Investigation on the occurrence of soluble lectins in mammalian nervous tissue extracts

Histochemical localization of a beta-galactoside-binding lectin and its binding-sites in developing and adult rat cochlea

The presence of an endogenous rat beta-galactoside-specific lectin (S-Lac) and its specific binding ligands was analyzed, using a rabbit anti-human brain lectin of 14 kDa antibody (anti-HBL-14) and a probe consisting of a biotinylated derivative of the human lectin (HBL-biot) in adult and in developing rat cochleas. At PD1, some epithelial cells of the outer spiral sulcus (OSS) were specifically recognized by the anti-HBL-14 antibody. Then, anti-HBL-14 immunoreactivity progressively appeared in all OSS epithelial cells, and, from PD9 on, it also appeared in inner spiral sulcus (ISS) epithelial cells. Finally, young adult rats exhibited a well defined anti-HBL-14 immunoreactivity in epithelial cells of the inner and outer spiral sulcus. Using the biotinylated probe, from PD3 on, tectorial membrane (TM) and the sensory cells apical surfaces were labelled. The glycoconjugate expression within the developing organ of Corti seems to be highly complex. Lectin was detected in developing and adult epithelial cells surrounding the organ of Corti. In contrast, other glycoconjugates related to B and H human blood group antigens, were transiently present on sensory cells of the organ of Corti. Present findings can be correlated with significant events in development of the cochlea, mainly with cell-cell recognition or cellular adhesion.

Biotinylated derivative of a human brain lectin: synthesis and use in affinoblotting for endogenous ligand studies

Coupling of biotin to an endogenous lectin yields a probe which can be used for selective nonradioactive detection of complementary endogenous ligands. To exemplify practical applications of this type of compounds, we have synthesized and characterized a biotinylated derivative of a beta-galactoside-specific human brain lectin. Proteins which bind this lectin can be located on nitrocellulose sheets after electrophoretic transfer from gradient polyacrylamide gels, by sequential incubation with biotinylated probes and streptavidin-peroxidase, with visualization by an insoluble reaction product (affinoblotting). Biotinylated galactoside-binding plant lectins were used in the same way to visualize human brain glycoproteins, and their binding specificity was compared with that of human brain lectin. The results obtained by means of these different probes showed the usefulness of the endogenous lectin derivative to actually identify its endogenous partners. Thus this approach may find extended applications in the study of biological activities of vertebrate lectins in homologous systems, i.e., with lectins and ligands coming from the same tissue origin.

Mapping of receptors for carbohydrate constituents of glycoconjugates in well-differentiated and malignant ependymomas: a glycohistochemical study

Recognitive interactions between the carbohydrate part of cellular glycoconjugates and endogenous receptors supposedly govern important biological processes. Consequently, their elucidation can be of considerable value in tumour diagnosis. The histochemical patterns of expression of endogenous sugar receptors (e.g. endogenous lectin-like proteins) of 10 cases of well-differentiated ependymoma and 10 cases of malignant ependymoma were analysed, using a panel of 18 biotinylated (neo)glycoproteins and a standardized staining protocol. Within this panel, differences in the extent of staining for intracellular sugar receptors in well-differentiated and malignant ependymomas were histochemically detectable. In comparison to the well-differentiated ependymomas, the anaplastic form of the tumour exhibited a generally higher capacity to specifically bind labelled (neo)glycoproteins, containing alpha- or beta-glucosides and a disaccharide, characteristic for one type of beta-galactoside-terminated chain structure of glycoproteins. A significantly reduced binding was seen for tumours of the anaplastic type with labelled markers, carrying histochemically indispensable glucuronic acid residues. These findings suggest that labelled neoglycoproteins are a valuable tool for assessing the endogenous sugar-binding capacity in diagnostic histopathology. Our descriptive analysis of endogenous sugar receptors may also be a rational basis for studies on the functional significance of changes in the expression of their endogenous ligands and the cellular glycoconjugates. Further investigations are also possible on the correlation between the degree of differentiation and expression of both parts of a recognitive system, based on protein (receptor)-carbohydrate (ligand) interactions, in tumours of the central nervous system, especially ependymomas.

Purification and characterization of a galactoside-binding lectin from human brain

A beta-galactoside-binding hemagglutinin was detected in soluble extracts of human brain. This soluble lectin was purified to homogeneity by affinity column chromatography on lactose coupled to divinylsulfone-activated agarose. The purified lectin had an isoelectric point of 3.9 and its subunit molecular mass estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate was 14,500. Human brain lectin was not a glycoprotein and its amino acid composition was characterized by a high content of serine, glutamic acid, and glycine, and a low content of methionine and cysteine. The most potent saccharide inhibitors tested were thiodigalactoside, lactose, and p-nitrophenyl-beta-D-galactoside. An antibody was raised to the pure lectin. Immunological relationships were found between the brain lectin and several other soluble lectins of various vertebrate origins.