Prions

Sometimes a scientific discovery shakes the confidence of scientists, making them question whether they truly understand nature's ground rules. That's exactly what prions have done to scientists' understanding of the ground rules for infectiousdiseases. Prions cause diseases,but they aren't viruses or bacteria or fungi or parasites. They are simply proteins, and proteins were never thought to be infectious on their own. Organisms are infectious, proteins are not. Or, at least, they never used to be. Prions entered the public's consciousness during the mad cow epidemic that hitEngland in 1986. For decades, however, scientists had searched for unusual, atypical infectious agents that they suspected caused some puzzling diseases that could not be linked to any of the "regular" infectious organisms. One possibility was that slow viruses-viruses that spent decades wreaking havoc in their hosts-might be the culprits, and these putative viruses were not only leisurely about multiplying but also hard to isolate. Now researchers are coming around, although reluctantly, to accepting the shocking fact that naked proteins can be infectious. Prions enter cells and apparently convert normal proteins found within the cells into prions just like themselves. The normal cell proteins have all the same
"parts" as the prions- specifically the same amino acid building blocks -but they fold differently. They are much like the toy "Transformers" that were around in the 1980s. They could change themselves in to be different shapes with nothing added and nothing subtracted. Prions enter brain cells and there convert the normal cell protein PrPC to the prion form of the protein, called PrPSC. When normal cell proteins transform into prions, amino acids that are folded tightly into alpha helical structures relax into looser beta sheets. More and more PrPC molecules transform into PrPSC molecules, until eventually prions