Block B lecture 2 Flashcards
How were antibodies discovered ?
Late 19th century (Emil von Behring and Shibasaburo Kitasato): serum from animals immunised against diphtheria or tetanus toxins, you could transfer immunity from these animals to other animals.
Early 20th century: demonstration that something in immune serum could neutralise toxins, precipitate toxins, lyse bacteria and agglutinate bacteria.
1930s: realisation that all activities are due to one molecule - called “antibody” (or “immunoglobulin”)
1950s: antibody structure elucidated by Rodney Porter and Gerald Edelman
describe clonal selection theory in line with antibody production
Antibodies were shown to be produced by plasma cells that arise following activation of B lymphocytes (plasma cells) by Astrid Fagraeus in the late 1940s and by a mechanism involving clonal selection shown above, by Macfarlane Burnet and colleagues in the late 1950s. Each of the numbered cells in the diagram represents a lymphocyte with the different shapes on the surfaces corresponding to antibodies of different specificities. The antigen selects the antibody molecule on the surface of the lymphocyte that has the best ‘fit’ , like a lock and key. Binding of an antigen causes the cell to become active and undergoes clonal expansion to produce more cells that are identical to fit the infection
describe the structure of an antibody ?
Each antibody molecule is made up of two hinged heavy chains (green) and two light chains (yellow) joined by disulphide bonds so that each heavy chain is linked to a light chain and the two heavy chains are linked together. The region where the 2 heavy chains are linked is called the hinge region. The light chains are divided into 2 sections while the heavy chains are divided into 4 sections. These sections are each called an antibody domain.
how many classes of antibody are there ?
five antibody classes in humans and mice, which consist of one or more copies of this four-chain structure. These are called IgA, IgD, IgE, IgG and IgM and these vary in biological activities.
how many domains does the light chain have
2
heavy chain domains ?
4 in IgG , IgA , IgD and 5 in IgM and IgE
what does the antibody domains share similarities with ?
The antibody domain structure is found in many molecules of the immune system, e.g., the T cell receptor and accessory proteins, MHC molecules and adhesion molecules.
describe the constant and variable region in respect to amino acid sequence?
Each antibody chain has a constant and variable region with respect to amino acid composition. The constant regions show the same amino acid sequence while the variable regions show variability in the A.A sequence. The naming of individual domains reflects whether they are in the constant or variable region. Vh stands for the variable heavy domain , Vl is variable light domain and so on.
what does X ray crystallography show ?
A further schematic representation of an IgG antibody molecule denotes the angles that individual domains lie at, based on X-ray crystallography.
what does the protease papain cause in the Y shaped antibody ?
The Y-shaped antibody molecule can be cleaved by the protease papain at the hinge region to produce two Fab (fragment antigen binding) fragments and one Fc fragment. The Fab fragments contain the variable regions and bind antigen. Enzymes such as papain were used in the elucidation of the structure of the antibody molecule.
describe the hinge region ?
Antibody arms are joined by a flexible hinge. An antigen consisting of two homologous molecules (red balls in diagrams) that can cross-link two antigen-binding sites is used to create antigen: antibody complexes, which can be seen in the electron micrograph. Linear, triangular, and square forms are seen, with short projections or spikes. The interpretation of some of the complexes is shown in the diagrams.
What is the angle between the arms of the triangular forms ?
60 degrees
what is the angle between the square forms ?
90 degrees
are carbohydrates found in the antibodies ?
a small amount is found on all the antibodies
N linked ?
N linked it is bound via asparagine
O linked ?
O linked it is bound via serine.
what will the addition of carbohydrates to antibody cause ?
Addition of carbohydrate affects antibody secretion, if carbohydrates are removed then we cannot secrete antibody
Addition of carbohydrate affects antibody solubility, if carbohydrate decreases then so does the solubility of the antibody and precipitatation out a solution.
Addition of carbohydrate affects antibody catabolic rate.
describe hypervariability ?
There are discrete regions of hypervariability in antibody variable domains. The hypervariability regions of both the heavy and the light chain contribute to antigen binding of an antibody molecule.
what are the hypervariability regions called sometimes ?
more commonly termed: COMPLEMENTARITY-DETERMINING REGIONS (CDRS)
what are framework regions ?
Regions between CDRs are called framework (FR) regions
paratope ?
the CDRs that make up the antibody combining site constitute the PARATOPE
epitope?
the paratope is complimentary to the antigen-combining site, the EPITOPE
antibody domain ?
Antibody domains are barrel-shaped structures in which strands of polypeptide chain (beta strands) running in opposite directions (antiparallel) pack together to form two beta sheets, which are held together by a disulphide bond
antigen binding regions ?
hypervariable loops found at the end of the beta strands (red) are brought together to form antigen-binding regions.
what beings about the hypervariable loops ?
In a complete antibody molecule (lower panel), the pairing of a heavy chain and a light chain brings together the hypervariable loops from each chain to create a single hypervariable surface, which forms the antigen-binding site at the top of each arm. Because they are complementary to the antigen surface, the hypervariable regions are also commonly known as the complementarity-determining regions (CDRs). C, carboxy terminus; N, amino terminus.
what heavy chain is most important for antigen binding ?
heavy chain CDR3
