posted 01-16-2002 11:25 PM
I agree Thermit that prions are an "interesting" mystery these days. They sure are a "new finding".
Who would have thought, a protein molecule could be so invincible and infectious?
Prions are proteins which supposedly cause Mad Cow Disease and variants such as Scrapies. The claim that a protein can do the same thing as infectious agents is in conflict with all scientific principles involved. There are better theories. Spiroplasma appears to be the most likely cause of those diseases.
Mad Cow Disease has the appearance of being genetically engineered, since it lost its usual degree of species specificity. In other words, it jumped species from sheep to cattle and from cattle to humans. However, this property may have resulted from speeded up evolution due to recycling of carcasses as livestock feed.
Scrapies is a disease that destroys the brains of sheep but does not normally affect humans. The causative agent was looked for but never found.
In 1957, a variant of Scrapies was found to affect some human cannibals in New Guinea. The persons who ate the brains of their ancestors acquired the disease; others did not. So the disease was apparently promoted by eating brains.
The human form is now called Creutzfeld-Jacob Disease (CJD). The group of related diseases is called Transmissible Spongiform Encephalopathy (TSE). The Mad Cow form is called Bovine Spongiform Encephalopathy (BSE).
A few years ago, cattle in England acquired the BSE variant of the disease. The precipitating factor was assumed to be the feeding of dead livestock back to livestock.
Soon, a few humans started acquiring the disease presumably from eating the meat of diseased cows. At that point, all cattle in England were slaughtered to protect the humans. There was said to be no evidence of it spreading to USA
Therefore, it was incumbent upon the scientists to explain the cause. No virus could be found, but a protein was being produced in large quantity creating plaques in the brains of the victims. So the protein was said to be the cause of the disease; and it was called a prion.
The protein in question is normally located in the cell membrane, presumably to assist transfer of molecules in or out. Such proteins alternate between two configurations. Over-producing that molecule appears to be how the disease progresses. The resulting brain damage alters behavior resulting in drooling, which is probably a method of spreading the disease.
Supposedly, the prion protein flips to the wrong configuration, while its primary structure (which means the sequence of amino acids in the chain) stays the same. But it can only flip when another one which has flipped influences it. So once the flipping gets started, it keeps going; but it can only be started (usually) from a previously flipped protein, which acts like the causative agent of the disease. Strangely, it is supposed to stay in the flipped configuration while it spreads from animal to animal.
Of course, every respectable scientist initially said that the such a theory was absurd. Eventually, the opposition was neutralized, and the absurd became fact. Recently, one of them (Stanley B. Prusiner) got the Nobel Prize for the theory.
In terms of evolution, prions defy all of the principles. Since the prion is a protein which is coded by the DNA of the victim, it means that the disease is supposedly a product of the evolution of the victim.
Evolution does not work that way. It can only progress toward improvements, not self destruction. There are problems along the way, but they are not promoted by the evolution. Therefore, prions require a new concept which says a disease results from the chance characteristics of a protein, while no evolution is involved in the disease elements of the protein's existence. Yet the chance disease has characteristics similar to other diseases including its ability to destroy the victim and the ability to be transmitted through the environment.
Another problem with the prion etiology is that proteins are not that way. They do not have accidental characteristics; and they do not perform complex functions without necessity and some very demanding evolution. Proteins do not change the configurations of proteins by accident. On top of that, the probability of a changed configuration having just the right characteristics to perform any function is zero. And on top of that, if it could perform a function at all, the probability of that function creating itself is zero. All of those chance probabilities add up to zero times zero, while there is no evolution to improve the odds.
There are other theories for the cause of TSEs. It could be a varient of the rabies virus devoid of a protein coat (a viroid), which is stabilized by wrapping around a small protein.
There is good evidence that the cause of TSEs is spiroplasma. It's a variant of mycoplasma. The evidence is summarized on this webpage: