BMS3021 Lecture Notes - Lecture 14: Heat Shock Protein, Antibody, Hsp70
30 May 2018
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Week 6. Polyglutamine proteins and diseases and
Alzheier’s disease
POLYGLUTAMINE PROTEINS AND DISEASES
• Polyglutamine proteins and disease:
o Defined as string of glutamines in a row (more than 7 = Polyglutamine string)
o Some function just fine
o Expansion of polyQ tract >37Q = neurodegenerative disease
- >35 is the tipping point – tendency to aggregate
-caused by addition of extra CAG codon in gene -> auses loopig ad polyerase a’t
handle
-not well understood but becomes inherited if occurs in germ cells
o Formation of nuclear inclusions (NI) in neurons -> neural dysfunction
o Leads to neuronal dysfunction and death
o Onset is generally 30-50 years (has a lag time)
o Severity and age of disease onset is related to polyQ length:
When the polyQ tract is longer, the age of onset is earlier and disease is more
severe
Youngest is at 7-8 yo –only a year of life left
When CAG is 35-40 onset is ~50yo
o In 9 specific cases, proteins have a higher predisposition to form amyloids
o Eg. Hutigto’s disease = Hutigto
o Eg. Spinocerebellar ataxias (loss of motor control) = Ataxin 1, 2, 3, 6, 7
• Hutigto’s disease:
o Progressive motor impairment, cognitive decline and emotional deterioration
(symptoms of neuronal dysfunction)
o 10% of cases exhibit symptoms <20 (early onset) whereas most are >50
o Alost always present within a family
o Transmitted by both males and females
o Due to unstable CAG repeat in the first exon
o Normal Huntingtin protein has no known function but present in many cells
o Pathology:
Dramatic cell loss in brain due to loss of neuronal cells
Brain weight reduced by 30%
Intranuclear inclusions of Huntingtin and ubiquitin in neurons of striatum and
cerebral cortex – see aggregates and accumulation of ubiquitin (clogged up and
garbage disposal malfunction)
PolyQ aggregates inhibit ubiquitin proteasome system (blocked degradation of
ubiquitin) -> get a clogged up ubiquitin system and cells are not disposed of
find more resources at oneclass.com
find more resources at oneclass.com
• Mechanism of PolyQ toxicity:
o Expanded polyQ disrupts gene transcription
o Tends to draw in nontoxic proteins with glutamine chains – taking away proteins from
their normal functions
o Misfolded polyQ region can bind to proteins such as transcriptional coactivators such as
CBP
o Blockage of proteasome
o Protein aggregates are ubiquitinated
o Leads to build up of many proteins including those involved in regulating cell cycle or cell
survival
o Concentration is associated with lag time i.e. lower concentration = longer lag time
o CAG repeat fibrillisation is protein concentration dependent and Polyglutamine length
dependent
lowest Polyglutamine length even with high concentration = no tendency to
aggregate
Polyglutamine length >37 = concentration dependent formation of aggregates
o Length also affects kinetics
i.e. proteis ith short trats do’t ted to aggregate for a hile hereas >37 has a
greater tendency to aggregate
o Polyglutamine length is proportional to the ability of proteins to aggregate
• PolyQ proteins aggregate via a nucleation dependent mechanism
• PolyQ aggregates are highly toxic in the cell (not specifically nucleus)
• Expanded PolyQ does NOT cause a structural change within proteins
o CD spectrum (secondary structure composition) for ataxin showed no difference
between 27Q and 64Q
o No detectable overall change in structure
• PolyQ and protein stability:
o The longer the PolyQ region the less stable the protein
-equilibrium is being shifted towards the unfolded species
-tendency to form aggregates
o Can test by adding denature factor and see which ones are still folded
- more glutamine = less denaturant needed to destabilise
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Polyglutamine proteins and diseases: polyglutamine proteins and disease, defined as string of glutamines in a row (more than 7 = polyglutamine string, some function just fine, expansion of polyq tract >37q = neurodegenerative disease. >35 is the tipping point tendency to aggregate. Caused by addition of extra cag codon in gene -> (cid:272)auses loopi(cid:374)g a(cid:374)d poly(cid:373)erase (cid:272)a(cid:374)"t handle. When the polyq tract is longer, the age of onset is earlier and disease is more severe. Youngest is at 7-8 yo only a year of life left. When cag is 35-40 onset is ~50yo. In 9 specific cases, proteins have a higher predisposition to form amyloids: eg. Dramatic cell loss in brain due to loss of neuronal cells. Intranuclear inclusions of huntingtin and ubiquitin in neurons of striatum and cerebral cortex see aggregates and accumulation of ubiquitin (clogged up and garbage disposal malfunction) Equilibrium is being shifted towards the unfolded species.
