Prions: definition, examples, meaning, Structure, Topic

What Are Prions?

Prions are small particles that lack all nucleic acid and are made up of only protein, hence referred to as prions. They are not normal versions of a protein found in the brain – prion protein (PrP) but are misfolded versions of PrP. This misfolding sets off the chain reaction where normal PrP changes to the abnormal prion form to cause scalping and severe neurodegenerative diseases.

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This Story also Contains

1. What Are Prions?
2. Characteristics Of Prions
3. Difference between prions and other infectious agents (bacteria, viruses, fungi).
4. Biology Of Prions
5. Mechanism Of Disease Progression: Pathogenesis of Prion diseases
6. Impact on the Nervous System
7. Treatment And Prevention
8. Recommended Video on Viruses, Viroids and Prions

The credit for identifying prions goes to Stanley B. Prusiner, who in the 1980s discovered this new pathogen which he came to be associated with the Nobel Prize in Physiology or Medicine in 1997. Prions are since been an important subject of interest in biology and medicine due to their contribution to fatal diseases like CJD and BSE or mad cow disease. Knowledge about prions is necessary for the creation of diagnostic tests and treatments for these diseases and other similar diseases.

Characteristics Of Prions

The mode of action and the conformation of prions make them highly peculiar and categorically different from all other pathogens.

Structure And Composition

Prions do not have nucleic acids, hence they are not viruses or bacteria but are composed of protein only. The first part is a scrapie prion protein which is an abnormal fold of the cellular prion protein, and conformational isomer.

The specific feature of the misfolded protein is the presence of β-sheets, but not α-helices, as in the case with the normal protein. This structural change is significant because it lets prions alter normal protein into the pathogenic configuration.

Prions are equally very resistant to proteases, these are enzymes that can degrade proteins. This resistance supports their build-up in the environment and dissemination through populations of cells and organisms.

Diagram showing normal and misfolded protein in Prion.

Difference between prions and other infectious agents (bacteria, viruses, fungi).

Biology Of Prions

Transmissible spongiform encephalopathies or TSEs are a group of fatal neurological disorders in which prions play roles as the causative agents. These diseases are caused by a build-up of abnormal prion proteins in the brain, which in turn, causes degeneration of the brain and finally, death.

Prion Diseases (Transmissible Spongiform Encephalopathies - TSEs)

TSEs are transmitted through company consumption and impact people and animals. The features which differentiate this group are long incubation periods, spongiform changes in the damaged part of the brain and no immune response to the prion.

Classification

Prion diseases can be classified based on their origin:

Sporadic:

• Be unpredictable and have no identifiable traits that could be a warning sign that it could happen.

• Creutzfeldt-Jakob disease can be of various subtypes but the most frequent is sporadic Creutzfeld-Jakob disease and it is responsible for 85% of all CJD cases.

Familial:

• From a genetic makeup influencing the prion protein gene (PRNP).

• Educate diseases for example, Familial Creutzfeldt-Jakob Disease (CJD), Gerstmann-Sträussler-Scheinker Syndrome (GSS), and Fatal Familial Insomnia (FFI).

• Make up 10-15% of all prion disease cases.

Acquired:

• Consequence of getting infected by prions from food products, medical procedures, or by any other means.

• Some of these are the variant Creutzfeldt-Jakob Disease which results from BSE-tainted food, Kuru from the West Africans’ tradition of cannibalism, and iatrogenic CJD from surgeries.

• These cases are however limited but very important particularly because they are infectious.

Examples Of Prion Diseases

Some diseases caused by prions are:

Creutzfeldt-Jakob Disease (CJD)

Description: This disease is in the list of human prion diseases that are characterized by progressive and fatal neurodegeneration.

Types:

• Sporadic (sCJD): It is not related to any certain timeline or period.

• Familial (fCJD): Inherited.

• Iatrogenic: by medical interventions.

• Variant (vCJD): Associated with meat products that infected BSE.

Kuru

Description: A tropical neurological disease that was discovered among the fore people of Papua New Guinea.

Transmission: In vain, cut off the arms, leaves in the hands of the dying, the hearts were eaten Aimarams alongside the urine and faeces – throw it into the mud, and the meat is not made.

Symptoms: Shaking, imbalance and components of the neurodegeneration process.

Bovine Spongiform Encephalopathy (BSE or Mad Cow Disease).

Description: Influenced cattle tend to spongy degeneration of the brains.

Transmission: From contaminated feed, the animals take in the feed that has been infected with the bacteria thus causing the disease.

Impact: That can be passed on to humans in the form of vCJD.

Chronic Wasting Disease (CWD)

Description: Impacts deer, elk, and moke species include:

Symptoms: Slimming, transformations in behaviour, and brain degradation.

Transmission: By contact with fluids that come out of our bodies and surfaces that are touched by several people every day.

Mechanism Of Disease Progression: Pathogenesis of Prion diseases

The diseases include Creutzfeldt-Jakob Disease, Gerstmann-Sträussler-Scheinker Syndrome and many others are neurological disorders which are due to the abnormal post-transformation of normal cell surface prion proteins (PrP^C) into abnormal cell surface proteins (PrP^Sc). PrP^Sc is resistant to proteases and preferentially accumulates in an insoluble form, which is the form of insoluble fibrils. These fibrils build up in the brains upsetting the normal running of neurons and causing neurodegeneration.

Impact on the Nervous System

Neuronal Damage: The increase of PrP^Sc results in neuronal degeneration that involves the regions of the brain that control memory, voluntary muscle movements, and balance.

Spongiform Changes: The brain tissue acquires a spongy consistency due to vacuolation due to neuronal cell death and disruption of cell membranes.

Inflammatory Response: Microglia and astrocytes are activated by prions leading to neuroinflammation, but no classic immune response is called for.

Clinical Manifestations

The clinical course of the disease progresses through various stages, each with distinct neurological and psychiatric features.

Symptoms And Signs

Early Symptoms: This may comprise of deficit in memory, confusion, psychiatric disorders such as depression, anxiety, altered sensory experiences or sensations.

Motor Symptoms: Degeneration to ataxia, mere tremors, myoclonic jerks, and subsequent dementia.

Advanced Stages: Alzheimer's dementia, akinetic mutism and terminal stages are coma.

Progression Of Symptoms.

Rapid Onset: Sporadic and variant may be rapidly progressive, hence may lead to death within a few months to a couple of years.

Variable Course: Thus, the onset and the course of pathological changes in familial forms can be different due to the variety of genetic mutations.

End-Stage: Total involvement of the brain and limbs along with the fatal outcome primarily due to the development of complications, such as pneumonia or renal shutdown.

Treatment And Prevention

Methods that can be adapted to prevent the diseases are:

Current Treatment Strategies

Symptomatic Relief: Covers general aspects, signs and so on such as pain and anxiety.

Supportive Care: It offers ‘’Comfort Care’’ to enhance the patient’s quality of life.

Experimental Therapies: Currently there is research that is being done on possible cures in the form of drugs that address themselves to controlling the replication of prion and protein misfolding.

Prevention Strategies

Food Safety: Laws that have been put in place to curb transmission through meat products.

Screening: Screening for blood, and tissues to minimize the iatrogenic transmission hazards.

Decontamination: Finding environments which are appropriate for washing the tools, the accessories and the equipment which are used in the medical field.

Education: A review of prion diseases and their risks to enhance the knowledge level of people.

Recommended Video on Viruses, Viroids and Prions