How human IgGs against DNA recognize oligonucleotides and DNA

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Limited understanding of anti-DNA antibody-DNA molecular recognition mechanisms.
• Anti-DNA antibodies are implicated in autoimmune diseases like multiple sclerosis.
• Previous studies lacked detailed data on nucleotide contributions to antibody affinity.

Purpose of the Study:

• To elucidate the molecular mechanisms of DNA recognition by anti-DNA antibodies.
• To determine the relative contributions of nucleotide units to IgG affinity for DNA.
• To compare DNA binding affinities of heavy and light antibody chains.

Main Methods:

• Utilized anti-DNA immunoglobulin G (IgG) from multiple sclerosis patient sera.
• Employed a stepwise increase in ligand complexity approach with single- and double-stranded oligonucleotides.
• Measured binding affinities (Kd) using various DNA and RNA oligonucleotide lengths and structures.
• Constructed thermodynamic models to describe IgG-DNA interactions.

Main Results:

• The DNA-binding site on the heavy chain exhibits significantly higher affinity for deoxynucleotide monophosphates (dNMPs) than the light chain site.
• Both heavy and light chains interact with 2-4 nucleotides, with affinity plateauing at 8-9 nucleotides.
• Ribooligonucleotides show 6- to 100-fold lower affinity compared to deoxynucleotides.
• Heavy chains show moderate affinity increase from single- to double-stranded DNA, while light chains show no change.
• Long supercoiled DNA exhibits approximately 10-fold higher affinity for both chains compared to short oligonucleotides.

Conclusions:

• The heavy chain is the primary driver of high-affinity DNA binding in these anti-DNA IgGs.
• Antibody affinity is dependent on oligonucleotide length, structure (ssDNA vs. dsDNA), and conformation.
• Thermodynamic models provide a framework for understanding the complex interactions between antibody chains and DNA.