of parotid saliva.

A structural comparison of the A and B subunits of Griffonia simplicifolia I isolectins

A structural comparison between the A and B subunits of the five tetrameric Griffonia simplicifolia I isolectins (A4, A3B, A2B2, AB3, B4) was undertaken to determine the extent of homology between the subunits. The first 25 N-terminal amino acids of both A and B subunits were determined following the enzymatic removal of N-terminal pyroglutamate blocking groups with pyroglutamate aminopeptidase. Although 21 amino acids were common to both subunits, there were four unique amino acids in the N-terminal sequence of A and B. Residues 8, 9, 17, and 19 were asparagine, leucine, lysine, and asparagine in subunit A and threonine, phenylalanine, glutamic acid, and serine in subunit B. The last six C-terminal amino acids, released by digestion with carboxypeptidase Y, were the same for both subunits: Arg-(Phe, Val)-Leu-Thr-Ser-COOH. Subunit B, which contains one methionyl residue, was cleaved by cyanogen bromide into two fragments, a large (Mr = 31,000) and a small (Mr = 2700) polypeptide. Failure of the small fragment to undergo manual Edman degradation indicated an N-terminal blocking group, presumably pyroglutamate. Both subunits were digested with trypsin and the tryptic peptides were analyzed using reverse-phase HPLC. Tryptic glycopeptides were identified by labeling the carbohydrate moiety of the A and B subunit using sodium [3H] borohydride. Cysteine-containing tryptic peptides were similarly identified by using [1-14C]iodoacetamide. Approximately 30% of the tryptic peptides were common to both subunits. Thus, although the N- and C-terminal regions of A and B are similar, the subunits each possess unique sequences.