Scientists have disproved the prevailing theory of how DNA binds itself in the signatory double helix, finding it is not the hydrogen bonds which hold together the two sides of the hereditary material as previously thought.
Instead, the researchers at Chalmers University of Technology in Sweden, found that water is the key to the double helix. The discovery, published in the journal PNAS, opens doors for new understanding in research in medicine and life sciences.
DNA is constructed of two strands, consisting of sugar molecules and phosphate groups. Between these two strands are nitrogen bases, the compounds which make up organisms genes, with hydrogen bonds between them. Until now, it was commonly thought that those hydrogen bonds were what held the two strands together.
However now, the researchers show that the secret to DNA’s helical structure may be that the molecules have a hydrophobic or water repelling interior, in an environment consisting mainly of water. The environment is therefore hydrophilic or water attracting, while the DNA molecules nitrogen bases are hydrophobic, pushing away the surrounding water.
When hydrophobic units are in a hydrophilic environment, they group together, to minimise their exposure to the water, the researchers said.
The role of the hydrogen bonds, which were previously seen as crucial to holding DNA helixes together, appears to be more to do with sorting the base pairs, so that they link together in the correct sequence, they said. The discovery is crucial for understanding DNAs relationship with its environment, according to the researchers.
“Cells want to protect their DNA, and not expose it to hydrophobic environments, which can sometimes contain harmful molecules,” said Bobo Feng, one of the researchers behind the study. “But at the same time, the cells DNA needs to open up in order to be used,” Feng said. “We believe that the cell keeps its DNA in a water solution most of the time, but as soon as a cell wants to do something with its DNA, like read, copy or repair it, it exposes the DNA to a hydrophobic environment,” said Feng.
Reproduction, for example, involves the base pairs dissolving from one another and opening up. Enzymes then copy both sides of the helix to create new DNA. When it comes to repairing DNA, the damaged areas are subjected to a hydrophobic environment, to be replaced, researchers found.
A catalytic protein creates the hydrophobic environment. This type of protein is central to all DNA repairs, meaning it could be the key to fighting many serious sicknesses, they said. Understanding these proteins could yield many new insights into how we could, for example, fight resistant bacteria, or potentially even cure cancer, the researchers noted.
Bacteria use a protein called RecA to repair their DNA, and the researchers believe their results could provide new insight into how this process works — potentially offering methods for stopping it and thereby killing the bacteria.
In human cells, the protein Rad51 repairs DNA and fixes mutated DNA sequences, which otherwise could lead to cancer. “To understand cancer, we need to understand how DNA repairs. To understand that, we first need to understand DNA itself,” said Feng. “So far, we have not, because we believed that hydrogen bonds were what held it together. Now, we have shown that instead it is the hydrophobic forces which lie behind it. We have also shown that DNA behaves totally differently in a hydrophobic environment,” Feng said.
“This could help us to understand DNA, and how it repairs. Nobody has previously placed DNA in a hydrophobic environment like this and studied how it behaves, so its not surprising that nobody has discovered this until now,” said Feng.