IMMUNOSERO // STEVENS CHAP 5: ANTIBODY STRUCTURE AND FUNCTION Flashcards
Glycoproteins found in serum portion of blood
Immunoglobulins
All immunoglobulins are composed of
86% to 98% Polypeptide
2% to 14% Carbohydrate
Serum is placed on an _______ to separate out the proteins
agarose gel and an electrical current
slowest moving proteins
Immunoglobulins
Immunoglobulins appear in ______ band
gamma (γ) band
Considered to be the main humoral element of the adaptive immune response.
Immunoglobulins
Play an essential role in antigen recognition and in Biological activities related to the immune response such as opsonization and complement activation.
Immunoglobulins
Immunoglobulins is Divided into 5 major classes on the basis of heavy chain
- IgG - heavy chain γ
- IgM - heavy chain μ
- IgA - heavy chain α
- IgD - heavy chain δ
- IgE - heavy chain ε
All immunoglobulin molecules are made up of a basic
fourchain tetrapeptide unit
All immunoglobulin molecules are made up of a basic fourchain tetrapeptide unit that consists of:
2 large chains - called heavy or H chains
2 smaller chains- called light or L chains
Heavy and light chains are held together by
- Noncovalent forces and
- Disulfide interchain bridges
The basis structure ofimmunoglobulins are discovered by
Gerald Edelman and Rodney Porter
the most abundant of all the antibodies.
IgG
Centered on using analytic ultracentrifuge to separate out Igs on the basis of molecular weight.
EDELMAN’S WORK
intact IgG molecules: had a sedimentation
coefficient of 7 S
indicates the sedimentation rate in an analytical ultracentrifuge.
Svedberg unit [S]
On obtaining a purified preparation of IgG, Edelman used _____ to unfold the molecule
7M urea
Once unfolded, exposed sulfhydryl bonds could bebroken by a reducing agent such as
mercaptoethanol
Molecular weight of approx. 50,000
Designated as the H chain
3.5 S fraction
Molecular weight of 22,000
Designated as the L chain
2.2 S fraction
used to cleave IgG into 3 pieces of about equal size, each having a sedimentation coefficient of 3.5
S and representing a molecular weight of approximately 45,000 to 50,000 d.
Papain
Carboxymethyl Cellulose Ion Exchange Chromatography separated this material into 2 types of fragments:
Fc fragment
Fab fragment
fragment crystallizable
Fc fragment
fragment antigen binding
Fab fragment
Spontaneously crystallized at 4°C; No antigen-binding ability
Fc fragment
for opsonization and complement fixation.
Fc fragment
Now known to represent the carboxy-terminal
Fc fragment
Consists of:
1⁄2 of two H chains that are held together by S–S bonding.
Fc fragment
Have antigen-binding capacity; one antigen-binding site (2 per Ab)
Fab fragment
Consists of:
1 L chain and
1/2 of an H chain held together by disulfide bonding.
Fab fragment
Uses papain
PORTER’S WORK
Used pepsin to obtain additional evidence for the structure of immunoglobulins.
ALFRED NISONOFF
Cleave IgG at the carboxy-terminal side of the interchain disulfide bonds, yielding One single fragment with a mol. weight of 100,000 d and ALL the antigen-binding ability, known as F(ab’)2
Pepsin
An additional fragment called _______ was similar to FC except that it disintegrated into several smaller pieces.
FC’
was bonded to an H chain by means of an S–S bond
L chain
were joined to each other by one or more S–S bonds
H chain
Amino-terminal end
Variable region
Carboxy- terminal end
One or more constant region
Found in urine of patients with multiple myeloma
Bence Jones proteins
L chains that were being secreted by the malignant plasma cells
Bence Jones proteins
The bench jones proteins when heated to 60°C
Precipitate from urine
The bence jones proteins when further heated to 80°C they;
Redissolve
2 MAIN TYPES OF L CHAIN
Kappa (κ) chains
Lambda (λ) chains
60% of L chains
Kappa (κ) chains
Each contained between 200 and 220 amino acids; from position number 111 onward (the amino terminus is position number 1), it was discovered that each type had essentially the same sequence. This region was called the
constant region
Demonstrates presence of domains similar to those in L chains—that is, variable and constant regions.
HEAVY-CHAIN SEQUENCING
Constant regions of the H chain: Unique to each class and give each immunoglobulin type its name
Isotype
A unique amino acid sequence that is common to all Ig of a given class in a given species.
Isotype
Minor variations of these sequences that are present in some individuals but not others
Allotypes
Occur in the four IgG subclasses, in one IgA subclass, and in the κ L chain.
Allotypes
These genetic markers are found in the constant region and are inherited in simple Mendelian fashion.
Allotypes
Some of the best-known examples of allotypes are variations of the γ chain known as
G1m3 and G1m17.
Variable portions of each chain are unique to a specific Ab
Idiotype
The amino-terminal ends of both L and H chains contain these regions, which are essential to the formation of the antigen-binding site.
Idiotype
The a mino-terminal ends of both L and H chains contain these regions, which are essential to the formation of the antigen-binding site.
Idiotype
The segment of H chain located between the CH1 and CH2 regions
HINGE REGION
It has a high content of proline and hydrophobic residues
HINGE REGION
Chains that do not have hinge region
Mu and Epsilon chains
