A single engineered amino acid substitution changes antibody fine specificity

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• Somatic hypermutation introduces genetic variations into antibody V region genes during humoral immunity.
• In vitro studies suggest these mutations often enhance antibody affinity for antigens.
• Antibody specificity is crucial for effective immune responses.

Purpose of the Study:

• To investigate the impact of a specific amino acid mutation on antibody specificity.
• To determine if somatic mutation in vivo can alter antibody binding characteristics.
• To explore the potential of antibody engineering for modifying antigenic specificity.

Main Methods:

• In vitro mutagenesis of an unmutated antibody with specificity for p-azophenylarsonate (Ars).
• Analysis of a somatically mutated anti-Ars antibody (36-71) with known crystal structure.
• Structural examination of antibody-antigen interactions to elucidate specificity changes.

Main Results:

• A single amino acid replacement at position 35 in the heavy chain conferred specificity for p-azophenylsulfonate (Sulf) while abolishing Ars specificity.
• The mutant antibody bound Sulf with high affinity, similar to memory B cells.
• Structural analysis indicated altered binding site size and/or hydrogen bond geometry caused the specificity shift.
• This mutation was observed in somatically mutated antibodies after immunization with Ars followed by Sulf.

Conclusions:

• Somatic mutation in vivo can indeed alter antibody specificity.
• Antibody engineering holds potential for redirecting antibody specificity.
• Understanding mutation-driven specificity changes is key to antibody development.