Anti-ssDNA monoclonal antibody, clone G8-37

Within eukaryotic organisms DNA maintains a double helix structure through two deoxyribonucleotide chains that form hydrogen bonds according to complementary base pairing which creates a stable B-form double helix. The double-stranded DNA structure unwinds temporarily into single-stranded DNA during replication, transcription and DNA repair processes. During cellular processes such as replication and transcription single-stranded DNA forms non-B-form structures like R-loops and G-quadruplexes along with H-DNA and hairpin formations. Numerous critical cellular processes depend on the regulatory activities of ssDNA regions and non-B-form structures with single-stranded segments.

ssDNA can arise during normal biological processes. During replication as well as transcription and repair processes ssDNA forms when dsDNA locally unwinds and some specific sequences transition into non-B-form structures for stable ssDNA regions. These single-stranded DNA structures interact with vital cellular functions through mutual influence and affect transcriptional regulation, DNA replication, homologous recombination repair and meiosis. The single-stranded DNA structure shows higher vulnerability to mutations than double-stranded DNA which requires enhanced protective measures for these regions to maintain genetic stability. Single-stranded DNA-binding protein complexes quickly coat ssDNA once it forms. This coating not only safeguards ssDNA from degradation by nucleases but also coordinates DNA damage checkpoint responses and repair activation.

Figure 1. SSBs bind to ssDNA by wrapping the single DNA strand around the tetrameric protein core
(Source: George NP, et al. 2009)

ssDNA is associated with numerous human diseases. The majority of SLE patients together with mixed connective tissue disease and drug-induced lupus patients generate anti-ssDNA antibodies that target the purine/pyrimidine bases of ssDNA. The exposure of ssDNA regions during apoptosis triggers the immune system to recognize these regions as "non-self" antigens which activates B-cells and initiates antibody production. Hydrogen bonds and π-π stacking together with electrostatic interactions enable anti-ssDNA antibodies to connect with ssDNA. Research shows that both aromatic residues like tyrosine and polar residues located within the antibody's complementarity-determining regions (CDRs) play a key role in producing binding energy. For example, the F33Y mutation can abolish antibody binding by weakening van der Waals forces. Anti-ssDNA antibodies lack specificity for SLE but high levels can help diagnose the disease especially when anti-dsDNA antibodies give negative results. Researchers detect antibodies through ELISA along with IIF and CLIA.

Anti-single-stranded DNA monoclonal antibody