Are not prions particular proteins that have folded incorrectly? Do they not cause other proteins of the same chemical structure, folded correctly, to fold into the new state? http://www-micro.msb.le.ac.uk/3035/prions.html
Anyone who’s read “Cat’s Cradle” by Kurt Vonnegut will remember a particularly horrifying concept called ice-nine. The premise is that multiple crystal shapes of water exist, with different melting points each. The end of the book comes with a crystal of ice-nine, with a melting temperature of one hundred fouteen degrees Fahrenheight (uncertain - 121 F? 117? something like that), touching the ocean. Any land-bound piece of water would have done, for as soon as that seed of ice-nine touched liquid water, the water froze into ice-nine and continued all the way around the globe.
Are not prions the same? I mean, it’s a much slower and easier-to-counteract process, but won’t the Earth eventually be overwhelmbed? Or am I just being silly, because protein is inherently easier to destroy than water, separating into its component atoms, which can be used normally again… arg.
Prions don’t just float about in the air, infecting anything they touch. They have to be introduced to the body, via eating or injection or some such mechanism. I don’t know how the Earth itself might be overwhelmed, but if all of humanity practiced cannibalism, and ate Kuru-infected brains, I suppose humanity’d all be infected eventually. That’s a pretty unlikely situation, I think. Most prion diseases are quite rare.
And I think the chain reaction is some fictious license. My (limited) opinion is that prions are an infection which could possibly spread out of control - look at the diseases in your link. It’s possible.
Don’t put it in the frame of Earth, though. Earth has nothing to fear from prions.
Righto, GilaB, but I was thinking more along the lines of a slower transmission - like simple things like the food chain and also through transmission along microorganisms. Mayhap also through simple shedding along an organism’s path. lost in sweat and urine and hairs and scales and shit. I had the impression that proteins were fairly stable molecules, and would stay around until broken by heat or enzymes.
Woah! cool site Jake4. Seems to say that the current crystal state of ice is very dependent on pressure and temperature, and that a crystal cannot accrete more water molecules without the proper pressure, and will at best remain static at STP, and probably melt or revert to ice-1. Still leaves the possibility, though.
Nope, beta-amyloid (AB) is not a prion. It’s a hunk of the Amyloid Precursor Protein (APP) that has been cut with Beta Amyloid Cleaving Enzyme (BACE). There are several theories out regarding AB aggregation. However, the pathways have been sufficiently elucidated to know that it’s not a spontaneous self-catalyzing reaction of the nature of Prion protein (PRP or PRNP) aggregation. APP is absolutely vital to neuron development, and AB may have some necessary function as well. The thing is that something goes wrong with the normal clearing mechanism and/or BA piles up faster than it can be cleared. It has been demonstrated that the inflammatory response can increase AB. Likewise, head injury is a risk factor. Lahiri et al has a good review in a recent Journal of Alzheimer’s Disease on the topic. Likewise, eating a lot of cholesterol may be a risk factor. It can induce amyloid plaques in laboratory animals–but only if the animals drink non-distilled water. Right now, we and many other labs are looking into this very recent discovery to see if we can track down a single substance or if it’s a complex combination. It doesn’t look like it’s some sort of industrial pollutant. Aluminum has not been found to cause APP increase or plaque build-up, though. There is a correlation, but no “give them aluminum and plaques appear”. So the aluminum may be a “side effect” of amyloid plaque and not a cause. However, the aluminum work has led to other promising avenues.
Age is probably the strongest documentable risk factor. Likewise, education seems to delay symptoms and correlate with slower progression of alzheimer’s. Oddly enough, there is also a negative correlation between head size and Alzheimer’s progression. The theory is that people with bigger heads may simply have more brain tissue they can “afford” to lose.
Getting back to the original post: There is little chance of prions “taking over”. Prion diseases in the real world are horizontally transmitted by eating a sufficient amount of misfolded PrP. The reason we have seen a recent upswing in humans is that the dimwits in agribusiness thought it was a good idea to inflict cannibalism on livestock. That practice is being curtailed. However, prion diseases have been known for a long time (although the causes were long unknown). As to why it spontaneously occurs, that’s another of those multi-cause issues. Again, there seems to be some correlation between high production of PRNP and the likelihood of spontaneous misfolding. Several pathways are currently being explored. Inflammation may be an issue here, too. And cholesterol might again be a villain.
Take-home message right now: Based on current research, there is no solid rule, but it’s a good idea to keep the cholesterol content of ones diet low–but we already knew that for many other reasons. Active life is also a good idea.
In any case, as scary as these diseases might be, there are many other causes of death that take effect before dementia becomes noticeable. Eat properly, exercise regularly, never stop learning. These things are still your best bet.
In a small minority, one just got a bad roll of dice, but outright direct genetic causes are rare.
“Heat” in such a case can be as low as “room temperature”. “Naked” proteins can be pretty fragile. As for enzymes–they’re all over the %)(#%^)(#&^%(*^@#&^$)%(& place, as anybody whose samples have mysteriously degraded in the laboratory knows. Bacteria and fungi are hungry little things.
In general, it used to be that sick animals were not eaten and it was not normal practice to feed livestock to each other. Recently, it became the practice to slaughter animals as soon as they showed any symptoms. This is now illegal in many countries. Likewise, it is now becoming illegal to inflict cannibalism on livestock.
Some comments on some things said here, including the original question:
Prions can only “infect” similar proteins. When you get a prion disease, copies of a particular protein that you normally produce get “converted” to the misfolded prion form–it doesn’t affect every protein in your body. Therefore, prions couldn’t spread in the way you’re afraid they could spread. A particular prion can only spread to a species that has similar proteins (ie, it probably wouldn’t hurt you to eat a chicken with the chicken prion, because it’s a different protein–don’t test that out without further research, though; I don’t know for certain that the chicken prion is all that different from the mammalian prion
However, prions are stable little bastards. Prions are resistant to heat denaturation, salt denaturation, and even proteolytic enzymes. They are not broken down nearly as fast as they’re formed, as many (but not all) “normal” proteins are broken down.
Sorry, don’t have any cites handy… but my doctoral candidacy paper involved prions, and I came to know way more than I ever wanted to know about them in a few short months (actually, my roommate did something on yeast prions for his candidacy the following year, increasing my prionation still further )
Still leaves the possibility, though.