Exposure to ultraviolet (UV) irradiation can often be harmful to DNA, causing damage and mutations. Researchers have just uncovered the mechanism by which DNA protects itself from UV light, preventing harmful changes in the genetic code.
According to research conducted at Kiel University in Germany, in collaboration with The University of Bristol in the UK, cells funnel the energy from UV light into an innocuous reaction which protects DNA from damage. The results of the study were published in the journal, Angewandte Chemie (Applied Chemistry).
DNA consists of four nitrogenous bases: cytosine, guanine, adenine and thymine. The researchers used a tool called femtosecond spectroscopy – a technique where extremely short blasts of light are directed at the guanine-cytosine base pairs – to determine the effect of UV light on the DNA.
The researchers used that particularly fast method of spectroscopy to monitor the molecular changes, because the DNA’s reaction to UV light occurred within a few quadrillionths of a second. The researchers discovered that a mechanism called electron-driven proton transfer process (EDPT), was triggered when the DNA was irradiated.
The EDPT process begins with displacement of a hydrogen atom within the structure of the DNA. The hydrogen atom is quickly returned to the base however, and the DNA structure returns to normal.
According to Professor Friedrich Temps, head of the Kiel research team from the Institute of Physical Chemistry, “Nature uses the reaction to strengthen the DNA’s resistance to light by orders of magnitude – it is sort of a sun protection for DNA. The DNA building blocks themselves thereby relieve the cells’ hugely complex and very slowly active repair mechanisms using enzymes.”
“The discovery of these enzymes this year was awarded the Nobel Prize for Chemistry,” added Professor Andrew Orr-Ewing, head of the research team in Bristol. Without the passive processes we observed, the cells’ active repair mechanisms would be completely overloaded.”
Though rare, sometimes the EDPT process induced displacement of two hydrogen atoms, preventing the base pair from returning to its original state. “The product could be a mutagen precursor and lead to DNA damage,” said Dr. Katharina Röttger from the University of Bristol, who received her doctoral degree from Kiel University.
“We can only say that the potentially mutagen molecule survived our measurement time frame of one nanosecond – which equals a billionth of a second,” said Röttger. The group says more research is necessary in order to uncover the fate of the radical hydrogen species.
The researchers say the next step is to determine whether the same protective processes occur in longer DNA strands. Due to the more complex nature of long-strand DNA – including interactions with histones and other structural organizations – studying its protective processes could be more complicated.
Sources:
- DNA sun protection – http://www.sciencedaily.com/releases/2015/10/151016084856.htm
- Röttger, K., Marroux, H., Grubb, M., Coulter, P., Böhnke, H., Henderson, A., Galan, C., Temps, F., Orr-Ewing, A., and Roberts, G. (2015). Ultraviolet Absorption Induces Hydrogen-Atom Transfer in G⋅C Watson–Crick DNA Base Pairs in Solution.Angewandte Chemie.
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