Transcript PRIONS THE INFECTIOUS PROTEINS

PRIONS
THE
INFECTIOUS 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
INTRODUCTION
•
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.
Prion Diseases
Human
•
Kuru
Animal
•
Scrapie
•
Fatal Familial Insomnia (FFI)
•
Bovine Spongiform
Encephalopathy (BSE)
•
Creutzfeldt-Jakob disease
(CJD)
•
Chronic Wasting Disease
(CWD)
Classification of prion diseases
• Infectious/Exogenous
– e.g., Kuru, BSE (mad cow disease), Scrapie
– Spread by
• Consumption of infected material.
• Transfusion.
• Sporadic
• Familial/Hereditary
– Due to autosomal dominant mutation of PrP.
Differences between cellular and scrapie proteins
PrPC
PrPSC
Solubility
Soluble
Non soluble
Structure
Alpha-helical
Beta-sheeted
Multimerisation state
Monomeric
Multimeric
Infectivity
Non infectious
Infectious
Susceptibility to Proteinase K
Susceptible
Resistant
Steps in the biosynthesis of PrP
c
Post-translational processing of PrP
S
C
B
S
A
Cellular trafficking and cleavage of PrP
ER
Endosome
Golgi
Mechanism of Internalization of PrP
C
c
Hypothetical model for a PrP receptor
Model for the function of
LRP- LR as the receptor for PrP
BDII (aa 53-93)
BDI
(aa 144-179)
PrP
HSPG
Dependent
binding
domain
Direct binding
domain (aa
161-179)
LRP/LR
GPI
Heparan sulfate chain
(HS)
Proteogl
ycan
moiety
Sulfated domains
HSPG
Cell Culture Systems for Prion Propagation
Sequence of prion protein
• Antioxidative
Functions of Prion protein
PrPC + Cu (Copper)

Antioxidant activity

Resistance to oxidative stress

Prevent neuronal dysfunction
(Brown et al., 2002)
• Other functions
c
Models for the conversion of PrP to PrP
sc
c
Sc
Time taken for Transformation of mutant PrP to a PrP state
Synthesis of
Mutant PrPc
PIPLCresistant
<10 min
Endoplasmic Reticulum
BFA
180C
0.5-1 hr
Detergent
insoluble
Plasma membrane/
Endocytic Pathway
1-6 hr
Proteaseresistant
Effect of conformation of PrP on Pro K
Model of the cellular pathways
Sc
involved in generation of PrP
c
Proposed model of PrP
aggregation and induction of CtmPrP
Pathogenesis
sc
Mechanism of PrP induced apoptosis
What are Calpains?
 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
Role of Caspases
 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
Factors Responsible for Prion Propagation
The AGAAAAGA Palindrome in Prion Generation
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).
Model for chaperone-supervised PrP conversion
E.g. Hsp70, GroEL
Factors that prevent Prion Replication
 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.
Bertsch et al.,2005

Trimethylamine N-oxide (TMAO), can prevent formation of PrPSc.
Bennion, 2004
Gross and Microscopic Changes
Gross changes
Grossly there is Cortical atrophy and
may also be present.
ventricular
dilatation
Microscopic changes
Scrapie
BSE
Kuru
CJD
Other 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).
Diagnosis
1.
2.
3.
4.
5.
6.
Diagnosis can be made by:
Clinical signs and Symptoms.
Detection of Scrapie
Associated fibrils.
Detection of Abnormal Prion
protein (PrPsc) by Western blotting.
Two dimensional Gel Electrophoresis.
Imunodiagnosis of Prion disease.
Bioassay in Mice.
Scrapie Associated
fibrils.
Mechanism of plaque formation
PrPC
PrPSC
PrPC
PrPsc fibrils
Plaque
Conclusion
 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.