Screening for and purification of novel self-aggregatable lectins reveal a new functional lectin group in the bark of leguminous trees

Autoactivation of pancreatic trypsinogen is controlled by carbohydrate-specific interaction

Activation of bovine pancreatic trypsinogen (BPTG) by trypsin (BPT) was found to be inhibited by d GalN/GalNAc at pH 5.5, the pH of secretory granules in the pancreas. Binding studies with biotinylated sugar-polymers indicated that BPTG and BPT bind to α-GalNAc, α-Man, and α-Gal better at pH 5.5 than at pH 7.5. Ultraviolet-difference spectra indicated that BPTG binding to α-GalNAc differs substantially from BPTG binding to other sugars. The N-α-benzoyl-d,l-arginine-p-nitroanilide hydrochloride-hydrolyzing activity of BPT was only slightly affected by these sugars. The results indicate that the binding of GalNAc - containing glycoconjugates protects BPTG from autoactivation, and this may be a self-defense mechanism against intrapancreatic activation.

Preparation of affinity adsorbents and purification of lectins from natural sources

Lectins are purified by affinity chromatography to take advantage of their carbohydrate-specific interactions. Highly efficient affinity adsorbents are powerful tools to obtain homogeneous lectins with distinct specificities. Here, we describe three methods to prepare affinity adsorbents by immobilizing carbohydrates or glycoconjugates on agarose gel beads. Because the ligands are immobilized via a stable and nonionic linkage under mild conditions, the adsorbents possess high binding capacity for lectins with low nonspecific adsorption and can withstand repeated use. The procedures require neither specialized techniques and apparatus nor highly toxic compounds. Using these adsorbents, many plant and animal lectins can be purified in a few steps.

A novel family of lectins evolutionarily related to class V chitinases: an example of neofunctionalization in legumes

A lectin has been identified in black locust (Robinia pseudoacacia) bark that shares approximately 50% sequence identity with plant class V chitinases but is essentially devoid of chitinase activity. Specificity studies indicated that the black locust chitinase-related agglutinin (RobpsCRA) preferentially binds to high-mannose N-glycans comprising the proximal pentasaccharide core structure. Closely related orthologs of RobpsCRA could be identified in the legumes Glycine max, Medicago truncatula, and Lotus japonicus but in no other plant species, suggesting that this novel lectin family most probably evolved in an ancient legume species or possibly an earlier ancestor. This identification of RobpsCRA not only illustrates neofunctionalization in plants, but also provides firm evidence that plants are capable of developing a sugar-binding domain from an existing structural scaffold with a different activity and accordingly sheds new light on the molecular evolution of plant lectins.