Antibody- Structure, Classes and Functions. Antibodies are heavy (~ kDa) globular plasma proteins. The basic structure of all antibodies. Structural Biology and Functions of Immunoglobulins. 1 Immunoglobulin Structure-Function Relationship Outline of Lectures; 3. Cell. Antibody molecules have a common structure of four peptide chains. This structure consists of two identical light (L) chain polypeptide of about.
In H-chain, one domain is found in Variable region VH. Fab region Antigen binding is accomplished by amino-terminal N-terminal region and effector functions by carboxyl terminal C-terminal region of antibody. In an antibody molecule two Fab regions are found and they binds antigens. Detailed comparison of aminoacids sequences of large number of VL and VH domain reveals that the sequence variation is concentrated in few discrete region of these domains.
- Antibody- Structure, Classes and Functions
- Describe how the structure of an antibody is related to its function?
The variability plot of VH and VL domains shows maximum variation in certain region which is known as hypervariable region and this forms antigen binding site. Antigen binding site is complementary to epitope of antigen, so it is also known as complementary determining regions CDRs. Fc region of immunoglobulin allows for interaction of immune complex with other phagocytic cells and complement.
Take parts in various biological functions that are determined by aminoacid sequences of each domains of constant region. Many different form of Fc receptors exists. Hinge region is rich in proline residue and is flexible.
Antibody: Structure, classes and functions
Hypervariable HVR or complementarity determining regions CDR Comparisons of the amino acid sequences of the variable regions of immunoglobulins show that most of the variability resides in three regions called the hypervariable regions or the complementarity determining regions as illustrated in figure 3.
Antibodies with different specificities i. CDR is the antibody combining site. Complementarity determining regions are found in both the H and the L chains. Framework regions The regions between the complementarity determining regions in the variable region are called the framework regions figure 3.
There was a problem providing the content you requested
Based on similarities and differences in the framework regions the immunoglobulin heavy and light chain variable regions can be divided into groups and subgroups. These represent the products of different variable region genes.
Fab Digestion with papain breaks the immunoglobulin molecule in the hinge region before the H-H inter-chain disulfide bond Figure 4. This results in the formation of two identical fragments that contain the light chain and the VH and CH1 domains of the heavy chain.
Antigen binding - These fragments were called the Fab fragments because they contained the antigen binding sites of the antibody. Each Fab fragment is monovalent whereas the original molecule was divalent. The combining site of the antibody is created by both VH and VL. An antibody is able to bind a particular antigenic determinant because it has a particular combination of VH and VL. Different combinations of a VH and VL result in antibodies that can bind a different antigenic determinants.
Fc Digestion with papain also produces a fragment that contains the remainder of the two heavy chains each containing a CH2 and CH3 domain. This fragment was called Fc because it was easily crystallized.
Effector functions - The effector functions of immunoglobulins are mediated by this part of the molecule. Different functions are mediated by the different domains in this fragment figure 5. Normally the ability of an antibody to carry out an effector function requires the prior binding of an antigen; however, there are exceptions to this rule.
F ab' 2 Treatment of immunoglobulins with pepsin results in cleavage of the heavy chain after the H-H inter-chain disulfide bonds resulting in a fragment that contains both antigen binding sites figure 6. This fragment was called F ab' 2 because it is divalent.
Describe how the structure of an antibody is related to its function? | MyTutor
The Fc region of the molecule is digested into small peptides by pepsin. The F ab' 2 binds antigen but it does not mediate the effector functions of antibodies.Immunology - Antibody Structure & Function
In this view, the HV regions of the Fab have been deleted. The FR regions of the antibody do not contact the antigen. This ribbon structure shows the antibody's HV purple and FR yellow regions of the Fab, and their interaction with an epitope of the antigen. In hen egg white lysozyme, a glutamine at position Gln protrudes away from the antigen surface. In this view, Gln is circled. The antibody is not shown. The following images show how this feature is important for the formation of a high affinity antibody-antigen interactions.
Antibody- Structure, Classes and Functions
The antibody's HV region forms an opening to surround the antigen's protruding Gln green. Hydrogen bonds yellow stabilize the antibody-antigen interaction.
In addition to hydrogen bonds, other weak interactions such as van der Waals forces, hydrophobic interactions and electrostatic forces improve the binding specificity between antibody and antigen.