Plant lectins, chemical and biological aspects

Abstract

Lectins, carbohydrate-binding proteins of non-immune origin, that agglutinate cells or precipitate polysaccharides and glycoconjugates, are well distributed in nature, mainly in the Plant Kingdom. The great majority of the plant lectins are present in seed cotyledons where they are found in the cytoplasm or in the protein bodies, although they have also been found in roots, stems and leaves. Due to their peculiar properties, the lectins are used as a tool both for analytical and preparative purposes in biochemistry, cellular biology, immunology and related areas. In agriculture and medicine the use of lectins greatly improved in the last few years. The lectins, with few exceptions, are glycoproteins, need divalent cations to display full activity and are, in general, oligomers with variable molecular weight. Although the studies on lectins have completed a century, their role in nature is yet unknown. Several hypotheses on their physiological functions have been suggested. Thus, lectins could play important roles in defense against pathogens, plant-microorganism symbiosis, cell organization, embryo morphogenesis, phagocytosis, cell wall elongation, pollen recognition and as reserve proteins. A brief review on the general properties and roles of the lectins is given.

The carbohydrate-binding specificity and molecular modelling of Canavalia maritima and Dioclea grandiflora lectins

“…In recent years, lectins have become very attractive proteins due to their extensive use as probes for both the characterization and isolation of simple and complex sugars and as useful tools in immunological studies (Moreira et al 1991). Accordingly, lectins are, by now, the plant proteins of best known three-dimensional structures.…”

Antimicrobial activity of lectins from Antimicrobial Activity of Lectins from Plants

“…Most lectins are present in seed cotyledons of the plant (but also found in any other parts such as roots, stems, rhizomes, and leaves in lesser amounts). In such tissues, most lectins are located within cytoplasm or protein bodies inside the cells (Moreira et al, 1991). In general, the lectins with the same ligand specificity contain different binding abilities mainly depended on their sources meant different genetic material that produce different lectins with different in three dimension structures.…”

“…One familiar instance which the lectin usage is clearly seen is ABO blood type identification using blood group specific lectin such as Concanavalin A, a lectin derived from jack bean seed (Canavalia ensiformis) that can specifically bind to non-reducin α-terminal mannose. This blood groups determination is based on presence or absence of specific glycoprotein on red blood cells that the lectins can bind and make red blood cells agglutination (Moreira et al, 1991) by forming network with red blood cells and then can not be collected as button like form in the U shape bottom well. From this incident, a method widely used for lectin screenings or characterizations mainly involved cells agglutination, especially red blood cells from various animals (Sharon and Lis, 2001).…”

“…The lectins also have other roles in mammals. There was evidences indicated that the lectins played the important roles in cell differentiation, cell movement and phagocytosis, cell to cell and cells to matrix substances communication, cell organization in tissues, and embryo morphogenesis (Moreira et al, 1991).…”

“…It is believed that production and accumulation of toxic lectins in some plants are a kind of defending mechanisms which plants develop for protecting them form certain plant eating organisms such as insects and mammals and plant pathogens. Aside from defense mechanisms, the lectins also have their essential roles in plant-microorganism symbiosis, cell differentiation, pollen recognition, cell wall elongation, and as a reserved protein (Moreira et al, 1991). Interestingly, some plant lectins were found to be well react with viral surface glycoprotein and were hoped to use in controlling many diseases originated from viruses which current methods are still inadequate controllable efficiencies.…”