Sunburn understood

A single electron could be the key to future drugs that repair sunburn say researchers who have witnessed the mechanism by which an enzyme repairs sun-damaged DNA.

Sunburn is caused by UV light, which excites atoms in DNA causing photo-lesions. These legions can become dimers – rings of cyclobutane pyrimidine – which jut out from the side of the DNA, and prevent DNA from replicating properly.

Researchers from Ohio State University have been trying to piece together how the enzyme photolyase can repair damaged DNA for the last decade. Using a laser with a kind of strobe effect to take super-fast measurements, they have – for the first time – witnessed the process in the laboratory.

Photolyase – a naturally occurring enzyme produced in plants and some animals, but not mammals – tears open the misshapen, damaged area of DNA in two places and pieces it back together in its original, undamaged shape

But it doesn’t do this in both places at once – it absorbs visible light, and shoots an electron into the ring to break it up. The electron is shot through the DNA molecule in a circuitous route from one breakup site to the other.

“The enzyme needs to inject an electron into damaged DNA – but how?” said research leader, Dongping Zhong. “There are two pathways. One is a direct jump from the enzyme across the ring from one side to the other. But instead the electron takes the scenic route – there is another molecule that acts as a bridge to speed up the electron flow, and in the way, the long route actually takes less time.”

The researchers hope others can use this knowledge to create synthetic photolyase drugs or even lotions that can repair DNA. Meanwhile, they will be focussing on photoreceptors – the proteins that absorb light and initiate signalling for many biological functions.

The findings were published in the PNAS: http://www.pnas.org/