Lectin: Application & Overview

Lectin: Overview

Lectins are carbohydrate-binding proteins that recognize and reversibly bind the carbohydrate moieties of complex glycoconjugates. Their molecular interaction with sugar groups does not affect the covalent structure of any recognized glycosyl ligands. 

Lectins are ubiquitous and prevalent in almost all plants, animals, and microorganisms. Depending on the amounts of lectins present and the type of carbohydrates bound to them, lectins can be of different types in different organisms.

The protein is also considered an “anti-nutrient” because it interferes with digestion. Though some lectins are safe, some pose health risks in humans. The types of high-lectin foods that have dangerous health effects include peanuts, whole grains, raw kidney beans or red kidney beans, raw potatoes, lentils, wheat germ, and raw soybeans. For people more sensitive to lectins, it’s recommended to have a lectin-free diet.

To reduce the negative effects of lectin content in foods, such as legumes, grains, and nightshade vegetables, you need to cook, ferment, or sprout these lectin-containing foods. Lectins like CLEC11A are ones with health benefits, while some lectins, such as ricin, display dietary toxicity in consumers.

The effects of lectins on human health are mainly due to the way it binds to carbohydrate or sugar groups of molecules. However, the specificity of the molecule to sugar moiety has diverse applications in many labs and industrial processes. 

For example, in clinical labs, it’s used to analyze blood type, and in research labs, it has applications in transferring pest resistance to genetically engineered crops.

In this article, we teach you the binding mechanism of lectins, their functions, and their applications in pharmaceutical, health, and research sectors.

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How Does Lectin Work?

Lectins have one non-catalytic domain, having the ability to reversibly bind to specific monosaccharides or oligosaccharides. They bind to sugar groups of the molecules, especially on the surface of erythrocytes, without changing their structural properties.

Based on the binding affinity of lectins to specific carbohydrates, they are classified into the following groups:

  • complex type N-glycan specific lectins
  • High mannose type N-glycan specific lectins
  • Both above type N-glycan specific lectins,

However, they are also classified based on the number of carbohydrate-binding sites and the structure and evolution of the molecule in organisms.

Figure: The representation of the classification of lectins based on different properties.

Dietary Lectins

Humans can’t digest lectins. Most of the time, the molecule just passes through our digestive system unchanged, without effect by digestive enzymes. While some lectins don’t affect us, some of them, when consumed too much, can also have health effects. 

The symptoms caused by the toxin type of lectins (such as phytohaemagglutinin or PHA) include abdominal pain, diarrhea, vomiting, bloating, gastrointestinal problems, and nausea. Symptoms like these can be eased by consulting a registered dietitian, who can diagnose the cause and suggest a diet to remedy them.

Some lectins bind to the cell lining of the digestive tract and disrupt nutrient absorption. Some studies have shown lectins’ roles in triggering immune responses after binding to the intestinal walls of mammals. 

For example, some lectins that remain bound to cells for a longer period of time cause autoimmune diseases, such as rheumatoid arthritis, by developing antibodies against them. Some are also responsible for obesity and type 2 diabetes.

Though it might seem to you that lectins have more negative effects. However, lectin-rich foods, like quinoa, bell peppers, and nuts, are a great source of Vitamin B, minerals, fiber, antioxidants, and other nutrients. Some plant lectins also aid in weight loss and lower the incidence of heart diseases. 

What is Lectin Used For?

Lectin has a range of roles in the pharmaceutical, medical, and research industries. Have a look at some of their applications below.

Affinity Chromatography

Lectins are frequently used in affinity chromatography workflows. They are immobilized on gel beads and absorb glycoproteins, which are later eluted using a specific carbohydrate. 

Further, serial lectin column chromatography is used to isolate glycoproteins present in a very small concentration. Lectin is also used in combination with other separation techniques to purify oligosaccharides.

Pathogen Control

Lectin has anti-fungal and anti-insect activities that are exploited to control pathogens. For example, Gastrodia elata lectins are expressed in vascular cells of stems and roots against the fungus Trichoderma viride, defending plants against such diseases.

Anti-Tumor Drugs

Lectins treat cancer by eliciting apoptosis (cell death) in cancer cell lines. For example, B16-BL6 melanoma cells are cured using Korean mistletoe lectin. Similarly, Dark red kidney bean hemagglutinin shows antiproliferative activity toward leukemia L1210 cells, and Glycine max lectin obstructs the proliferation of breast cancer MCF7 cells.

Antiviral Drugs

Lectins are used as antiviral drugs to treat some viral diseases. For example, a d-mannose-specific lectin from Gerardia savaglia has been found to prevent human immunodeficiency virus (HIV)-1 infection of H9 cells. Similarly, some plant lectins, such as mannose-binding lectins, show anti-coronal activity in severe acute respiratory syndrome coronavirus.

What Industries Use Lectin? 

The specificity of lectins for a range of carbohydrates has a myriad of applications in the pharmaceutical, healthcare, biotechnology, and research sectors. 

Food & Beverage

Lectins are present in a variety of plant foods. It’s present in soy products, green peas, legumes, lentils, and chickpeas. These foods are rich in nutrients, minerals, fibers, and vitamins. However, they are rarely eaten raw. Most of them are consumed either soaked, cooked, or sprouted.

Healthcare

Lectin-rich foods are a rich source of antioxidants and prevent an increase in blood sugar levels by slowing down carbohydrate absorption in the body. Many studies have shown that foods like whole grains and nuts have a major association with weight loss and lower the risks of type-2 diabetes and cardiovascular diseases.

Pharmaceutical 

The binding affinity of lectins with sugar moieties of molecules is used in many research and pharmaceutical sectors. It’s mainly exploited to isolate a particular molecule using affinity chromatography or manufacture drugs to treat many pathological conditions, like cancer and viral diseases.

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Lectins are proteins having high specificity for carbohydrates or sugar moieties of the molecules. They are also often referred to as agglutinin since they agglutinate some particular cells and precipitate polysaccharides and glycoproteins. Lectins are of different types based on the type and number of carbohydrates they bind to. They are present in almost every organism, ranging from plants to animals, and microbes. 

We consume some lectins in the form of plant food. However, many of these, such as phytohaemagglutinin (PHA — having high lectin activity), have negative health effects. Some lectins also provide health benefits when consumed after being soaked, sprouted, or cooked. 

The affinity of lectins for carbohydrates is exploited in many pharmaceutical and medical industries to manufacture drugs to treat diseases or develop their diagnosis. Researchers use lectin to perform high-throughput techniques like affinity chromatography for the isolation of specific molecules.

However, to conduct such advanced assays, one requires high-quality chemicals and equipment to obtain verified data and accurate results. Thus, the process can become expensive and hinder researchers’ lab processes.

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