Lectins and their uses as biotechnological tools

Application of lectin immobilized on polyHIPE monoliths for bioprocess monitoring of glycosylated proteins

In-process monitoring of glycosylated protein concentration becomes very important with the introduction of perfusion bioprocesses. Affinity chromatography based on lectins allows selective monitoring when carbohydrates are accessible on the protein surface. In this work, we immobilized lectin on polyHIPE type of monoliths and implemented it for bioprocess monitoring. A spacer was introduced to lectin, which increased binding kinetics toward Fc-fusion protein, demonstrated by bio-layer interferometry. Furthermore, complete desorption using 0.25 M galactose was shown. Affinity column exhibited linearity in the range between 0.5 and 8 mg/ml and flow-unaffected binding for the flow-rates between 0.5 and 8 ml/min. Long-term stability over at least four months period was demonstrated. No unspecific binding of culture media components, including host cell proteins and DNA, was detected. Results obtained by affinity column matched concentration values obtained by a reference method.

ACL-I, a lectin from the marine sponge Axinella corrugata: isolation, characterization and chemotactic activity

The lectin from the marine sponge Axinella corrugata (ACL-I) was purified by affinity chromatography on rabbit erythrocytic stroma incorporated into a polyacrylamide gel followed by gel filtration on Ultrogel AcA 44 column. Purified ACL-I is a hexameric glycoprotein with a Mr of 82.3 kDa estimated by SDS-PAGE and 78.5 kDa by FPLC on Superose 12 HR column. The pI of lectin is 6.3 and ACL-I is constituted of 13.9 kDa similar subunits some of them linked by disulphide bridges. This lectin agglutinates native rabbit, goat and dog erythrocytes and in less extent human erythrocytes. The hemagglutinating activity is independent of Ca(2+), Mg(2+) and Mn(2+), but it is strongly inhibited by carbohydrates containing N-acetyl groups. ACL-I is stable up to 70 degrees C for 30 min, with optimum pH between 7 and 8, and it is also resistant to enzymatic proteolysis in vitro. In the presence of reducing or denaturant agents, the lectin activity decreases. ACL-I displays chemotactic effect on rat neutrophil in vitro which is inhibited by N-acetyl-d-glucosamine.

Self-aggregation of legume seed storage proteins inside the protein storage vacuoles is electrostatic in nature, rather than lectin-mediated

Conglutins are multisubunit, glycosylated, major storage proteins present in Lupinus seeds that self-aggregate in a calcium/magnesium-dependent manner. Two of these globulins exhibit lectin activity. The 210 kDa globulin derived from beta-conglutin that accumulates in Lupinus cotyledons during germination was used as a model protein to establish whether the self-aggregation process is electrostatic in nature or lectin-mediated. This protein binds in a very strong manner to chitin and recognizes a variety of glycoproteins including immunoglobulins G. Several compounds were tested for their inhibitory effect on the cation-dependent self-aggregation process. Sialic acid and phytin were the most effective whereas chitin and mucin were totally ineffective. The inability of the oligosaccharidic side chains of the 210 kDa protein, beta-conglutin and immunoglobulin G to interfere with the aggregation strongly supports the view that Ca/Mg are electrostatically involved in the in vitro self-aggregation of Lupinus globulins. The results suggest that calcium and magnesium ions are also electrostatically involved in vivo in the macromolecular aggregation of legume seed storage proteins, ensuring their efficient packing inside the protein storage vacuoles. This mechanism is responsible for the typical insolubility of legume globulins in water.

Glycohistochemistry: the why and how of detection and localization of endogenous lectins

The central dogma of molecular biology limits the downstream flow of genetic information to proteins. Progress from the last two decades of research on cellular glycoconjugates justifies adding the enzymatic production of glycan antennae with information-bearing determinants to this famous and basic pathway. An impressive variety of regulatory processes including cell growth and apoptosis, folding and routing of glycoproteins and cell adhesion/migration have been unravelled and found to be mediated or modulated by specific protein (lectin)-carbohydrate interactions. The conclusion has emerged that it would have meant missing manifold opportunities not to recruit the sugar code to cellular information transfer. Currently, the potential for medical applications in anti-adhesion therapy or drug targeting is one of the major driving forces fuelling progress in glycosciences. In histochemistry, this concept has prompted the introduction of carrier-immobilized carbohydrate ligands (neoglycoconjugates) to visualize the cells' capacity to be engaged in oligosaccharide recognition. After their isolation these tissue lectins will be tested for ligand analysis. Since fine specificities of different lectins can differ despite identical monosaccharide binding, the tissue lectins will eventually replace plant agglutinins to move from glycan profiling and localization to functional considerations. Namely, these two marker types, i.e. neoglycoconjugates and tissue lectins, track down accessible binding sites with relevance for involvement in interactions in situ. The documented interplay of synthetic organic chemistry and biochemistry with cyto- and histochemistry nourishes the optimism that the application of this set of innovative custom-prepared tools will provide important insights into the ways in which glycans can act as hardware in transmitting information during normal tissue development and pathological situations.

Effects of tacrine upon murine neuroblastoma cells

Tacrine [9-amino-1,2,3,4-tetrahydroacridine] (THA), a potent acetylcholinesterasic inhibitor, is utilized in the pharmacological treatment of Alzheimer's disease (Birne and Arie, 1994). Cytopharmacology of THA is still largely to be discovered. In the present paper we report some effects produced by THA on murine neuroblastoma cells (N2A) used as an experimental model. N2A cells treated with THA at low concentration (1 mu M) showed a reduced cell's mitosis and a remarkable reduction of protein synthesis. Eventually, a marked reduction on the phosphorylation of proteins associated to neurofilaments 200 kD, is observed using specific antibody.