How a Key Enzyme Repairs Sun-Damaged DNA

BraveHeart writes "Researchers have long known that mammals, including humans, lack a key enzyme — one possessed by most of the animal kingdom and even plants — that reverses severe sun damage. For the first time, researchers have witnessed how this enzyme works at the atomic level to repair sun-damaged DNA. 'Normal sunscreen lotions convert UV light to heat, or reflect it away from our skin. A sunscreen containing photolyase could potentially heal some of the damage from UV rays that get through.'"

Comments

Other DNA damage?

[kombipom]

Any reason why this couldn't be used to repair damage from other forms of radiation or carcinogens?

Re:Other DNA damage?

[MachDelta]

IANAB but as far as I understand it photolyase only repairs a certain type of damage found between adjacent cytosine and thymine (or uracil) units. That just happens to be the type of damage most commonly caused by UV radiation, so the enzyme can be understood as a fix for that particular method of damage. Other forms of radiation or chemical carcinogens effect DNA in a variety of other ways, most of which photolyase won't have an affinity for, rendering it ineffective.

As a car analogy... photolyase is like caranuba wax. It'll fix the small scratches and minor dings, but if some jackass comes along and smashes your windows and kicks in your doors you won't have much luck trying to buff it out. :)

Re:Other DNA damage?

[MachDelta]

Er, I meant affect.

Damnit. Now I have to go sit in the corner. :(

It is not that straightforward

[Anonymous Coward]

Well, if it was present with all plants and animals (except mammals) why did evolution lose such a "useful" enzyme? Or more importantly, what functionality did the body get while losing it? Without understanding these basic questions, it would be foolhardy to get such a product and start using it all over our body.

Re:It is not that straightforward

[BlackGriffen]

Things can disappear due to genetic drift. If the tail of mammals living underground or nocturnal for a long time is true, for instance, then losing the gene to repair sun damage wouldn't be a big deal. Considering that color vision is rare in mammals, another thing only useful in broad daylight, it wouldn't surprise me if it was just lost randomly. I mean, do you really think it's useless to have 3 color vision? Or 4, as is common in many other animal kingdoms? Add in the fact that so many mammals are covered in enough fur/hair that they don't have that much sun exposure and a loss by genetic drift is a virtual shoe-in.

Same thing with human's inability to produce our own vitamin C.

Re:It is not that straightforward

[Thanshin]

Well, if it was present with all plants and animals (except mammals) why did evolution lose such a "useful" enzyme?

I've always imagined the evolutionary criteria as "The absolute minimum required to maximize chances of reproduction" and not "Everything that might be useful".

Otherwise we'd have poisonous fangs, wings, the ability to digest cellulose and, possibly, firebreath not dependant on a mexican diet.

Re:It is not that straightforward

[GospelHead821]

Cancer is a disease that affects organisms late in life. Generally speaking, they will have already had an opportunity to reproduce by the time that they develop cancer. The introduction of this mutation could have been completely coincidental and it would not have affected the reproductive fitness of the organisms that had it. You might suggest that damage to DNA has consequences besides cancer but it actually doesn't, really. If a cell's DNA becomes too corrupt but the cell doesn't become cancerous as a result, just that one cell is likely to die. You're constantly making new skin cells anyway.

Interpretation of TFA

[kurokame]

IMO the summary is a bit vague on certain points. This sort of gives the impression that the enzyme is restoring "lost data" which was corrupted by exposure to UV, which would amount to dark sorcery.

To get a bit more specific, what seems to be happening from TFA is that the UV dumps some unexpected energy into the DNA (things like light frequency, energy level, time distribution, and so forth probably play a part). This causes the DNA to fold up in order to store the received energy, and it binds to itself in a way it's not supposed to. When transcription or whatever occurs, the normal processes do their thing but aren't aware that the UV light has secretly substituted their normal DNA storage for something which is connected to itself in ways it shouldn't be. The enzyme acts as a catalyst to break these "bad" bonds, which are presumably characteristically different than the "good" bonds which make up the DNA molecule's structure, and probably weaker as well. Therefore the enzyme can break up the "bad" bonds so that the normal cellular processes get what they expect without the enzyme itself posing a risk to the DNA.

Short and simple version: the UV light makes the DNA get tangled up in ways it shouldn't like a user playing with cables, and the enzyme untangles this mess so that the cellular processes can actually find which cord goes where.

Ohio University Press Release is Misleading

[CuteSteveJobs]

> Researchers have long known that mammals, including humans, lack a key enzyme -- one possessed by most of the animal kingdom and even plants -- that reverses severe sun damage

The story description is misleading. By careful omission it gives the impression that this enzyme is the only one that can repair sun-damaged DNA damaged by UV, emphasizing that humans lack it. OH CRUEL LORD! But we do in fact already have other enzymes that repair DNA damage and these are very old news. Ohio U. are just talking about one mechanism, but the press release makes it sound like the only one.

http://en.wikipedia.org/wiki/DNA_repair
http://www.ncbi.nlm.nih.gov/pubmed/8053698

Seems to be a trend with journal articles: Release the journal article and a popular press article; Take huge liberties with the popular press article to guarantee widespread media coverage (and we guess future funding and sunscreen merchandising). Note Ohio U. is the source of the journal article and this press release:
http://www.medicaldaily.com/news/20100725/550/researchers-discover-how-key-enzyme-repairs-sun-damaged-dna.htm

We saw the same thing recently with the silly "chicken or egg" article:
http://www.guardian.co.uk/science/2010/jul/18/chicken-and-egg-conundrum-solved

I'm not knocking either journal article. What they did was pretty cool, but would these people please learn to be honest in their press releases too? You would think they would have learned from Climategate?

Re:the real hazard of sunscreen

[priegog]

Oh no. Not this armchair doctor thing again.
* Vitamin D is NOT "the anti-cancer vitamin" It's a molecule that serves as a hormone to regulate calcium metabolism. It also happens to seem to help prevent some types of cancer, due to semi-related processes. But AFAIK, it has only DEMONSTRATED to reduce the incidence of colon cancer. For skin cancer, it has only been suggested.
* In developed nations, most of us get way more vitamin D from enriched foods and such than we need. So there is no need to go jumping through hoops to get it. Specially hoops that involve you being exposed to a PROVEN carcinogenic (the sun). And even if you somehow DON'T want to believe we get enough vitamin D as-is, remember that to get your daily dose of vitamin D, you only need to expose your forearms (or the equivalent amount of skin) to th sun for 10 minutes. So trust me, even if you wear tons of sunblock, and spend your day under an umbrella, you WILL be getting more than enough vitamin D that way. Heck, you'll get it in the driving up to the beach before you even see the sea.
* Melanoma (the most deadly form of skin cancer, and definitely right up there amongst the deadliest forms of cancer) is associated with repeated ACUTE sunburns (specially in childhood and early adulthood). Basaliomas and epitheliomas are amongst the most common forms of ANY cancer, and are not very deadly. In fact, when found, they often only need to be removed to treat them. These kinds of cancer are (proven, and causally at that) associated with CHRONIC sun exposure. Every little bit of sun counts for this one, as it has a cumulative effect.
* Because of all of this, I think it is pretty stupid to recommend NOT to use sunblock (which would effectively be turning an acute sunburn into a minor exposure), specially when the reason is so that "you can synthetize more of the anti-cancer vitamin". It is also stupid to suggest that everything can be fixed by "taking a vitamin C dose after a sunburn". Where on earth did you get that from? What studies is this claim based on?

This is not to say, things wouldn't be better if people actually used sunblock correctly, or if instead of going to the beach you simply stayed in your mom's basement. But alas, IRL sometimes you need to go the beach to have a little social life. And when you do, you should wear sunblock. Even if you do so incorrectly, some is better than nothing, and even SUGGESTING you should forgo it completely in favor of taking some random pills hoping to cancel out cell damage is stupid, naive, and just irresponsible. I do agree that wearing hats, and long sleeves > sunscreen, but they are not mutually exclusive, you know... and then again, as I said, sometimes you go to the beach to have a good (semi-naked) fun time, not to go hide under a rock.

So please just keep your pseudoscience and personal choices to yourself. Or at least don't recommend people do the same. It's just stupid.