Fragment antigen-binding region

Region of an antibody that binds to antigens

The fragment antigen-binding region (Fab) is a crucial part of an antibody that is responsible for binding to antigens. This region is essential for the immune system's ability to recognize and neutralize foreign substances such as bacteria and viruses.

Structure

Structure of a Fab fragment.

The Fab region is composed of one constant and one variable domain from each of the heavy and the light chains of the antibody. The variable domains contain the complementarity-determining regions (CDRs), which are responsible for the high specificity of antigen binding. The Fab region is connected to the Fc region of the antibody via a flexible hinge region, allowing for movement and better antigen binding.

Function

Diagram of an antibody showing the Fab and Fc regions.

The primary function of the Fab region is to bind to specific antigens. This binding is highly specific due to the unique structure of the CDRs, which can recognize and bind to specific epitopes on the antigen. Once bound, the Fab region can neutralize the antigen directly or mark it for destruction by other components of the immune system.

Applications

Fab fragments are used in various biotechnology and therapeutic applications. They can be produced by enzymatic digestion of antibodies or through recombinant DNA technology. Fab fragments are smaller than whole antibodies, which allows them to penetrate tissues more easily and be cleared from the body more rapidly. This makes them useful in diagnostic imaging and as therapeutic agents in conditions where rapid clearance is beneficial.

Production

Diagram showing the separation of Fab and Fc regions.

Fab fragments can be generated by treating antibodies with the enzyme papain, which cleaves the antibody above the disulfide bonds in the hinge region, resulting in two Fab fragments and one Fc fragment. Alternatively, recombinant DNA technology can be used to produce Fab fragments in bacterial or mammalian cell cultures.

Comparison with Other Antibody Fragments

Diagram showing F(ab')₂ and pFc' fragments.

In addition to Fab fragments, antibodies can also be cleaved to produce F(ab')₂ fragments, which contain two Fab regions linked by disulfide bonds, and pFc' fragments, which are part of the Fc region. Each of these fragments has distinct properties and applications in research and medicine.

Related pages

• Antibody
• Antigen
• Fc region
• Complementarity-determining region