Framework region

[4] To increase its stability, the framework region has less variability in its amino acid sequences compared to the CDR.

[5][6][7] Individual residues in the framework region can be divided into two categories, depending on whether they are in direct contact with the antigen.

[4] Framework residues that do not come in contact with the antigen affect the binding indirectly by aiding in structural support for the CDR.

This enables the CDR to take on the correct orientation and position so it is exposed on the surface of the chain ready to bind to an antigen.

[8] Natural mutations in the variable region are typically due to activation-induced cytidine deaminase (AID).

This somatic hypermutation allows for immunoglobulin class switching but also results in affinity maturation of the antibody.

The universal structure of antibody includes the constant regions part of the fragment crystallizable(Fc) region of the antibody (shown in dark blue). It also includes the fragment antigen binding which is composed of one heavy and one light chain (shown as L for light and H for heavy). Each heavy and light chain is composed of one variable region and one constant region (shown as V or C). The variable regions are composed of 7 amino acid segments; three of which are hypervariable regions or CDR (yellow) and four of which are FR(shown in green for heavy chains and pink for light chains).