Expression of cDNA for a bark lectin of Robinia in transgenic tobacco plants

Quantitative evaluation of glycan-binding specificity of recombinant concanavalin A produced in lettuce (Lactuca sativa)

Concanavalin A (ConA), a mannose (Man)-specific leguminous lectin isolated from the jack bean (Canavalia ensiformis) seed extracts, was discovered over a century ago. Although ConA has been extensively applied in various life science research, recombinant mature ConA expression has not been fully established. Here, we aimed to produce recombinant ConA (rConA) in lettuce (Lactuca sativa) using an Agrobacterium tumefaciens-mediated transient expression system. rConA could be produced as a fully active form from soluble fractions of lettuce leaves and purified by affinity chromatography. From 12 g wet weight of lettuce leaves, 0.9 mg rConA could be purified. The glycan-binding properties of rConA were then compared with that of the native ConA isolated from jack bean using glycoconjugate microarray and frontal affinity chromatography. rConA demonstrated a glycan-binding specificity similar to nConA. Both molecules bound to N-glycans containing a terminal Man residue. Consistent with previous reports, terminal Manα1-6Man was found to be an essential unit for the high-affinity binding of rConA and nConA, while bisecting GlcNAc diminished the binding of rConA and nConA to Manα1-6Man-terminated N-glycans. These results demonstrate that the fully active rConA could be produced using the A. tumefaciens-mediated transient expression system and used as a recombinant substitute for nConA.

Expression of Lectins in Heterologous Systems

Lectins are proteins that have the ability to recognize and bind in a reversible and specific way to free carbohydrates or glycoconjugates of cell membranes. For these reasons, they have been extensively used in a wide range of industrial and pharmacological applications. Currently, there is great interest in their production on a large scale. Unfortunately, conventional techniques do not provide the appropriate platform for this purpose and therefore, the heterologous production of lectins in different organisms has become the preferred method in many cases. Such systems have the advantage of providing better yields as well as more homogeneous and better-defined properties for the resultant products. However, an inappropriate choice of the expression system can cause important structural alterations that have repercussions on their biological activity since the specificity may lay in their post-translational processing, which depends largely on the producing organism. The present review aims to examine the most representative studies in the area, exposing the four most frequently used systems (bacteria, yeasts, plants and animal cells), with the intention of providing the necessary information to determine the strategy to follow in each case as well as their respective advantages and disadvantages.

Production of recombinant single chain antibodies (scFv) in vegetatively reproductive Kalanchoe pinnata by in planta transformation

We developed an asexual reproductive plant, Kalanchoe pinnata, as a new bioreactor for plant-based molecular farming using a newly developed transformation method. Leaf crenate margins were pin-pricked to infect the plant with the Agrobacterium strain LBA4404 and vacuum infiltration was also applied to introduce the target gene into the plants. Subsequently, the young mother leaf produced new clones at the leaf crenate margins without the need for time- and labor-consuming tissue culture procedures. The average transformation rates were approximately 77 and 84% for pin-prickling and vacuum-infiltration methods, respectively. To functionally characterize an introduced target protein, a nucleic acid hydrolyzing recombinant 3D8 scFv was selected and the plant based 3D8 scFv proteins were purified and analyzed. Based on abzyme analysis, the purified protein expressed with this system had catalytic activity and exhibited all of properties of the protein produced in an E. coli system. This result suggested that vegetatively reproductive K. pinnata can be a novel and potent bioreactor for bio-pharmaceutical proteins.

Modulation of a lectin insecticidal activity by carbohydrates

Lectins from plants present an insecticidal activity most probably through their carbohydrate binding properties; as a consequence, their toxicity should vary with the presence of a competitive sugar in the ingested food. In order to test this hypothesis, we performed competition experiments between insecticidal activity and carbohydrate binding. For this purpose, we used a lectin from Lathyrus ochrus and the specific carbohydrate for this protein, glucose. In toxicological tests with Drosophila melanogaster, we observed a decrease of lectin toxicity when glucose was added to the larva-rearing medium. This result suggests that the toxicity of the lectin is correlated to its ability to bind sugar in the insect digestive tract and stresses the importance of sugar composition of the nutriment used for toxicological testing of lectins or in genetically modified plants.

Modification of plant components

With respect to plant biotechnology, 1995 and 1996 will be marked by the commercialization of the first genetically engineered plant oil and a number of ground-breaking publications. The modification of plant components using transgenic technology is not just 'switching' phenotypes from one host to another, rather, it is a means for producing valuable novel products that are normally not found (or are difficult to find) in plants. Active research is being carried out with similar schemes in both academic laboratories and biotechnology companies. As a result, the traditional line that separates the 'basic' research of universities and the 'practical' work of industry is becoming fuzzy. Although many roadblocks remain, judging from the progress made in the past two years, the genetic engineering of plant components is heading towards a bright and exciting future.

Radiolabeling of lectin from Robinia pseudoacacia by reductive methylation

Lectin from the bark of Robinia pseudoacacia was radiolabeled by reductive methylation. Reductive methylation of the lectin with [14C]formaldehyde and a reducing agent, sodium borohydride, resulted in incorporation of 14C into the lectin but with considerable inactivation of carbohydrate binding activity. Dialysis of the labeled lectin against the buffer containing Ca2+ and Mn2+ partially restored the activity. Higher incorporation of 14C into the lectin was observed when sodium cyanoborohydride was used as a reducing agent. In this case, more than eighty percent of the labeled lectin retained carbohydrate binding activity. Autoradiography showed that the radiolabeled lectin had a molecular mass of 29 kDa, corresponding to that of the intact lectin subunit.