What Are Lectins?

Lectin refers to a glycoprotein or a glycoprotein that is purified from various plants, invertebrates, and higher animals. Because it can agglutinate red blood cells (containing blood group substances), it is called lectin. Phytoagglutin (PNA) is commonly used, and it is usually named after the plant it is extracted from, such as Concanvalina (ConA), Wheat germ agglutinin (WGA), and Peanut agglutinin (Peanut agglutinin, PNA) and Soybean agglutinin (SBA), etc., lectin is their collective name.

Lectin is

Lectin application

It is generally believed that specific glycosyl groups on the cell membrane can be used to distinguish cell types and reflect changes in cell differentiation, maturity, and tumor cell changes. Only in some special cases, the properties of cell-binding lectins can be estimated in advance, such as the specificity of crocetin to blood group A substance, and the statin of virgin lectin to blood group O substance 2-L-fucose Specificity, however, in most cases, the types of carbohydrate determinants recognized by lectins, and the properties and functions of the molecules that carry the determinants are completely discovered through experimental experience.

Lectin classification

Lectins can be classified by their specificity, molecular structure, binding site, and function. Animal lectins are classified into C-type lectin, S-type lectin, P-type lectin, I-type lectin, and pentraxins according to their molecular structure. C-type lectin is a Ca2 + -dependent lectin; S-type lectin is a lectin that specifically recognizes -galactosyl bonds; P-type lectin is a lectin that specifically recognizes mannose 6 phosphate; I- Type lectins are lectins similar to immunoglobulins; pentraxins are lectins with five subunits.

Lectin properties

Lectins found in invertebrates so far are glycoproteins, and sugars are incorporated into lectins in the form of covalent bonds. The types of sugars mainly include mannose, glucosamine, and galactose, and xylose and arabinose are rare. The types of sugars contained in animal lectins are different from the types of sugars contained in plants and microbial lectins. The protein part of lectins is mainly composed of aspartic acid, serine, and threonine, and rare sulfur-containing amino acids. The metal ions associated with partial lectin activity are often Ca ²⁺ and Mg ²⁺ , which are necessary for many sugars to bind or agglutinate. An essential condition for the aggregation of many lectins (such as C-type lectins) is the presence of Ca ²⁺ . In lectin (Limulin), C expansion + calcitonin-like physiological activity is required; in Anthocidariscr assispina, Ca ²⁺ affects the molecular configuration of lectin: Ca ²⁺ affects oyster lectin through Change protein configuration instead of directly participating in ligand binding. Some people think that Ca ²⁺ interacts with sulfonyl groups through ionic bonds to stabilize the structure and enhance the interaction between hydrogen bonds and hydrophobic groups.

The lectin agglutination reaction is often inhibited by monosaccharides, and some require some disaccharides, trisaccharides or polysaccharides, and the sensitivity of inhibition is quite different. Some typical specific lectins are easily inhibited by some sugars in the corresponding blood group substances, such as type A blood antigen specific lectins are suppressed by N-acetyl-D galactose; type O specific lectins are blocked by L-fucose Suppressed. The specificity of lectin-binding sugars varies. The binding range of a few lectins is quite narrow. Mild treatment of lectins with proteases, such as trypsin and streptomycin, can increase the sensitivity of their agglutination activity, and some additives and metal ions also affect the lectin activity.

Significance of lectin research

Lectins are widely present in animals and plants. The biggest feature of lectins is the ability to recognize complex carbohydrate structures in glycoproteins and glycolipids, especially in cell membranes, that is, the glycosyl groups on the surface of cell membranes. A lectin has the ability to specifically bind to only one specific glycosyl group. Therefore, lectins can be used as probes to study the structure of cell membranes. Lectin has a variety of biological activities in the blood of invertebrates. It can choose to agglutinate various cells and have specific agglutination effect on tumor cells. It is one of the important humoral factors of immune defense. On the other hand, lectin has multivalent binding ability, can bind to fluorescein, enzymes, biotin, ferritin, and colloidal gold without affecting its biological activity, and can be used for immunocytochemical research at the light or electron level. It has certain value in exploring the biological evolution process of cell differentiation, proliferation, and malignancy, showing tumor-associated antigens, and diagnostic evaluation of tumors. In addition, phytohemagglutinin also plays a very important role in plants, such as the role in seed germination; as a mitogenic factor for plant embryo cells; and for its protective function in crop pest control. Studying the specificity of lectins helps to understand life phenomena or pathological changes at the molecular or atomic level ^[3] .