Biochemistry I Fall Term, 2000

Lecture 11: Immunoglobulin Structure and Function

Assigned reading in Campbell: Chapter 20.5

Take the Review Quiz on Lecture 11 concepts.

Aspects of Immunoglobulin Structure shows Chime images of antibodies and antibody-antigen complexes:

Side-by-side images on one page (1,950K).

One image per page (248K).

Caution: These pages load some very large coordinate files.
I suggest the use of a campus computer for viewing.
Several of the structures will be shown in lecture.

1. Overview of the Immune System

1. Cellular immunity — T cells
2. Humoral (fluid) immunity — B cells

2. B cell development

1. Self tolerance
2. B cell activation
3. Antibody diversity
   • VJC joining of segments in light chains (7500 different light chains)
   • VDJC joining of segments in heavy chains (100,000 different heavy chains)

3. Antibody Structure

1. Quaternary structure (2 Light + 2 Heavy chains)
2. Production of Ab fragments by papain digestion (Fab & Fc)
   A separate page shows a diagram of Human IgG Structure.
3. Immunoglobulin fold
4. CDR (hypervariable) regions
5. Disulfide bonds

4. Antibody-hapten Interactions

1. Generation of anti-hapten antibodies
2. Specific interactions between Ab and DNP

5. Antibody-antigen Interactions

1. Anti-lysozyme antibody
2. Illustration of epitopes

6. Practical Uses of Immunoglobulins:

1. Fluorescence tagging
2. Purification of materials
3. Immunotherapy
4. Novel chemical reactions

7. Blood Groups

The type ABO antigens are glycoproteins (carbohydrate containing proteins) found on cell surfaces, principally red blood cells.

• Type A antigens are found on type A blood cells; therefore type A antibodies are absent.
• Type B antigens are found on type B blood cells; therefore type B antibodies are absent.
• Type AB antigens are found on type AB blood cells; therefore both type A and B antibodies are absent.
• Neither type A nor type B antigens are found on type O blood cells; therefore both A and B antibodies are present.
• Rh factor is an antigen that is unrelated to ABO, but also important clinically.

Consequences:

• Type A blood can be given to either type A or type AB.
• Type B blood can be given to either type B or type AB.
• Type AB blood can be given only to type AB.
• Type O blood can be given to A, B, AB, and O.

(The antibody proteins in blood are diluted sufficiently during transfusion - you need only worry about the antigens on the red blood cells).

Pre-Lecture Question:
Look at the Immunoglobulin G molecule (248K, on one of the Protein Structures pages) and consider these points:

1. In terms of simple 2° structure elements (a-helix, b-strands, and turns), how would you describe the super-secondary structure called an "IgG fold" on that page?
2. How many IgG folds are found in the immunoglobulin G structure?

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