Antibody Structure Problem Set

Problem 6. Antibody specificity

Replacing the antigen's glutamine 121 with histidine greatly decreases the affinity of the antibody for lysozyme. The best explanation for the difference in affinities is that histidine can't fit into the depression occupied by glutamine. An important implication of this observation:

A. minor changes in antigen structure can dramatically change immune recognition
B. pathogens that mutate frequently are more difficult for the immune system to eliminate

A and B are true

Histidine cannot fit into the antibody’s depression, and binding affinity is greatly reduced. Since a single amino acid change can dramatically effect binding, viruses that make frequent errors in replication can better avoid an immune response. HIV, the virus that causes AIDS, is an important example of this principle.

The Biology Project
The University of Arizona
Tuesday, June 20, 2000
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