Photo: Enzymlogic,
Licence: CC-BY-SA 2.0
(October 16, 2015) UV radiation often damages our DNA. Researchers at Kiel
University and The University of Bristol, Great Britain, have now seen for the
first time what happens in DNA building blocks when they are stimulated by
ultraviolet light, and what they do to prevent themselves from being destroyed.
The results show: the molecules use the absorbed energy to set off a completely
harmless reaction which prevents the genes being altered. The study can be
found in the current edition of the journal Angewandte Chemie (Applied
Chemistry).
Our DNA contains the bases adenine, guanine, cytosine and
thymine. The chemists used ultra short blasts of light to shoot base pairs
guanine and cytosine which were stimulated with UV light. They were only able
to reveal the protective molecular mechanism using this method of femtosecond
spectroscopy, because the process happened within a few quadrillionths of a
second.
During the so-called electron-driven proton transfer process
(EDPT), a hydrogen atom is displaced within the molecular compound. The base
pair, however, immediately returns to its original starting structure from the
same procedure. "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", said Professor Friedrich Temps, head of the Kiel research team from
the Institute of Physical Chemistry. "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. Without the passive processes we observed, the
cells' active repair mechanisms would be completely overloaded", added
Professor Andrew Orr-Ewing, head of the team in Bristol.
In a few cases, however, the base pair was not able to
return to the original situation. Here, EDPT caused two hydrogen atoms to be
displaced. "The product could be a mutagen precursor and lead to DNA
damage", explained Dr Katharina Röttger from the English working group,
who received her doctoral degree in Kiel. Future experiments will have to show
what then happens to this molecule. "We can only say that the potentially
mutagen molecule survived our measurement time frame of one nanosecond (= a
billionth of a second)", said Röttger.