PRIONS PRIONS
THE THE
INFECTIOUS PROTEINSINFECTIOUS PROTEINS
Paras Yadav*, Jaspreet Singh Arora*, Sachinandan De*, Tirtha Kumar Datta*, Surender Lal Goswami*, Aarti Bhardwaj$, Shalini Jain# and Hariom Yadav#
*Animal Biotechnology, #Animal Biochemistry Division, National Dairy Research Institute, Karnal-132001, Haryana, India
$Meerut Institute of Engeenering and Technology, Meerut, U.P., India
• Stanley B. Prusiner coined the term proin from Proteinaceous infective particle
and changed to prion to sound it rhythmic.
• Prion diseases were caused by misfolded proteins.
• Elucidated the gene and mechanism by which wild type protein bring about the
clinical disease.
INTRODUCTION
• Kuru
• Fatal Familial Insomnia (FFI)
• Creutzfeldt-Jakob disease (CJD)
• Scrapie
• Bovine Spongiform Encephalopathy (BSE)
• Chronic Wasting Disease (CWD)
Prion DiseasesPrion Diseases
HumanHuman AnimalAnimal
Classification of prion diseasesClassification of prion diseases• Infectious/ExogenousInfectious/Exogenous
– e.g., Kuru, BSE (mad cow disease), Scrapie– Spread by
• Consumption of infected material.• Transfusion.
• SporadicSporadic
• Familial/HereditaryFamilial/Hereditary– Due to autosomal dominant mutation of PrP.
Differences between cellular and scrapie proteinsDifferences between cellular and scrapie proteinsPrPPrPCC PrPPrPSCSC
SolubilitySoluble Non soluble
Structure Alpha-helical Beta-sheeted
Multimerisation state Monomeric Multimeric
InfectivityNon infectious Infectious
Susceptibility to Proteinase KSusceptible Resistant
Steps in the biosynthesis of PrPSteps in the biosynthesis of PrPcc
Post-translational processing of PrPPost-translational processing of PrP
S S
AC B
ER Golgi
Endosome
Cellular trafficking and cleavage of PrPCellular trafficking and cleavage of PrP
Mechanism of Internalization of PrPMechanism of Internalization of PrPCC
Hypothetical model for a PrPHypothetical model for a PrPc c receptorreceptor
Model for the function ofModel for the function of
LRP- LR as the receptor for PrPLRP- LR as the receptor for PrP
HSPG
Dependent binding domain
Direct binding domain (aa 161-179)
LRP/LR
PrP
BDI
(aa 144-179)
Heparan sulfate chain (HS)
Sulfated domains
HSPG
Proteoglycan moiety
GPI
BDII (aa 53-93)
Cell Culture Systems for Prion PropagationCell Culture Systems for Prion Propagation
Sequence of prion proteinSequence of prion protein
PrPC + Cu (Copper)
Antioxidant activity
Resistance to oxidative stress
Prevent neuronal dysfunction
(Brown et al., 2002)
• AntioxidativeAntioxidativeFunctions of Prion proteinFunctions of Prion protein
• Other functionsOther functions
Models for the conversion of PrPc to PrPsc
Time taken for Transformation of mutant PrPTime taken for Transformation of mutant PrPc c to a PrPto a PrPScSc state state
Detergentinsoluble
PIPLC-resistant
Synthesis of Mutant PrPc
Protease-resistant
<10 min
BFA
180C
0.5-1 hr
1-6 hr
Endoplasmic Reticulum
Plasma membrane/
Endocytic Pathway
Effect of conformation of PrP on Pro KEffect of conformation of PrP on Pro K
Model of the cellular pathways Model of the cellular pathways involved in generation of PrPinvolved in generation of PrPScSc
Proposed model of PrPProposed model of PrPcc
aggregation and induction of CtmPrPaggregation and induction of CtmPrP
PathogenesisPathogenesis
Mechanism of PrPMechanism of PrPscsc induced apoptosis induced apoptosis
They generate a C-terminal fragment(C2) which has molecular
weight of 27-30 kDs.
Increase in intracellular levels of Calcium increase
production of terminal fragments .
Calpastatin prevents production of C2.
Inhibitors of lysosomal proteases has no effect on C2
production.
Telling et al.,2004
What are Calpains?What are Calpains?
It was proposed that prion-associated toxicity involves altered
trafficking of PrPc.
Inhibition of ubiquitin-proteasome system(UPS).
Deposition of aggresomes of PrPSc in nerve cells.
Induction of Apoptosis with activation of Caspase 3 and
Caspase 8.
Complete molecular basis for neuronal death is not known.
Aggregates of over expressed PrPc does not cause cell death.
Tabrizi et al., 2005
Role of CaspasesRole of Caspases
The AGAAAAGA Palindrome in Prion Generation
Factors Responsible for Prion PropagationFactors Responsible for Prion Propagation
Norstrom & Mastrianni, 2005
Factors Responsible for Prion Propagation cont…
• PrPc association with lipid rafts in the early secretory pathway.
• Creutzfeldt–Jakob disease (CJD) in Libyan Jews, linked to the E200K mutation in PRNP (E200KCJD).
E.g. Hsp70, GroEL
Model for chaperone-supervised PrP conversionModel for chaperone-supervised PrP conversion
Phospholipase A2 Inhibitors prevent prion replication.
Platelet-activating Factor Antagonists also inhibits prion replication.
Bate et al.,2004
Drugs which share a N-benzylidene-benzohydrazide core structure.
Trimethylamine N-oxide (TMAO), can prevent formation of PrPSc.
Factors that prevent Prion ReplicationFactors that prevent Prion Replication
Bertsch et al.,2005
Bennion, 2004
Gross and Microscopic Changes Gross and Microscopic Changes
Grossly there is Cortical atrophy and Grossly there is Cortical atrophy and ventricular ventricular dilatation dilatation
may also be present.may also be present.
Gross changes
ScrapieScrapie BSEBSE
CJDCJDKuruKuru
Microscopic changes
• Gliosis within plaques.
• Loss of oligodendrocytes within plaques.
• Axons usually remain intact in plaques.
• Both CD4+ and CD8+ lymphocytes are present in active
lesions.
(Kretzschmar et al.,1996, Wilesmith et al.,
1997).
Other microscopic changesOther microscopic changes
Diagnosis can be made by:
1. Clinical signs and Symptoms.
2. Detection of Scrapie
Associated fibrils.
3. Detection of Abnormal Prion protein (PrPsc) by Western blotting.
4. Two dimensional Gel Electrophoresis. 5. Imunodiagnosis of Prion disease.
6. Bioassay in Mice.
Diagnosis Diagnosis
Scrapie Associated fibrils.
PrPC
PrPSC
PrPC
Mechanism of plaque formationMechanism of plaque formation
PrPsc fibrils
Plaque
Molecular hallmark of the disorder is the accumulation of abnormal prion protein(PrPSc).
Physiological functions of cellular prion protein (PrPc) is not clear.
Identity of intracellular compartment where PrPc to PrPSc occurs is not established.
Prion peptide of 106-126 residues is found to be neurotoxic.
Studies on prion protein will open the avenues for treatment of other neurodegenerative disorders.
ConclusionConclusion