antibody structure and function Flashcards
why are antibodies also called globular proteins and immunoglobulins?
because they are large glycoproteins based on their tertiary and quaternary structure have globular confirmation
what is the simplest antibody composed of?
4 peptide chains with an amino and carboxyl end bound together by disulfide bonds
what are the Fab regions of the antibody?
amino ends of the polypeptide sites
what is in the Fc region of the antibody?
carboxyl ends of the peptides
what are the two forms of light chains?
lambda and kappa ends
true or false: Since the chains are identical on an antibody molecule, an antibody will contain either forms of the light chains
true
what proteolytic enzyme was Porter working with?
papain
what does papain chemically digest an antibody molecule into and the significance of it?
3 proteins
Two of them were able to still bind antigen epitope and labeled them Fragment antigen binding (Fab) and the last could be crystalized out of solution (Fc).
what can digest the antibody molecule in to a divalent fragment (F(ab’)2) and numerous Fc
smaller fragments?
endopeptidase pepsin
what part of the antibody determines the antigenic epitope specificity of each antibody?
the 2 light polypeptide chains and 2 heavy polypeptide chains of the V regions
what impacts the structural conformation of the regions of 2 light polypeptide chains and 2 heavy polypeptide chains (V regions)?
they have a high degree of variability of amino acid sequences
true or false: for each antibody the 2 heavy
polypeptide chains and the 2 light chains are different to each other.
false: identical
why is the C region called the constant regions?
the light polypeptide chains and heavy chains contain relatively conserved amino acids for the individual
what is the purpose of the hinge region?
provide flexibility to the antibody molecule aiding in its function
antibodies can be bound to the surface of B cells as a component of the B cell receptors (BCR) coupled with a ____________________________ to form the B cell receptor complex
surface heterodimer protein Igα/Igβ
when antibodies exist as a secretory protein, where can they be found?
secretions, intracellular spaces, and blood vascular
true or false: each antibody has specificity for a particular antigenic epitope
true
what is the specificity of the antibody conserved for?
all the BCRs on that specific B cell and all the antibodies that are produced by that specific B cell
what is the hypervariable regions of the antigen-antibody binding (Fab) region?
complimentary determining regions (CDRs) in which the amino acids in these regions are unique per antibody
what is the result of the substitution of the amino acids in the CDR?
alter the structural conformation of the antibody binding site and thus, the antigenic epitope that it can recognize
what solely defines the conformational groove that recognizes a specific epitope structure?
based on the interaction between the amino acid sequences in the hypervariable regions or CDRs of the heavy chain with the CDRs of the light chain
what is the outcome of the hypervariable region?
each naïve B cell can create an antibody with a
unique antibody binding site capable of recognizing a unique antigen epitope
what does the cysteine contain that forms the disulfide bonds between the peptide chains?
reactive sulfhydryl groups
the hinge region of the heavy chains allow for what?
flexibility for optimal binding to multiple antigens expressing the same epitope
what is the purpose of proline?
serves to prevent globular folding to contribute to diverse biological activity of the glycoprotein
since the Fc region is the site for the
biologic activities of the antibody molecule, in order to prevent premature biologic activity, the Fc region is folded in to the ____________________
secretory antibody
what happens once the secretory antibody binds antigenic epitope via antigen binding?
the antibody undergoes a confirmation
change causing the Fc portion to be position outward, similar to a flag so the antibody can participate in its designate biologic activity
what is the first step in order for antibodies to perform biological activity?
they first have to recognize their cognate antigen epitope and bind to it
what is agglutination?
crosslinking to create aggregates
ex. RBCs + antibody = agglutination
what is are examples of a diagnostic testing that uses the principle of agglutination?
- ABO blood typing test in humans
- coombs test used to evaluate hemolytic disease of newborn or immune-mediated hemolytic anemia
what is opsonization?
coating of antigen with secretory antibodies allowing it to be more efficiently phagocytosed
what makes the phagocytosis of the antigen more efficient in regards to the Fc region during opsonization?
upon binding to antigen epitope, the antibody molecule undergoes a conformational change allowing the Fc region to be fully extended allowing it to be bound by cells expressing a receptor (Fc receptor)
what is neutralization?
the process in which antibodies bind to an organism (i.e. flagella or cilia of a bacteria) or toxin (i.e. tetanus, botulinus, snake venom) and block its activity
what is an example of a diagnostic testing using neutralization?
virus neutralization assay- to detect the presence of host neutralizing antibodies
in patients to select viruses like COVID-19
what is precipitation?
process in which antibodies bind to soluble antigens causing them to clump and form a visible precipitate
how are precipitation and agglutination similar?
mechanism of action in that the antibodies cross link the epitopes on different antigens
what is the difference between precipitation and agglutination?
the target antigen is soluble and not particulate
what is an example of a diagnostic testing using precipitation?
immunodiffusion assays- to detect the presence of soluble antigen
what are complement proteins?
collection of innate proteins that are continuously produced in the body as they tend to degrade rapidly
what is the purpose of complement activation?
when the complement proteins are activated, they can significantly ramp up the immune response
true or false: some of the byproducts of complement pathways can function as opsonins
true
what is the result of antibodies (IgG) activating complement via classical pathway?
lysis of target cell
what does it mean when the CDRs in the VL and VH regions form the antigen-antibody binding site based the interaction of the amino acid residues?
the binding of epitope in the antigen groove (binding site) is weak and noncovalent
when the binding of an epitope is weak and noncovalent, what does this suggest?
weak binding could allow antibodies to be recycled
why does antigen epitope recognition and binding have to be tight?
it reinforces the concept of antigen specificity
What do the evaluation of antibody titers tell us about an individual?
it is a type of blood test that determines the presence and level (titer) of antibodies in the blood. This test is carried out to investigate if there is an immune reaction triggered by antigens in the body.
