What is the Difference Between Epitope and Paratope

The main difference between epitope and paratope is that epitope is a specific antigenic determinant that occurs on the antigen, whereas paratope is the antigen-binding site on the antibody. Furthermore, immune system components, including antibodies, B cells, and T cells, recognize epitopes while paratope binds to the specific epitope. 

Epitope and paratope are two types of binding regions found on proteins. They play an important function in the humoral immunity by means of recognition. 

Key Areas Covered 

1. What is an Epitope
     – Definition, Structure, Importance
2. What is a Paratope
     – Definition, Structure, Importance
3. What are the Similarities Between Epitope and Paratope
     – Outline of Common Features
4. What is the Difference Between Epitope and Paratope
     – Comparison of Key Differences

Key Terms

Antibody, Antigen, Epitope, Humoral Immunity, Paratope

What is an Epitope 

An epitope is a part of an antigen recognized by the immune system components, including antibodies, B cells, and T cells. It is also known as an antigenic determinant. In other words, an epitope is a specific part of an antigen to which the antibody binds. Generally, epitopes can be either self or non-self. Normally, the immune system triggers responses against non-self epitopes, but in autoimmune diseases, the immune system triggers responses against self-antigens. 

Figure 1: Epitopes

Furthermore, based on the structure and interactions, there are two types of epitopes: conformational epitopes and linear epitopes. Basically, conformational epitopes are formed by the interactions of discontiguous amino acid residues, while linear epitopes are formed by the interactions of contiguous amino acids.  

What is a Paratope 

A paratope is the part of an antibody that specifically binds to the epitope. Therefore, it is known as the antigen-binding site. Generally, it is a small region in the Fv region of the antibody. Moreover, the size of the paratope is 5-10 amino acids. Here, the Fv region is a part of the Fab or fragment antigen-binding region. Additionally, an antibody is a Y-shaped molecule. Therefore, both of the arms of an antigen contain Fv regions. 

Figure 2: Antibody Structure (1. Fab, 2. Fc, 3. heavy chain, 4. light chain, 5. antigen-binding site, 6. hinge regions)

However, the complementary binding of the heavy and light chain helps to produce the 3D structure of the paratope. Furthermore, mimotope is a macromolecule that binds to the paratope, mimicking the binding of an epitope. 

Similarities Between Epitope and Paratope 

• Epitope and paratope are two recognition sites found on proteins important for the immune system. 
• Both are important for the discrimination between self and non-self by the immune system. 
• They have compatible 3D structures for specific binding. 
• Moreover, both can help to trigger an immune response. 

Difference Between Epitope and Paratope 

Definition 

Epitope refers to the part of an antigen molecule to which an antibody attaches itself, while paratope refers to the part of the molecule of an antibody that binds to an antigen. Thus, this is the main difference between epitope and paratope.

Also Known as 

An epitope is also known as an antigenic determinant, while paratope is also known as an antigen-binding site.  

Occurs on 

Another major difference between epitope and paratope is that epitope occurs on both self or non-self antigens, while paratope occurs on antibodies. 

Binds to 

Epitope binds to the paratope on antibodies and receptors on both B and T cells while paratope binds to the epitopes. 

Function 

Moreover, epitope helps to discriminate between self and non-self, while paratope helps to recognize specific antigens to trigger a humoral immune response. 

Conclusion 

An epitope is an antigenic determinant occurs on antigens. However, these antigens can be either self and non-self. On the other hand, paratope is the structural part occurs on antibodies. Moreover, it recognizes epitopes specifically and helps to trigger a humoral immune response. Therefore, the main difference between epitope and paratope is their occurrence and importance. 

References:

1. “What Is an Epitope.” Pacific Immunology, Available Here.
2. “Paratope.” Paratope – an Overview | ScienceDirect Topics, Available Here.

Image Courtesy:

1. “Chem114A epitopes” By Tinastella at English Wikibooks – Transferred from en.wikibooks to Commons. (Public Domain) via Commons Wikimedia   
2. “Immunoglobulin basic unit” By Y_tambe – Y_tambe’s file (CC BY-SA 3.0) via Commons Wikimedia