Prions Flashcards
Examples of prions
-fore
-kuru
-mad cows
-CDJ
who discovered Kuru
Carleton GaJdusek
Who have Kuru and where are they from
Papua, New Guinea and it is the fore people
What is Kuru
-KURU - Disease known since early 1900’s
“Kuru” in Fore language → “Shivering”
-Disease progression:
Uncontrollable muscular twitching
Decreased muscular coordination
(Cerebellar ataxia)
Decreased ability to walk
Use of sticks as crutches
-Dementia
Disease also known as “Laughing Illness”
Progression to muscle atrophy and paralysis
Death
What is interesting about Kuru brains
they have these huge vacuoles
-Vacuolar spongiform degeneration of neurons
“Kuru” plaques
No inflammation
Which virus is CJD similar to
Kuru
CJD
-A rare sporadic disease of the elderly worldwide
-Incidence 1 per 2,000,000 population per year
i.e. expect about 4 cases per year in Quebec
(population 7,500,000
-Also very similar to 2 genetic syndromes:
Gerstmann-Straussler-Scheinker Syndrome (GSS)
Fatal Familial Insomnia (FFI)
-Familial lineages with very high incidence within families of spongiform encephalopathy
Pourcentage of people getting kuru
Incidence approaching 40% in affected villages
50% of male and female children
60% of adult women
3% of adult males
True or false: Kuru was easily isolated
FALSEEE
They tried to inject kuru brains into chimps and they could not get anything
Scrapie
Scrapie:
-contageous disease
caused
- trembling
- ataxia
- weakness
- strange behavior
- ultimately leading to paralysis and death
Histopathology:
- spongiform encephalopathy without inflammation
- kuru plaques and microfibrillar arrays
True or false scrapie is a non contageous disease
False
-flock which has never been exposed will never
develop the disease
-But if an infected sheep were put into an uninfected flock
-Then all animals in the flock would develop the disease
- only after a 2-5 year incubation period!
-So, Gajdusek telegraphed Australia to check on the chimpanzees from his original brain inoculations
-They were all trembling and badly coordinated
-Their brains showed spongiform encephalopathy!
How did scientists made it work to study kuru
a guy at ucsf inoculated scrapie brain tissue in hamsters and they developed symptoms 30-35 days after inoculation
what did scientits find while studying scrapie brains sds page
-Prusiner fractionated infected brain tissue and assayed it for infectivity
-Infectivity was concentrated in membrane associated fractions
-Analyzing these tissue fractions on SDS-PAGE gels
He found that infected sheep brains contained a protein band that was not present in the uninfected sheep brains
-Similar findings were found in all cases of spongiform encephalopathy in Kuru, CJD, scrapie, etc.
True or false: treatments that affect scrapie were tratments that inactivated nucleic acids?
falseeeee it was treatments that inactivate proteins
Chemical denaturants (alkali, phenol, SDS, etc.)
Proteases
Treatments that inactivate nucleic acid
UV light
psoralens
X-irradiation
DNAse
what are prions
an infectuous agen consisting entirely of proteins
at first scientists hated that shit
What is prp
-scrapie prion protein
-To everyone’s surprise, PrP was encoded by a host cell mammalian gene (now called the PrP gene)
-Constitutively expressed as a membrane protein in:
Neurons, lymphocytes, follicular dendritic cells, intestinal epithelium and many other tissues
-Function of the PrP gene is unknown
Proteinase K treatment of:
(1) PrPsc leaves a proteinase-resistant core PrP 27-30 fragment
(2) PrPc is completely digested
Why does PrPsc differs from PrPc
Because of different post-translational modifications:
-they cause radical changes in 3d folding and physical properties
(a) glycosylation at an additional two sites unused in PrPc
(b) removal of the amino-terminal signal peptide sequence
(c) removal of a carboxy-terminal hydrophobic segment
(d) addition of a C-terminal phosphatidylinositol glycolipid
(e) removal of a variable number of
non-signal amino-terminal amino acid residues
Dramatic conformational difference in the PrP forms
-alpha helical content of PrPc 40%,
little or no beta sheet
-alpha helical content of PrPsc 20% alpha helix,
50% beta sheet
The sum of the changes in prpc
-PrPc is a soluble protein
-PrPsc is stubbornly insoluble
-Localizing in aggregates in infected brain making the brain vacuoles
PRUSINER’S STATEMENT OF THE PRION HYPOTHESIS:
A misfolded form of a protein
This form can then catalyze the refolding of other native
molecules into the same distinct “misfolded” conformation
prp happy state
alpha helical
how to get prpsc
-spontaneous conversion: sporadic
-aquired conversion
-germline mutation, spontaneous conversion more likely: inherited
-somatic mutation, spontaneous conversion more likely: sporadic
true or false prions: disease caused by germline mutation 1 may differ from what caused by germline mutation 2
true
what were the 2 models for prpsc
1: would be inherently more stable than PrPc,
but kinetically inaccessible
PrPsc would catalyze the rearrangement of a molecule
of PrPc to the more stable PrPsc conformation
Infection would depend upon the ability of PrPsc to bind to and
catalyze conversion of existing PrPc
2: CJD would result from a slow rate of
spontaneous conversion of PrPc to PrPsc
Familial syndromes would result from mutations
(a) increasing populations of unstable intermediates
or
(b) an increase in rate of spontaneous conversion
of PrPc to PrPsc
How did people get kuru?
-fore people were canibalists
-men would get gppd parts
-women and kids would get bad parts
-when canibalism stopped so did kuru
How did Mad cows disease got to cows
-in the uk in 1980s, the rendering ptocess for processing animal carcasses was changed
-this meant that dead animals infected with scrapie were fed to cows
-As a result scrapie crossed the species barrier into bovine
True or false: kuru plaques look like alzeimers dementia
treu
What are the symptoms opf mad cows
Cattle affected by Mad Cow
Disease experienced nervousness,
aggression, or other changes in
temperament; abnormal posture;
lack of coordination; difficulty in
rising; decreased milk production;
and/or loss of weight despite
continued appetite, followed by
death.
True or false: mad cows disease never crossed human barriers
false it did
under the form of vCJD
Distinct strains of prion can produce
-distinct and reproducible patters of incubation time
-distinct patterns of cns involvement
-distinct glycosylation and protein cleavage of prpsc
vCJD
-vCJD is a disease distinct from sporadic CJD
-vCJD has a distinct pathology, a younger age of onset, and presents with psychiatric symptoms
-It is likely that vCJD is caused by a different prion strain that was less restricted by the species barrier than that of scrapie
True or false: it is very easy for the scrapie prion to cross species barrier to primates
false
True or false: prion transformation in the cow was initially stimulated by the scrapie prion
true
