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The secret of chemical bonds: How do antigens and antibodies achieve precise binding through weak interactions?
The interaction between antigen and antibody is a special chemical reaction, a process caused by the in-depth interaction between antibodies and antigens produced by B cells in white blood cells. This specific bonding process is called coagulation. It is the basic reaction of our body to resist foreign pathogens and their toxins. In the blood, antigens bind to antibodies with high affinity and specificity, forming antigen-antibody complexes and are subsequently transported to the cellular system for easy removal or inactivation.
This theory has been called the "Goldberg Theory" since Richard J. Goldberg first correctly described the antigen-antibody reaction at the University of Wisconsin in 1952.
There are many types of antibodies and antigens, and each antibody can only bind to a specific antigen. The reason for this specificity is the specific chemical structure of the antibody. The antigenic determinant or epitope of an antigen is recognized by the binding site of the antibody, which is located in the variant region of the polypeptide chain. These variant regions themselves have hypermutation regions, which are a series of unique amino acid sequences, and all types of antibodies are different. The binding between antigen and antibodies is mainly achieved through various weak non-covalent interactions such as electrostatic, hydrogen bonding, van der Waals forces and hydrophobic interactions.
Molecular basis of immunity
The immunity produced by an individual when exposed to an antigen is called acquired immunity. In contrast, the immunity that exists at birth is called innate immunity. Acquired immunity relies on the interaction between an antigen and a group of proteins called antibodies that are produced by B cells in the blood. Each antibody is specific to a specific type of antigen, so the immune response of acquired immunity stems from the precise binding between the antigen and the antibody.
In the antibody structure, the antigen binding fragment (Fab) is composed of the amino terminus of the light and heavy chains of the immunoglobulin polypeptide. The variant domain of this region consists of amino acid sequences that determine the binding affinity of the antibody type to its antigen. The binding sequences of variant light chains (VL) and variant heavy chains (VH) form three hypermutation regions (HV1, HV2, HV3), which are the main parts of antibodies' recognition and binding to antigens.
Chemical basis of antigen-antibody interaction
The binding of antibodies to antigens is primarily dependent on weak chemical interactions, which are essentially non-covalent. Depending on the specific part of the interaction, the involved effects include electrostatic, hydrogen bonding, van der Waals forces and hydrophobic interactions. Non-covalent binding between antibodies and antigens may also be helped by interface water molecules, and these indirect bindings promote cross-reactions, i.e., the recognition of different but related antigens by a single antibody.
Properties and affinity of antibodies
The interaction between the antigen and the antibody shows high affinity, similar to the binding of the lock and key. There is a dynamic equilibrium in this process, where the reaction is reversible. The evaluation of affinity and affinity can be achieved through dissociation constants. The lower the dissociation constant, the higher the affinity or affinity, and the stronger the binding strength.
Challenges of Autoimmune Diseases
Under normal circumstances, antibodies can distinguish between external molecules and internal molecules produced by cellular activities, and remain silent to their own molecules. But in some cases, antibodies recognize their own molecules as antigens, triggering unexpected immune responses, leading to different types of autoimmune diseases. These diseases are often extremely harmful and even fatal.
Application of antigen-antibody interaction
Antigen-antibody interactions are widely used in laboratory techniques for hemocompatibility testing and diagnosis of various pathogenic infections. The most basic application is to determine the ABO blood type, which is very important for blood transfusion. More complex applications include enzyme-linked immunosorbent assay (ELISA), immunospot technology, and immunoelectrophoresis.
Through these methods, scientists can further study the mechanisms of disease and promote the development of vaccines and treatments. In potential applications, can future research explore the deeper mysteries between antigens and antibodies?
