Antibody Structure - Weeblyjohnjhaddad.weebly.com/uploads/2/5/2/0/2520519/lecture-11.pdf ·...
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Antibody Structure
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Carbohydrate forces CH2 domains to bulge; this impacts the Fc regions ability perform effector functions.
Carbohydrate addition is important for structure & function.
Antibody Antigen Interactions
Epitopes may be composed of AA that are linear or conformational:
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Vp1 protein:- white= epitopes exposed to the immune system.
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AA in Ag are located adjacent to one another in the primary seq.
Protein Folding:May Not be essential
Ab will bind todenatured Ag.synthetic peptide.
Sequential / Linear epitope:
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Conformational / Nonsequential epitope / Discontinuous:
Primary AA seq of Ag:
Ab will not bind to:Denatured AgShort synthetic peptide
Protein Folding Required:
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Protein antigens can contain both sequential & conformational epitopes:
HEL- 8 epitopes with most being nonsequential.
Sperm whale myoglobin: - 5 Sequential epitopes (shown in
blue) - several nonsequential (not
shown)
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Experiment:Prepared synthetic peptides of the HEL loop:
Open or closed.Competition Studies:
Immunology (kuby), Fig. 3-8
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Sequential epitopes may require tertiary structure & disulfide bonding in the Ag:
Antibody Antigen Interactions
A closer look at the antigen-antibody molecular interaction
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Comparison of Ab interactions with small protein Ag to that of large globular proteins:
Kuby, fig 3-4
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The size & conformation/shape of Ag impacts the Ab surface contacts:
Small protein Ag HIV peptide HEL
Ab CDR
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Fig. 3-5, kuby: Influenza virus antigen
VL
VH
11/5/2009 16Antibody binding is Reversible.
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Larger globular antigens often attract by
electrostatic interactions & H bonding:
HEL: Glutamine on HEL is the critical interaction:
Salt bridge
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Affinity versus AvidityAffinity: Strength of one Ab binding site bound to a single antigenic epitope.
Strength of noncovalent interactions.
Low affinity Ab-binds Ag weaklyDissociates more quickly.
High affinity Ab-binds Ag tightlyRemains bound longer.
http://www.bio.davidson.edu/misc/movies/antibody.mov
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Avidity- Strength of multiple interactions between a multivalent Ab & multivalent Ag.
The affinity of 1 Ab binding site to 1 epitope does not reflect the true strength of an Ab-Ag interaction.
High avidity can compensate for a low affinity.
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Cross reactivitySpecificity- Ab recognizes one epitope.
Example: anti-Hemagglutinin (Measles virus) Ab.
S. PneumoniaeCapsule Ag-A-1
S. PyogenesCapsule Ag-A-2
Cross reactivity-Anti-S. pneumoniae capsular Ab
- Binds S. pneumoniae epitope A-1 - Binds also to S. pyogenes A-2 with lower aff
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