Unraveling DNA self-protection

Protect yourself againt the sun. This benign sentence repeated sumer after summer is far from being futile. UV light is known to affect DNA. After different mecanisms it can lead to irreversible leasions and thus skin cancer. But DNA can also defned itself ! Researchers from the  laboratoire de physique et de chimie théorique (Université de Lorraine/CNRS) and the university of Valencia (Spain) helped by our lab unraveled a defense mecanism unprecedented. The double helix is able to interact with surrounding sodium atoms to trigger chemical reactions acting as countermeasures against UV light.

This new mecanism was found when studying proton transfer between four DNA base pairs (A/T and G/C). These transfers are triggered by UV-light, lead to mutations by creating defects subsequently replicated. For 3 months, 50 cores computed the dynamics of hundreds of atoms. It was then possible to scrutinize the trajectory computed at a high level of precision. Researchers oberved two types of transfers :

• one already known ;
• and a new one, much shorter (1 ps) involving a double back and forth proton transfer. The first step creates an unstable basic intermediate which immediately transfers back the protons to their initial base.

As the double transfer is lightening fast, it prevents a long term transformation of DNA and thus the propagation of the lesion. As this novel mecanism is favored by nearby sodium ions (Na+), it means that the local charge plays a crucial to stabilize DNA as an unviolable gene bank. The study in regions where the charge is highly positive such as histones is thus of considerable interest.