Somatic hypermutation maintains antibody thermodynamic stability during affinity maturation

Area of Science:

• Immunology
• Structural Biology
• Protein Engineering

Background:

• B cells undergo somatic hypermutation and clonal selection to produce high-affinity antibodies.
• Antibody maturation is traditionally viewed as enhancing antigen specificity and binding energy.

Purpose of the Study:

• To investigate the role of somatic mutations in antibody thermodynamic stability.
• To understand how mutations affect both antigen binding and protein structure.

Main Methods:

• Analysis of antibody crystal structures (93F3 and OKT3).
• Comparison of germ-line and mutated antibody variants.
• Assessment of melting temperature to determine thermodynamic stability.

Main Results:

• Somatic mutations directly impacting antigen binding can reduce antibody stability (e.g., 93F3 antibody).
• Distal somatic mutations can compensate for reduced stability, enhancing overall protein integrity.
• Mutations in antibody OKT3 simultaneously increased affinity and thermodynamic stability.
• Structural analysis revealed mutations at the variable heavy and light chain interface modulate stability.

Conclusions:

• Antibody maturation optimizes not only antigen affinity but also protein thermodynamic stability.
• Peripheral somatic mutations are crucial for counteracting destabilizing effects of affinity-enhancing mutations.
• Antibody evolution parallels enzyme evolution, optimizing function and stability concurrently.