Researchers in the United Kingdom have captured the first direct visualization of two DNA strands locking together. Published in the journal Nucleic Acids Research under the title Imaging and mechanism of DNA-DNA recognition mediated by divalent ions,
the finding confirms a twenty-year-old theory about how electrical repulsion is overcome through divalent ions acting as molecular bridges, offering new insights into cancer and biotechnology.
Resolving a Twenty-Year-Old Structural Enigma in DNA Pairing
For more than two decades, the structural basis of DNA-DNA recognition presented a profound contradiction in molecular biology. Because nucleic acids carry a negative electrical charge, identical molecules should theoretically repel one another rather than make close contact. Yet, these interactions are essential for processes including genetic recombination and gene silencing, and they can also play a role in cancer, alongside fundamental cellular operations like chromosomal condensation and genome organization. To solve this mystery, researchers combined powerful atomic force microscopy with advanced computer simulations to observe the exact moment strands align.
The experimental approach verified a hypothesis originally proposed about twenty years ago—specifically in 2001—by Professor Alexey Kornyshev from Imperial College London and his collaborators. Known as the “DNA zipper” model, or electrostatic DNA zipper / helical coherence model, the theory suggested that counterions or salt ions surrounding DNA could produce alternating patterns of electrical charge. Those patterns, according to the model, would help neighboring DNA molecules align with one another much like two interlocking spiral staircases, allowing for electrostatic interlocking between the positively charged grooves of one duplex and the negatively charged backbone of another.
University of Sheffield and University of York Researchers Map the Mechanism
The breakthrough was achieved by a collaborative team of scientists from the University of Sheffield and the University of York (both UK). By scanning DNA samples with high-resolution atomic force microscopy, a technique capable of mapping surfaces at extremely small scales, the investigators constructed detailed topographical maps showing how short pieces of DNA align with extraordinary precision, matching one another groove for groove in the presence of divalent metal ions.
Simultaneous atomistic molecular dynamics simulations tracked individual atoms and ions as they moved around the molecules. These computational models revealed that double-charged metal ions, such as nickel cations (Ni2+) used when solvating DNA fragments, settle into the DNA grooves and effectively behave like two charged arms. Each ion can interact with both duplexes simultaneously at specific coordination sites within the minor groove, forming a microscopic bridge across the space separating them and helping hold the two strands in alignment.
“It was incredible to be able to directly visualize the long-hypothesized mechanism for the first time. The advanced imaging techniques at our disposal are allowing us to uncover these key DNA interactions which have implications in many key cellular processes.”
Dr. Thomas Catley, co-lead author from the School of Chemical Materials and Biological Engineering at the University of Sheffield
Dr. Victor Velasco-Berrelleza from the University of Sheffield, who performed the simulations, noted the complementary nature of the techniques by explaining that microscopy shows us what happens, but the simulations allow us to uncover the molecular mechanism behind it.
Sequence Hotspots and Implications for Cancer and Biotechnology
The investigations yielded another critical discovery: DNA does not pair equally well along every sequence. Certain stretches of DNA created much stronger contacts than others, producing distinct hotspots where two helices were especially likely to line up. Both the imaging and computational data revealed that coordination sites occur at non-random positions, indicating that the pairing mechanism varies depending on sequence and according to the specific divalent ion. The DNA pairs interacted with each other in almost all simulations containing Ni2+, even if they were not homologous.
Professor Agnes Noy, from the School of Physics, Engineering and Technology at the University of York, who co-led the research, pointed out that identifying these regions carries direct relevance for human health.
“This discovery could help researchers identify regions of the genome specially involved in DNA pairing. These regions may become particularly important when mutations disrupt normal cellular processes and contribute to cancer.”
Professor Agnes Noy, University of York
Beyond oncology and fundamental cell biology, the findings point toward new engineering capabilities. Because some DNA sequences can be programmed to interact more strongly than others, scientists may eventually be able to take advantage of these properties to build customized DNA structures for biotechnology, such as DNA origami, and shed light on how DNA is actually packaged inside cells.
