The sweet “coat” of life

There is a sweet “coat” on the cell surface, and if it can be completely deciphered, we will be able to usher in a new chapter in medicine.

When it comes to sugar, you may think of colorful candy, or granulated sugar, brown sugar, etc. But what you may not know is that the surface of every cell in our body is covered with sugar. This sugar is a kind of polysaccharide, which is a long chain composed of many monosaccharide molecules. In addition to participating in many life activities in the human body, polysaccharides are also associated with many health problems, including AIDS, autoimmune diseases and cancer.

The structure of polysaccharides is very complicated, but the researchers believe that analyzing the location and structure of polysaccharides on each cell can help doctors diagnose and treat their patients, and will lead us into a new era of modern medicine.

“coat” on the cell

Proteins, nucleic acids (DNA and RNA) and polysaccharides are the three main types of biological macromolecules. They are very different, but they all work closely together to participate in life processes. Among them, DNA determines our appearance, our thinking and behavioral ability, and even our most susceptible diseases. There are many short fragments in the DNA strand, usually containing instructions on how to synthesize proteins, which are genes. Protein is the “worker who is working hard” and participates in every process of cell life activity.

Most of the polysaccharides adhere to the protein and fat of the cell membrane, and together they form a thick layer of sugar coating outside the cell. In fact, if you can see a cell with the naked eye, it looks like a small ball full of fluff, which is a polysaccharide.

These polysaccharides can greatly affect the way proteins work on the cell membrane and even affect the behavioral response of the entire cell. For example, if you change some of the polysaccharides on your cells, this may cause the cells to migrate to different locations in our body.

The sugar coating of the cells also determines how the cells interact with the outside world. Every cell in our body has a unique sugar coating. Anything that wants to enter the cell, it must be able to identify which sugar coating it is, and use the right way to grab the sugar coating before it can enter. This is a bit like climbing, you have to have the right tools to grab the rock and you will be able to climb.

One of the most typical examples is the fertilization process. When the sperm arrives at the egg, it will encounter a transparent band. This is the thick icing that wraps the egg. Only the surface of the sperm cell has the right molecular tool to grasp the icing. The sperm has the opportunity to drill into the egg.

However, some pathogens can use polysaccharides to help them infect human cells. Deadly viruses like HIV and Ebola have evolved to have the ability to capture specific polysaccharides, and when they invade the human body, they can quickly “lock” the human cells that need to be infected. However, this provides a way to treat diseases such as AIDS: these viruses and the polysaccharides on the cells do not work to prevent these viruses from invading the cells. Now researchers are working hard to achieve this treatment.

Polysaccharide and immune system

Polysaccharides can also directly affect the immune system. We already know that every cell has a unique sugar coating. For example, the sugar coating of kidney cells looks different from the sugar coating of immune cells, but there are similarities between them. In fact, the immune cells in our body usually do not attack our own cells in our body, because the sugar coatings of all the cells in our body have many similar polysaccharides to indicate that they belong to the human body.

In contrast, bacteria and parasites are coated with sugar coatings that are completely different from human cells. When they invade the body, the immune cells of the body mark them as “foreign objects” according to their sugar coatings and attack them. However, some bacterial pathogens, such as group B streptococci (which usually cause severe infections in infants), can disguise adult somatic cells by carrying sugar-like coats similar to human cells, like wolves in sheepskins, to avoid being detected by the body’s immune system. , thus endangering the human body.

New research has also shown that some autoimmune diseases, such as rheumatoid arthritis and autoimmune pancreatitis, are also inextricably linked to polysaccharides. Normally, our immune cells act as a “defense system” in our body, and they secrete antibodies (a large protein) that recognize and destroy foreign invaders such as harmful bacteria or viruses. However, when the immune cells “stunned”, they produced the wrong antibodies, and the normal cells in the body became enemies, causing abnormal inflammatory reactions or tissue damage, which in turn affected the health of the body and caused diseases. The antibodies are also covered with polysaccharides, which directly affect the antibody’s ability to attack.

In addition, polysaccharides in food can also cause an immune response. For example, many studies have shown that if you regularly eat red meat (specially referred to as meat from mammals), it can cause chronic inflammation in the body. What is the reason? Until recently, scientists have figured out that the culprit is a polysaccharide called N-glycolylneuraminic acid, referred to as Neu5Gc. Neu5Gc is present in all mammals, but humans alone, probably because early humans who could produce Neu5Gc died of an ancient malaria.

However, although we now lack the ability to produce Neu5Gc, if we obtain this polysaccharide by eating red meat, our body “weaves” it into the sugar coating on the cells of the body. But our immune system recognizes Neu5Gc and attacks cells containing this polysaccharide as foreign objects. Therefore, when eating red meat every day, this is equivalent to a continuous inflammatory reaction in the body. Such chronic inflammation can increase the risk of atherosclerosis, type 2 diabetes, coronary heart disease, and diseases such as rectal cancer, pancreatic cancer, and lung cancer. .

Analysis of polysaccharides is extremely challenging

In summary, polysaccharides are associated with many disease states. Researchers believe that in the future, doctors may use polysaccharides to diagnose and treat diseases such as AIDS, rheumatoid arthritis, food allergies, and cancer. To achieve this, researchers need to analyze the structure of the polysaccharides on each cell in the human body and where they are attached. However, analyzing polysaccharides is a very challenging task.

The structure of polysaccharides is much more complicated than DNA. The DNA consists of only four bases (A, T, G, C) in a single line, but the polysaccharide is composed of dozens of different monosaccharides, and they are combined into a complex and variable branch structure. Analysis of polysaccharides is not just about analyzing which monosaccharides it consists of, but also how these monosaccharides are combined. In addition, each cell has the same genome, but the sugar coating on each cell is different, which undoubtedly increases the task of analyzing polysaccharides.

But this scares the researchers. At the end of 2018, Richard Cummings of Harvard Medical School in the United States and Gordon Laugh of the University of Zagreb in Croatia jointly created the “Human Polysaccharide Group Program”, which plans to analyze all the polysaccharides in the human body. . Researchers are developing rapid and reliable methods for analyzing human polysaccharides, and hope to understand their relationship with various diseases in the near future to help doctors diagnose and treat various diseases. In short, as we gradually decipher the sweet “coat” of life, a new chapter in medicine is about to open.