Occurrence, structure and functions of heteroglycans- blood group substances and sialic acids

Blood Group Substances

  • Occurrence: Blood group substances are glycoproteins and glycolipids found on the surface of red blood cells, epithelial cells, and other tissues.
  • Structure: They consist of oligosaccharides attached to proteins (glycoproteins) or lipids (glycolipids). The terminal sugars determine the blood group:
    • Type A: N-acetylgalactosamine (GalNAc) is added to the H antigen.
    • Type B: Galactose (Gal) is added to the H antigen.
    • Type AB: Both GalNAc and Gal are present.
    • Type O: No additional sugar is added to the H antigen.
  • Functions: These substances determine blood group compatibility in transfusions and play roles in cell recognition and immune responses. They are also involved in various physiological processes, such as microbial adhesion and signaling pathways.

Sialic Acids

  • Occurrence: Sialic acids are a family of acidic monosaccharides found at the outermost position of glycan chains on glycoproteins and glycolipids in animal tissues, especially in the brain and epithelial cells.
  • Structure: The most common form is N-acetylneuraminic acid (Neu5Ac), which can be modified by acetylation, methylation, or other modifications.
  • Functions: Sialic acids play crucial roles in various biological processes, including:
    • Cell-Cell Interaction: They mediate interactions between cells and the extracellular matrix.
    • Immune Response: Sialic acids are involved in immune recognition and protect cells from complement-mediated lysis.
    • Microbial Pathogenesis: Many pathogens exploit sialic acids for cell entry and immune evasion.
    • Neural Development: Sialic acids are critical for brain development and function, influencing neurogenesis and synaptic plasticity.

Overview

Both blood group substances and sialic acids are critical components of heteroglycans with significant biological roles. Blood group substances are essential for determining blood compatibility and mediating immune responses, while sialic acids are involved in a wide range of cellular interactions and functions, from immune protection to neural development. Their structural diversity and specific modifications contribute to their unique functions in various physiological and pathological processes. 

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