1. Announcements • literature search due today! Feb 4! • Worth a 10 pt quiz grade. • Case Studies: • There are three case studies that were provided: Case 10, 11, & 12. Please do case study 10 & 12 only. Case 11 was provided for information that may assist with Case 12.

2. Antibody Structure

4. Carbohydrate addition is important for structure & function. • Carbohydrate forces CH2 domains to bulge; this impacts the Fc regions ability perform effector functions.

5. Antibody Antigen Interactions Epitopes may be composed of AA that are linear or conformational:

6. Vp1 protein: - white= epitopes exposed to the immune system.

7. Sequential / Linear epitope: • AA in Ag are located adjacent to one another in the primary seq. • Protein Folding: • May Not be essential • Ab will bind to • denatured Ag. • synthetic peptide.

8. Conformational / Nonsequential epitope / Discontinuous: • Primary AA seq of Ag: • Protein Folding Required: • Ab will not bind to: • Denatured Ag • Short synthetic peptide

9. HEL- 8 epitopes with most being nonsequential. Sperm whale myoglobin: 5 Sequential epitopes (shown in blue) several nonsequential (not shown) Protein antigens can contain both sequential & conformational epitopes:

10. Experiment: Prepared synthetic peptides of the HEL loop: Open or closed. Competition Studies: Immunology (kuby), Fig. 3-8

11. Sequential epitopes may require tertiary structure & disulfide bonding in the Ag:

12. Antibody Antigen Interactions A closer look at the antigen-antibody molecular interaction

13. Comparison of Ab interactions with small protein Ag to that of large globular proteins: Kuby, fig 3-4

14. The size & conformation/shape of Ag impacts the Ab surface contacts: Ab CDR HEL Small protein Ag HIV peptide

16. VL • Fig. 3-5, kuby: Influenza virus antigen VH

17. Antibody binding is Reversible.

18. Larger globular antigens often attract by electrostatic interactions & H bonding: • HEL: • Glutamine on HEL is the critical interaction: • Salt bridge

19. Affinity: Strength of one Ab binding site bound to a single antigenic epitope. Strength of noncovalent interactions. Low affinity Ab- binds Ag weakly Dissociates more quickly. High affinity Ab- binds Ag tightly Remains bound longer. Affinity versus Avidity http://www.bio.davidson.edu/misc/movies/antibody.mov

20. 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.

22. S. Pyogenes Capsule Ag-A-2 S. Pneumoniae Capsule Ag-A-1 Cross reactivity • Specificity- Ab recognizes one epitope. • Example: anti-Hemagglutinin (Measles virus) Ab. • Cross reactivity- • Anti-S. pneumoniae capsular Ab • - Binds S. pneumoniae epitope A-1 • - Binds also to S. pyogenes A-2 with lower affinity