PRIONS-structure, multiplication, diseases.pptx

PRIONS are infectious agents composed primarily of sialoglycoprotein.
This protein is called prion protein (PrP)
They contain no nucleic acid.
They cause a variety of neurodegenerative diseases in humans and animals.
According to STANLEY PRUSINER,
Prions- ‘which means proteinaceous and infectious (-on by analogy to virion) that lacks nucleic acid’.
It refers to a previously undescribed form of infection due to protein misfolding . While the infectious agent was named prion, and the specific protein that make the prion was named PrP i.e. ‘protease resistant protein’.
PRIONS proteins in the form of fibres which also occur as fold rods.
The normal protein found in a variety of tissues is referred to as PrPC (C refers to cellular or common PrP), whereas the misfolded form of PrPC is called PrPSc which is responsible for the formation of amyloid plaques that results in neurodegeneration.
PrPSc is the infectious form of PrPC, (Sc refers to scrapie, a prion disease occurring in sheep) .
PrPc is a Alpha helical while PrPSc is a beta pleated sheet
PrPc do not contain beta sheet.
PrPc protein can adopt 2 distinct different stable conformations.
All known prions induce the formation of an amyloid fold in which the protein polymerizes into an aggregate consisting of tightly packed beta sheets.
This altered structure is extremely stable and accumulates in the infected tissue causing cell death and tissue damage resulting in death of animals.
It is supposed that the diseased form of PRION (PrPSc) originated spontaneously or transmitted through ingestion of food/feed directly interacts with the normal endogenous form PrPC and enables to rearrange its structure.
As a result of interaction the normal form PrPC is converted to abnormal form (PrPSc) .
It is assumed that an unidentified cellular protein (protein X) helps the conversion of PrPC to PrPSc by bringing a molecule of each of the two together into a complex.
Main reason for the cause of prions is ‘cannibalism’ i.e. eating of one human by another human.
2 types of cannibalism – endocannibalism (eating humans from the same community) and exocannibalism ( eating humans from other communities).
The tribal ground up the brain into a pale grey soup, heated it and ate it.
Therefore, ingestion of brain tissue of dead relatives for religious reasons was likely the route of transmission.
In cattles
-BOVINE SPONGIFORM ENCEPHALOPATHY
(mad cow disease).
2. In humans
-ALZHEIMER’S DISEASE
DOWN’S SYNDROME
FATAL FAMILIAL INSOMNIA
KURU LEPROSY

1. PRIONS STRUCTURE AND MULTIPLICATION Presenter- RASHMI M G 1 ST YEAR Msc. Botany MAHARANI’S SCIENCE COLLEGE FOR WOMEN MYSORE

2. INTRODUCTION Microorganisms make a significant contribution and are therefore, studied for their importance to human life. They have also helped in the development of biotechnology. Microorganisms affect both positively and negatively on human life. The theory of spontaneous generation states that the microbes arise automatically in decomposing organic matter.

3. PRIONS An infectious agent different from both viruses and viroids can cause disease in animals and humans. This agent is called prions (proteinaceous infectious particles).

4. History of prion s In 1957, during the visit to NEW GUINEA, Carleton Gajdusek was informed by a local physician about half of deaths of the tribals in the remote places due to the mysterious disease. Later on this disease was named as KURU i.e. shaking/ shivering by the local inhabitants. Mostly women and children exhibit involuntary tremors at the early stage of disease. Thereafter, the patients pass through stages of increased debilitation and dementia leading to death. This disease spreads due to a kind of ritual cannibalism involving the eating of parts of brains of the deceased as a mark of homage to the later. The patients dying of KURU did not show any of symptoms of infection of CNS. No virus toxin or chemical abnormalities could be isolated in the laboratories of AUSTRALIA.

5. History of prions STANLEY B. PRUSINER is an AMERICAN neurologist and biochemist. He discovered prions which are a class of infectious self-reproducing pathogens mainly composed of protein. He won Nobel Prize in Physiology or Medicine in 1997 for his work proposing an explanation for the cause of bovine spongiform encephalopathy (mad cow disease) and its human equivalent, Crutzfeldt- Jacob disease.

6. PRIONS According to STANLEY PRUSINER, Prions- ‘which means pr oteinaceous and in fectious (-on by analogy to viri on ) that lacks nucleic acid’ . It refers to a previously undescribed form of infection due to protein misfolding . W hile the infectious agent was named prion, and the specific protein that make the prion was named PrP i.e. ‘protease resistant protein’.

7. PRIONS PRIONS proteins in the form of fibres which also occur as fold rods. The normal protein found in a variety of tissues is referred to as PrP C (C refers to cellular or common PrP), whereas the misfolded form of PrP C is called PrP Sc which is responsible for the formation of amyloid plaques that results in neurode generation. PrP Sc is the infectious form of PrP C , (Sc refers to scrapie, a prion disease occurring in sheep) .

8. PRIONS- structure PrP c is a Alpha helical while PrP Sc is a beta pleated sheet PrP c d o not contain beta sheet. PrP c protein can adopt 2 distinct different stable conformations.

9. Can A PRION or PROTEIN be infectious? All known prions induce the formation of an amyloid fold in which the protein polymerizes into an aggregate consisting of tightly packed beta sheets. This altered structure is extremely stable and accumulates in the infected tissue causing cell death and tissue damage resulting in death of animals.

10. CONFORMATIONAL CHANGE

11. PRION REPLICATION It is supposed that the diseased form of PRION (PrP Sc ) originated spontaneously or transmitted through ingestion of food/feed directly interacts with the normal endogenous form PrP C and enables to rearrange its structure. As a result of interaction the normal form PrP C is converted to abnormal form ( PrP Sc ) . It is assumed that an unidentified cellular protein (protein X) helps the conversion of PrP C to PrP Sc by bringing a molecule of each of the two together into a complex .

12. CAUSES OF PRION DISEASES Main reason for the cause of prions is ‘cannibalism’ i.e. eating of one human by another human. 2 types of cannibalism – endocannibalism (eating humans from the same community) and exocannibalism ( eating humans from other communities). The tribal ground up the brain into a pale grey soup, heated it and ate it. Therefore, ingestion of brain tissue of dead relatives for religious reasons was likely the route of transmission.

13. DISEASE CAUSED BY PRIONS In cattles - BOVINE SPONGIFORM ENCEPHALOPATHY (mad cow disease). 2. In humans - ALZHEIMER’S DISEASE DOWN’S SYNDROME FATAL FAMILIAL INSOMNIA KURU LEPROSY

14. COMPARISON VIRUS VIROIDS PRIONS GENOME DNA/ RNA RNA NONE STRAND Ds / ss ss Ss COAT Capsid and envelope For HDV only None TARGET Animals, plants, bacteria, archaea Plants animals HOST CELL/ ORGAN All types of cells Plants cell Nervous system

15. CONCLUSION PRIONS re infectious agents composed primarily of sialoglycoprotein. This protein is called prion protein (PrP) They contain no nucleic acid. They cause a variety of neurodegenerative diseases in humans and animals.

16. REFERENCE A Textbook of Microbiology By D.K.Maheshwari PAGE No. 416-420 A Textbook of Microbiology Dubey R.C. & Maheshwari D.K. S. Chand Publishing, 2023