What is the Difference Between Linear and Conformational Epitope

Linear and conformational epitope are two types of epitopes based on structure and interaction with the paratope of antibodies. An epitope is also known as an antigenic determinant. It is the part of an antigen that is recognized specifically by antibodies, B cells or T cells. Therefore, epitope is capable of stimulating an immune response.

The key difference between linear and conformational epitope is their structure. Linear epitope has a linear sequence of amino acid or continuous sequence of amino acids which will be recognized by the paratope of the antibody or receptor while conformational epitope has a discontinuous sequence of amino acids which will be recognized by the paratope of the antibody receptor.

CONTENTS

1. Overview and Key Difference
2. What is Linear Epitope
3. What is Conformational Epitope
4. Similarities – Linear and Conformational Epitope
5. Linear vs Conformational Epitope in Tabular Form
6. Summary – Linear vs Conformational Epitope
7. FAQ: Linear and Conformational Epitope

What is Linear Epitope?

Linear epitope contains linear sequence residues of amino acid or continuous sequence residues of amino acids (primary structure), which will directly interact with the paratope of the antibody (receptor). This amino acid sequence of linear epitope can be easily recognized by the antibody as there are no gaps between the amino acids sequence of epitope. The amino acids sequence of linear epitope does not undergo folding.

Figure 01: Linear Epitope

Furthermore, if a protein sample is boiled, treated with beta-mercaptoethanol, and run in SDS-PAGE for the western blot, linear epitopes are preferred for such studies. This is because the proteins are denatured in SDS-PAGE and cannot assume their natural three-dimensional conformations.

What is Conformational Epitope?

Conformational epitope contains discontinuous sequence residues of amino acids, which will be recognized by the paratope of the antibody (receptor). By using this sequence, conformational epitope will get bind over to the antibody. The amino acids sequence of conformational epitope is not easily recognized by the antibody as this sequence is discontinuous and has gaps between the amino acids. Because of this, amino acid sequence of conformational epitope undergoes folding in order become linear. After folding, this sequence acquires the ability to bind with the antibody easily.

Figure 02: Conformational Epitope

Most antibodies recognize a conformational epitope that has a specific three-dimensional shape or tertiary structure. Furthermore, in immunohistochemistry studies, conformational epitopes are preferred. This is because the protein structure is preserved so that antibodies can easily recognize the conformational epitopes.

Similarities Between Linear and Conformational Epitope

1. Linear and conformational epitope are two types of epitopes based on structure and interaction with the paratope.
2. They are made up of amino acids sequences.
3. Both types can bind to B cells.
4. Both types have numerous benefits in immunological industry.

Difference Between Linear and Conformational Epitope

Definition

1. A linear epitope is an epitope that is recognized by antibodies by its linear sequence of amino acids.
2. A conformational epitope is an epitope that is recognized by antibodies by its specific three-dimensional shape or discontinuous sequence of amino acids.

Commonness

1. Linear epitopes are less common.
2. Conformational epitopes are more common.

Binding

1. Linear epitopes bind to both B cells and T cells.
2. Conformational epitopes bind only to B cells.

Presence of Gaps

1. Linear epitopes do not have gaps between amino acid sequences.
2. Conformational epitopes have gaps between amino acid sequences.

Recognition by Antibodies

1. Linear epitopes are easily recognized by the antibodies.
2. Conformational epitopes are not easily recognized by the antibodies.

Folding

1. Linear epitopes do not undergo folding.
2. Conformational epitopes undergo folding.

Significance

1. Linear epitopes are preferred in SDS-PAGE and West blot studies.
2. Conformational epitopes are preferred in immunohistochemistry.

The following table summarizes the difference between linear and conformational epitope.

Summary – Linear vs Conformational Epitope

Epitope is the part of an antigen that is recognized by the antibodies, B cells, or T cells. Paratope is the part of an antibody that binds to the epitope. Based on structure and interaction with the paratope, epitopes are two types as linear and conformational epitope. Linear epitope contains linear sequence of amino acid or continuous sequence of amino acids which will be recognized by the paratope of the antibody. Conformational epitope contains discontinuous sequence of amino acids which will be recognized by the paratope of the antibody. Furthermore, linear epitope can bind to both B cells and T cells while conformational epitope can only bind to B cells. This is summary of the difference between linear and conformational epitope.

FAQ: Linear and Conformational Epitope

1. What are epitopes and paratopes?

• The part of an antibody that binds to the epitope is called a paratope. An epitope is the part of an antigen that is recognized by the immune system. A single paratope can bind to unrelated epitopes, and a single epitope can bind to unrelated paratopes.

2. What is the smallest epitope?

• Typically, epitopes of antigens are about 12 to 20 amino acids in length. The smallest epitope, which have been mapped so far, comprises only three amino acids and part of the adjacent peptide bond.

3. How does one classify epitopes?

• Most commonly, epitopes are classified as either continuous or discontinuous, depending on whether the residues involved in the epitope are contiguous in the polypeptide chain, or not. Based on this, there are two types of epitopes: linear (contains continuous amino acid sequence) and conformational epitope (contains discontinuous amino acid sequence).

4. What is the significance of a linear epitope?

• In SDS-PAGE and western blots studies, linear epitopes are preferred. This is because the proteins are denatured in SDS-PAGE and cannot assume their natural three-dimensional conformations.

5. What is the significance of a conformational epitope?

• Immunohistochemistry is a laboratory method that uses antibodies to check for certain antigens in a sample of tissue. In immunohistochemistry studies, conformational epitopes are preferred. This is because protein structure is preserved and antibodies can easily recognize conformational epitopes.

Reference:

1. “Linear Epitope – An Overview.” ScienceDirect Topics.
2. Lo, Ying-Tsang, et al. “Conformational Epitope Matching and Prediction Based on Protein Surface Spiral Features.” BMC Genomics, U.S. National Library of Medicine.

Image Courtesy:

1. “Schematic diagram showing Polyclonal Response by B cells against Linear Epitopes” By KC Panchal – Own work (Public Domain) via Commons Wikimedia

2. “Epitope-mapping illustration-6-copy” By Kathryn Edmondson (as employee of Integral Molecular) – Own work (CC BY-SA 4.0) via Commons Wikimedia

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