Proteins and Prions
What are proteins?
Proteins [pro-teens] are essential to life and are found in all living things. Proteins are contained in every part of your body: skin, muscles, hair, blood, body organs, eyes, fingernails, and bones. Next to water, protein is the most plentiful substance in your body.
Protein is primarily used to build, maintain and repair body tissues, but there are thousands of different proteins that carry out a variety of jobs in your body. The structure of a protein determines its function.
Loose strings of amino acid are the "building blocks" of proteins. These strings then fold and curl into complex three-dimensional shapes that allow the protein to do its job. Two common shapes are an alpha helix (looks like a spiral staircase) and a beta sheet (a flattened out shape).
What are prions?
In 1982, Dr. Stanley B. Prusiner of the University of California, San Francisco purified an infectious agent uniquely made of protein and named it "prion" [pree-on], short for "proteinaceous infectious" particle. Dr. Prusiner was awarded the Nobel Prize in Physiology or Medicine in 1997 for his discovery that Creutzfeldt-Jakob disease (CJD) was caused by prions.
The normal prion protein is found throughout the body and brain. While not essential to life, it does seem to play a role in helping your neurons communicate and transport minerals. Its amino acid chains fold into a mainly helical shape.
How do prions cause CJD?
In Creutzfeldt-Jakob disease and other prion diseases, the prion protein folds into an abnormal shape where the flat sheet structure replaces the helix, which means the protein can't do its normal job.
Unlike any other known protein, abnormal prion proteins are infectious. This was a radical discovery because proteins don't contain the genetic material that allows viruses and bacteria to reproduce.
These misfolded proteins induce other prions to misfold. Then these misfolded prions build up in the brain and cause the infected brain cells to die. When the infected cells die, prions are released into normal tissue and go on to infect more cells without any reaction from the immune system. Eventually, large clusters of cells die leading to the mental and behavioral symptoms of prion diseases.
Prion diseases are the only known diseases that can be sporadic, genetic or infectious.
What other prion diseases exist?
The following diseases are believed to be caused by prions.
- Scrapie in sheep and goats
- Bovine spongiform encephalopathy (BSE) in cattle ("mad cow disease")
- Transmissible mink encephalopathy (TME) in mink
- Chronic wasting disease (CWD) in North American cervids (mule deer, white-tailed deer, elk and moose)
- Feline spongiform encephalopathy in cats
- Exotic ungulate encephalopathy (EUE) in nyala, oryx and greater kudu
- Sporadic forms:
- Sporadic Creutzfeldt-Jakob disease (sCJD)
- Sporadic Fatal Insomnia (sFI)
- Genetic forms:
- Familial Creutzfeldt-Jakob disease (fCJD)
- Gerstmann-Sträussler-Scheinker syndrome (GSS)
- Fatal Familial Insomnia (FFI)
- Acquired forms:
- Iatrogenic Creutzfeldt-Jakob disease (iCJD)
- Variant Creutzfeldt-Jakob disease (vCJD)