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Prion: the story on HearLore | HearLore
Prion
In 1982, a single word changed the course of biological science forever. Stanley B. Prusiner, a neurologist at the University of California, San Francisco, coined the term prion to describe a protein that could cause disease without containing any genetic material. This was a concept so radical that it challenged the central dogma of molecular biology, which held that information flows from DNA to RNA to protein, but never from protein back to protein. Prusiner's discovery suggested that a misfolded protein could act as an infectious agent, replicating itself by forcing normal proteins to adopt its abnormal shape. The scientific community was initially skeptical, with many researchers dismissing the idea as impossible. It took years of rigorous experimentation and the eventual isolation of the protein to convince the world that a protein alone could be the cause of a fatal, transmissible disease. The term prion, short for proteinaceous infectious particle, was derived from the words protein and infection, highlighting the unique nature of this pathogen. Unlike viruses, bacteria, or fungi, prions lack DNA or RNA, making them invisible to the immune system and resistant to standard sterilization methods. This discovery opened a new chapter in understanding neurodegenerative diseases, revealing that the very building blocks of life could turn against the organism they were meant to serve.
The Shape of Death
The normal form of the prion protein, known as PrPC, is a harmless component found on the membranes of cells in humans and other animals. It consists of 209 amino acids in humans and has a structure dominated by alpha-helices. This protein plays a role in cell-cell adhesion and intracellular signaling, and it binds copper ions with high affinity, which may contribute to its anti-oxidative properties. However, when PrPC misfolds into its infectious form, PrPSc, the consequences are catastrophic. The infectious isoform has a higher proportion of beta-sheet structure, which makes it resistant to proteases, the enzymes that normally break down proteins. This structural change allows PrPSc to accumulate in the brain, forming amyloid plaques that disrupt tissue structure and lead to cell death. The misfolded protein acts as a template, converting normal PrPC molecules into the infectious form, creating a chain reaction that spreads through the nervous system. The process is insidious, with an incubation period that can last for years, during which the disease progresses silently. Once symptoms appear, the disease advances rapidly, leading to brain damage, dementia, and death. The structural stability of prions makes them resistant to denaturation by chemical or physical agents, complicating disposal and containment, and raising concerns about iatrogenic spread through medical instruments. The discovery of PrPSc has provided a framework for understanding how a single protein can cause a fatal disease, challenging the traditional view of infectious agents.
Who coined the term prion and when did this happen?
Stanley B. Prusiner coined the term prion in 1982 to describe a protein that could cause disease without containing any genetic material. He was a neurologist at the University of California, San Francisco, and his discovery challenged the central dogma of molecular biology. Prusiner was awarded the Nobel Prize in Physiology or Medicine in 1997 for this research.
What is the difference between the normal PrPC and infectious PrPSc forms of the prion protein?
The normal form of the prion protein, known as PrPC, consists of 209 amino acids in humans and has a structure dominated by alpha-helices. The infectious isoform, PrPSc, has a higher proportion of beta-sheet structure, which makes it resistant to proteases and allows it to accumulate in the brain. This structural change enables PrPSc to convert normal PrPC molecules into the infectious form, creating a chain reaction that spreads through the nervous system.
When did the first recorded cases of transmissible spongiform encephalopathies occur?
The story of prions began in the 18th and 19th centuries with a disease called scrapie, which affected sheep and goats. This disease is probably the first transmissible spongiform encephalopathy to be recorded and is characterized by a long incubation period. The disease caused affected animals to lie down, bite at their feet and legs, and rub their backs against posts before becoming lame.
How did the 1980s mad cow disease outbreak affect public health regulations?
The outbreak of mad cow disease in the United Kingdom in the 1980s led to a global crisis with thousands of cattle being culled and millions of people affected. The disease was linked to the practice of feeding cattle meat and bone meal, which contained prions from infected animals. This crisis highlighted the need for stricter regulations on animal feed and the importance of monitoring prion diseases in livestock.
What did researchers discover about fungal prions in the early 1990s?
In the early 1990s, Reed Wickner discovered proteins showing prion-type behavior in the yeast Saccharomyces cerevisiae, which were termed yeast prions. These prions do not always cause disease in their hosts and may have a useful role in adapting to diverse environments. Research into fungal prions has provided strong support for the protein-only concept by demonstrating that purified protein can convert the normal form of the protein into a misfolded form in vitro.
Are there any effective treatments for prion diseases as of 2018?
Despite decades of research, there are no effective treatments for prion diseases as of 2018. Clinical trials in humans have not met with success and have been hampered by the rarity of prion diseases. While some drugs can be prescribed to control specific symptoms, no known way exists to extend the life of a patient with prion disease.
The story of prions began in the 18th and 19th centuries with a disease called scrapie, which affected sheep and goats. The disease caused the affected animals to lie down, bite at their feet and legs, rub their backs against posts, fail to thrive, stop feeding, and finally become lame. The disease was also observed to have the long incubation period that is a key characteristic of transmissible spongiform encephalopathies (TSEs). Although the cause of scrapie was not known back then, it is probably the first transmissible spongiform encephalopathy to be recorded. In the 1950s, Carleton Gajdusek began research which eventually showed that kuru, a disease affecting the Fore people of Papua New Guinea, could be transmitted to chimpanzees by what was possibly a new infectious agent. This work eventually earned him the 1976 Nobel Prize. During the 1960s, two London-based researchers, radiation biologist Tikvah Alper and biophysicist John Stanley Griffith, developed the hypothesis that the transmissible spongiform encephalopathies are caused by an infectious agent consisting solely of proteins. Earlier investigations by E.J. Field into scrapie and kuru had found evidence for the transfer of pathologically inert polysaccharides that only become infectious post-transfer, in the new host. Alper and Griffith wanted to account for the discovery that the mysterious infectious agent causing the diseases scrapie and Creutzfeldt, Jakob disease resisted ionizing radiation. Griffith proposed three ways in which a protein could be a pathogen, with the second hypothesis forming the basis of the modern prion theory. This hypothesis suggested that an abnormal form of a cellular protein can convert normal proteins of the same type into its abnormal form, thus leading to replication. Francis Crick recognized the potential significance of the Griffith protein-only hypothesis for scrapie propagation in the second edition of his Central dogma of molecular biology in 1970, noting that it was a potential contradiction to the established flow of information. The discovery of the prion protein in 1982 by Stanley B. Prusiner confirmed this hypothesis, and he was awarded the Nobel Prize in Physiology or Medicine in 1997 for his research into prions.
The Mad Cow Crisis
The 1980s and 1990s saw the emergence of bovine spongiform encephalopathy, commonly known as mad cow disease, which affected cattle and was transmitted to humans through the consumption of infected meat. This disease, known as variant Creutzfeldt, Jakob disease (vCJD) in humans, was thought to be caused by a prion that typically infects cattle. The human prion disease variant Creutzfeldt, Jakob disease is thought to be caused by a prion that typically infects cattle and is transmitted through infected meat. The disease has a long incubation period, and once symptoms appear, it progresses rapidly, leading to brain damage and death. The outbreak of mad cow disease in the United Kingdom in the 1980s led to a global crisis, with thousands of cattle being culled and millions of people affected. The disease was linked to the practice of feeding cattle meat and bone meal, which contained prions from infected animals. The crisis highlighted the need for stricter regulations on animal feed and the importance of monitoring prion diseases in livestock. The discovery of the prion protein in 1982 by Stanley B. Prusiner confirmed the hypothesis that prions could cause disease in humans, and the mad cow crisis brought the issue to the forefront of public health concerns. The disease has a long incubation period, and once symptoms appear, it progresses rapidly, leading to brain damage and death. The outbreak of mad cow disease in the United Kingdom in the 1980s led to a global crisis, with thousands of cattle being culled and millions of people affected. The disease was linked to the practice of feeding cattle meat and bone meal, which contained prions from infected animals. The crisis highlighted the need for stricter regulations on animal feed and the importance of monitoring prion diseases in livestock.
The Fungal Connection
While prions were initially thought to be unique to mammals, research into fungal prions has provided strong support for the protein-only concept. In the early 1990s, Reed Wickner discovered proteins showing prion-type behavior in the yeast Saccharomyces cerevisiae, which were termed yeast prions. These prions do not always cause disease in their hosts, and some fungal prions are not associated with any disease state, but they may have a useful role. Susan Lindquist's group at the Whitehead Institute has argued that some fungal prions are not associated with any disease state, but they may have a useful role, while researchers at the NIH have also provided arguments suggesting that fungal prions could be considered a diseased state. There is evidence that fungal prions have evolved specific functions that are beneficial to the microorganism that enhance their ability to adapt to their diverse environments. Further, within yeasts, prions can act as vectors of epigenetic inheritance, transferring traits to offspring without any genomic change. Research into fungal prions has given strong support to the protein-only concept, since purified protein extracted from cells with a prion state has been demonstrated to convert the normal form of the protein into a misfolded form in vitro, and in the process, preserve the information corresponding to different strains of the prion state. It has also shed some light on prion domains, which are regions in a protein that promote the conversion into a prion. Fungal prions have helped to suggest mechanisms of conversion that may apply to all prions, though fungal prions appear to be distinct from infectious mammalian prions in that they lack a cofactor required for propagation. The characteristic prion domains may vary among species, and research into fungal prions has provided a new perspective on the nature of prions and their role in disease.
The Alzheimer's Link
In 2015, researchers at The University of Texas Health Science Center at Houston found that plants can be a vector for prions. When researchers fed hamsters grass that grew on ground where a deer that died with chronic wasting disease was buried, the hamsters became ill with CWD. The findings suggest that prions can be taken up by plants that are eaten by herbivores, thus completing the cycle. It is thus possible that there is a progressively accumulating number of prions in the environment. This discovery has raised concerns about the environmental persistence of prions and their potential to spread through the food chain. The study also highlighted the need for further research into the mechanisms of prion transmission and the development of effective sterilization methods. The environmental persistence of prions has been a major concern, as they can remain infectious for years in soil and water. The discovery of prions in plants has added a new dimension to the understanding of prion diseases, suggesting that they may be more widespread and difficult to control than previously thought. The study also highlighted the need for further research into the mechanisms of prion transmission and the development of effective sterilization methods. The environmental persistence of prions has been a major concern, as they can remain infectious for years in soil and water. The discovery of prions in plants has added a new dimension to the understanding of prion diseases, suggesting that they may be more widespread and difficult to control than previously thought.
The Unseen Enemy
Despite decades of research, there are no effective treatments for prion diseases as of 2018. Clinical trials in humans have not met with success and have been hampered by the rarity of prion diseases. Many possible treatments work in the test-tube but not in lab animals. One treatment that prolongs the incubation period in lab mice has failed in human patients diagnosed with definite or probable Variant Creutzfeldt, Jakob disease. Another treatment that works in mice was tried in 6 human patients, all of whom died, before it went out of stock. There was no significant increase in lifespan, but autopsy suggests that the drug was safe and reached encouraging concentrations in the brain and cerebrospinal fluid. While there is no known way to extend the life of a patient with prion disease, some drugs can be prescribed to control specific symptoms of the disease and accommodations can be given to improve quality of life. The World Health Organization recommends any of the following three procedures for the sterilization of all heat-resistant surgical instruments to ensure that they are not contaminated with prions. The challenge of treating prion diseases lies in their unique nature, as they lack genetic material and are resistant to standard sterilization methods. The discovery of prions has opened new avenues for research, but the development of effective treatments remains a significant challenge. The lack of effective treatments has led to a focus on prevention and the development of diagnostic tools to detect prion diseases early. The challenge of treating prion diseases lies in their unique nature, as they lack genetic material and are resistant to standard sterilization methods. The discovery of prions has opened new avenues for research, but the development of effective treatments remains a significant challenge. The lack of effective treatments has led to a focus on prevention and the development of diagnostic tools to detect prion diseases early.