Sialic acid is a generic term for a family of acidic sugar molecules that are often found at the outermost ends of glycan chains on the surface of animal cells and in some bacteria. These molecules are typically present in glycoproteins, glycolipids, and proteoglycans. Sialic acids play crucial roles in various biological processes, including cell-cell interactions, immune responses, and the recognition of self from non-self.
Sialic acid (SA), scientifically known as “N-acetylneuraminic acid”, is a naturally occurring carbohydrate. It was originally isolated from mucin in the submandibular gland, hence its name. Sialic acid is usually found in the form of oligosaccharides, glycolipids or glycoproteins. In the human body, the brain has the highest levels of salivary acid. The gray matter of the brain contains 15 times more salivary acid than internal organs such as the liver and lungs. The main food source of salivary acid is breast milk, but it is also found in milk, eggs and cheese.
Here are some key points about sialic acid:
Structural Diversity
Sialic acids are a diverse group of molecules, with various forms and modifications. One common form is N-acetylneuraminic acid (Neu5Ac), but there are other types, such as N-glycolylneuraminic acid (Neu5Gc). The structure of sialic acids can vary between species.
Cell Surface Recognition
Sialic acids contribute to the glycocalyx, the carbohydrate-rich layer on the outer surface of cells. This layer is involved in cell recognition, adhesion, and communication. The presence or absence of specific sialic acid residues can affect how cells interact with each other.
Immune System Modulation
Sialic acids play a role in immune system modulation. For example, they are involved in masking cell surfaces from the immune system, preventing immune cells from attacking the body’s own cells. Changes in sialic acid patterns can influence immune responses.
Viral Interactions
Some viruses exploit sialic acids during the process of infection. The viral surface proteins may bind to sialic acid residues on host cells, facilitating the entry of the virus into the cell. This interaction is seen in various viruses, including influenza viruses.
Development and Neurological Function
Sialic acids are crucial during development, especially in the formation of the nervous system. They are involved in processes such as neural cell migration and synapse formation. Changes in sialic acid expression can impact brain development and function.
Dietary Sources
While the body can synthesize sialic acids, they can also be obtained from the diet. For example, sialic acids are found in foods like milk and meat.
Sialidases
Enzymes called sialidases or neuraminidases can cleave sialic acid residues. These enzymes are involved in various physiological and pathological processes, including the release of newly formed virus particles from infected cells.
Research on sialic acids is ongoing, and their significance in various biological processes continues to be explored. Understanding the roles of sialic acids can have implications for fields ranging from immunology and virology to neurobiology and glycobiology.
Post time: Dec-12-2023
