Process Reveals How Key Enzyme Repairs Sun-Damaged DNA

Researchers long known that humans lack a key enzyme--one possessed by most animals and even plants--that reverses severe sun damage. For the first time, researchers have observed how this enzyme works at the atomic level to repair sun-damaged DNA.

In July 2010, in the early online edition of the journal Nature, Ohio State University (Columbus, USA) physicist and chemist Dr. Dongping Zhong and his colleagues reported how they were able to see the enzyme, called photolyase, inject a single electron and proton into an injured strand of DNA. The two subatomic particles healed the damage in a few billionths of a second. "It sounds simple, but those two atomic particles actually initiated a very complex series of chemical reactions,” said Dr. Zhong, an associate professor of physics, and associate professor in the departments of chemistry and biochemistry at Ohio State. "It all happened very fast, and the timing had to be just right.”

Precisely how photolyases repair the damage has remained a mystery until now. "People have been working on this for years, but now that we've seen it, I don't think anyone could have guessed exactly what was happening,” Dr. Zhong said. He and his colleagues synthesized DNA in the lab and exposed it to ultraviolet light, producing damage similar to that of sunburn, then added photolyase enzymes. Utilizing ultrafast light pulses, they took a series of "snapshots” to reveal how the enzyme repaired the DNA at the atomic level.

Ultraviolet (UV) light damages skin by causing chemical bonds to form in the wrong places along the DNA molecules in our cells. This research has demonstrated that photolyase breaks up those errant bonds in just the right regions to cause the atoms in the DNA to move back into their original positions. The bonds are then arranged in such a manner that the electron and proton are automatically ejected out of the DNA helix and back into the photolyase, presumably so it could start the cycle over again and go on to heal other sites.

All plants and most animals have photolyase to repair severe sun damage. Only mammals lack the enzyme. Humans do possess some enzymes that can undo damage with less efficiency. But people become sunburned when the DNA is too damaged for those enzymes to repair, and our skin cells die.

Now that researchers know the process by which photolyase works, they might use that information to engineer drugs or lotions that heal sun damage, according to Dr. Zhong.

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