How human IgGs against DNA recognize oligonucleotides and DNA

In the literature, there are no available data on how anti-DNA antibodies recognize DNA. In the present work, to study the molecular mechanism of DNA recognition by antibodies, we have used anti-DNA IgGs from blood sera of patients with multiple sclerosis. A stepwise increase in ligand complexity approach was used to estimate the relative contributions of virtually every nucleotide unit of different single- (ss) and double-stranded (ds) oligonucleotides to their affinity for IgG fraction having high affinity to DNA-cellulose. DNA-binding site disposed on the heavy chain demonstrates higher affinity to different dNMPs (K_d  = 0.63μM-3.8μM) than the site located on the light chain (28μM-170μM). The heavy and light chains interact independently forming relatively strong contacts with 2 to 4 nucleotides of short homo- and hetero-d(pN)_2-9 . Then the increase in the affinity of different d(pN)_n became minimal, and at n ≥ 8 to 9, all dependencies reached plateaus: approximately 3.2nM to 20nM and approximately 200nM to 460nM for the heavy and light chains, respectively. A similar situation was observed for different ribooligonucleotides, in which their affinity is 6-fold to 100-fold lower than that for d(pN)_n . Transition from ss to ds d(pN)_n leads to a moderate increase in affinity of ligands to DNA-binding site of heavy chains, while light chains demonstrate the same affinity for ss and ds d(pN)_n . Long supercoiled DNA interacts with both heavy and light chains with affinity of approximately 10-fold higher than that for short oligonucleotides. The thermodynamic models were constructed to describe the interactions of IgGs light and heavy chains with DNA.