Antibody Fine Structure Flashcards
What does mercaptoethanol do? And why?
Breaks -S-S- bonds
To produce equal amounts of HEAVY and LIGHT chains
Weight of the light (L) chains?
~25kDa
Weight of the heavy chains?
~50kDa
How are the heavy and light chains bound?
By disulphide bridge
Does a disulphide bridge link the H chains or L chains?
H chains
Each H and L contains an amino-terminal variable (V) region. How many amino acids does it contain? And what do they differ in?
100-110 that differ from one antibody to the next
What is the remainder of each chain called?
Constant (C) region
Where are the amino and carboxyl ends of the antibody?
NH3+ at top
COO- at base
What are parts of the variable region called? And what are they?
Hypervariable or complimentarity-determining regions (CDRs)
3 on both H & L constitute the antigen binding site
What attaches to the C region?
Carbohydrates
What do some H chains contain?
(γ, δ, α) proline-rich hinge
What size of loops are formed by the folding of H & L?
60aa
How are effector functions mediated?
Constant domains
What are the classes of antibody?
IgG, IgE, IgD, IgA, IgM
How are the classes of Ig determined?
Kind of H chain
(γ, α, ε, δ, μ) = isotypes
What are the kinds of L chain?
κ and λ
Only 1 type for each Ab molecule, not both
Which classes are monomers? Dimers? And pentamers?
IgG, IgE, IgD are monomers
IgA is a dimer
IgM is a pentamer
What are IgA and IgM joined by?
J chain
What are the subclasses of IgA and IgG
IgA1 and IgA2 due to minor differences in H chain
IgG1-5
Ig fine structure is determined by organisation of the protein. What are the 1°, 2°, 3° & 4° structures?
1- aa sequence (V & C of H & L)
2- antiparallel β- pleated sheets
3- compact globular domains
4- interactive functional domains
What are conformational changes in antibody induced by?
Antigen binding
How are epitopes caught?
Loops (H1-3 & L1-3) in binding pocket MOVE to surround and capture the epitope
Is the movement of antibody arms dependent or independant?
Independant
Which Ig crosses the placenta?
IgG
Which Ig induces mast cell degranulation?
IgE
Which Ig is first to be produced in primary Ab response?
IgM - good agglutinator as pentamer
Which Ig has a secretory component?
IgA is protease resistant
Since Ig are glycoproteins, they can function as potent i——–
Immunogens
What does isotype describe?
(C region) describes Ig class and subclass is all members of the same species (eg IgG1 or IgM)
Allotypic determinants are?
Multiple alleles for some genes in H or L chain (between strains/ families within a species)
Idiotypic determinants are?
Idiotope= epitope in variable region, within or outside antigen binding site, different for each individual
What are immunoglobulins able to do?
Respond to a limitless array of antigens = 10^10 different antibodies each with its own specificity
How is C region maintained alongwith diverse V region?
2 theories
Germ-line theory (large repertoire of Ig genes in germ cells = eggs and sperm)
Somatic-variation theory (small number genes mutate/ recombine in somatic cell)
What is the diversity of antibodies due to?
Genomic rearrangement - shown only by lymphocytes
What happens as a B cell matures?
Gene segments are RANDOMLY SHUFFLED
this process is carefully regulated
After B cell matures, it contains chromosomal DNA that is no longer identical to what?
Grem-line DNA
What do V, J, D and C stand for (gene segments)
V Variable
D diverse
J joining
C constant
B cells exhibit ‘Allelic Exclusion’. What is it?
B cells contain both maternal and paternal chromosomes, but EXPRESS ONLY ONE for H and L chains
Somatic Hypermutation:
• Once a functional v………-r………. gene unit is formed it can be a……..! Occurs in g……….. c……….. during formation of memory B cells
•P………. s………. occurs once a……… interacts with membrane Ig, for those mutations that have increased a……….. of a………. (Affinity Maturation)
- Once a functional VARIABLE-REGION gene unit is formed it can be ALTERED! occurs in GERMINAL CENTRES during formation of memory B cells
- POSITIVE SELECTION occurs once ANTIGEN interacts with membrane Ig, for those mutations that have increased AFFINITY of ANTIBODY (Affinity Maturation)
What is Class/Isotype Switching? And what is it controlled by?
B cells can SWITCH Ig class, without loss of specificity
Controlled by T helper cell cytokines IL-4 and IL-10
