The structural basis for DNA binding by an anti-DNA autoantibody

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• Autoantibodies like MAb 2C10 play a role in autoimmune diseases such as lupus.
• Understanding the molecular interactions of autoantibodies with DNA is crucial for developing targeted therapies.

Purpose of the Study:

• To identify critical amino acid residues within the DNA binding site of the anti-double-stranded DNA (anti-dsDNA) autoantibody MAb 2C10.
• To elucidate the roles of specific complementarity-determining regions (CDRs) in antibody-DNA interactions.

Main Methods:

• Site-directed mutagenesis was employed to systematically alter amino acid residues within MAb 2C10.
• Molecular modeling was used to visualize and interpret the structural basis of DNA binding.
• Binding activity was assessed by measuring the antibody's affinity for DNA after mutagenesis.

Main Results:

• Simultaneous mutation of four Arginine residues in CDR3H abolished DNA binding.
• Mutations in CDR1H (Phe32, Asn35) decreased DNA binding, while mutations in CDR1L (Asp residues) increased it.
• Mutation of specific residues in CDR3L (Asp92, Asn93) reduced DNA binding activity, indicating their role in specificity.

Conclusions:

• Multiple amino acids across different CDRs contribute to DNA binding and specificity of MAb 2C10.
• The L-chain, particularly CDR1L, appears to hinder DNA binding, while CDR3 domains of both heavy and light chains contribute to specificity.
• Electrostatic interactions are suggested to play a significant role in the binding of MAb 2C10 to DNA.