variable region

antibody structure

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July 16, 2026

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The variable region of an antibody is a key component of its structure, responsible for recognizing and binding to specific antigens. Antibodies, also known as immunoglobulins (Ig), are proteins produced by the immune system to combat foreign substances.12

The basic structure of an antibody molecule is a flexible Y-shape, formed by four polypeptide chains: two identical heavy (H) chains and two identical light (L) chains. Each chain consists of constant (C) and variable (V) regions. The variable regions of both the heavy and light chains combine to form the antigen-binding site at the tips of the Y-arms.1

These variable regions have unique amino acid sequences that differ among antibodies, allowing each antibody to bind to a specific part of an antigen, called an epitope. This variability is crucial for the immune system's ability to recognize and neutralize a vast array of foreign invaders.12

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immune system
Basic structure of the immunoglobulin molecule
…regions, called constant (C) and variable (V). These regions are distinguished on the basis of amino acid similarity—that is, constant regions have essentially the same amino acid sequence in all antibody molecules of the same class (IgG, IgM, IgA, IgD, or IgE), but the amino acid sequences of the variable…
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…regions, called constant (C) and variable (V). These regions are distinguished on the basis of amino acid similarity—that is, constant regions have essentially the same amino acid sequence in all antibody molecules of the same class (IgG, IgM, IgA, IgD, or IgE), but the amino acid sequences of the variable…
Read More