The Stealthy Assassin
Prions are infectious particles that propagate by inducing existing proteins (PrPc) to convert into a misfolded form (PrPsc). This newly converted protein continues the chain reaction by guiding even more unsuspecting proteins into the prion form.3 Prions are highly resistant to degradation against proteases, such as ubiquitin because their secondary structure transforms from an alpha helix to a beta sheet. This results in a buildup of amyloids. Amyloids are protein aggregates consisting of tightly packed beta sheets that form fibrils and tangles in the brain. Alzheimer's, another amyloid-forming disease, causes dementia that worsens over time.
“Recombinant proteins such as the prion protein shown here are often used to model how proteins misfold and sometimes polymerize in neurodegenerative disorders.”6
Like other pathogens, prions spread from one organism to another. The highest concentrations of prions exist in the brain, spinal cord, and digestive tract, but they can also be found in virtually any tissue, including blood.7 The most common mode of transmission is ingestion, but humans have also been infected through blood transfusions and surgery with contaminated tools. Since prions are infectious, they possess an extreme resistance towards sterilizing measures. In general, they are resistant to heat, ionizing radiation, proteases, and traditional autoclave treatments. To make matters worse, some variants of prions in mice are able to cause infection via air.5
Prions tend to take on a sinister side once they infect the body. Edward Hoover of Colorado State University describes prions: “[they] are like the enemy within, the alien in some B-movie that transforms people to an evil version. The
Structure of amyloid-forming prion protein
Image from: NIH (Douglas Fowler, University of Washington) CC SA