Protein Homeostasis and Aging Flashcards
Entire set of proteins expressed by a genome, cell, tissue, or organism under defined conditions
proteome
a state of dynamic equilibrium where protein synthesis and folding are balanced with protein degradation
protestasis
experimented with urea and found that all information required for protein folding is
provided by the amino acid sequence
Anfinsen’s experiment
levinthal paradox
demonstrates that a purely random search for the correct conformation can’t work
folding intermediates
accelerate folding
a chaperone
a protein that interacts with, and aids in,
the folding or assembly of another protein without being part of its final structure
most chaperones are
hsps, their synthesis is induced by stress
how do chaperones work
Many chaperones act by binding exposed hydrophobic regions to prevent nonnative
interactions and protein misfolding
atp dependent
Ubiquitous class of chaperones; constitutively
expressed and stress-induced members
Hsp70s
hsp70 open state
atp bound
hsp70 closed state
adp bound
hsp40 co-chaperones with __ to do ___
with hsp70 to deliver misfolded substrates
hsp90s
Regulation of protein complex assembly and
translocation
which hsp is highly expressed in all species
hsp90s
which hsp stabilizes a number of proteins required for tumor growth, investigated as anti-cancer drugs
hsp90s
whose activity is coordinated by stress inducible phosphoprotein 1 (STl1)
hsp70 and hsp90
which hsp is involved in disaggregation
hsp100s
disaggregase yeast
hsp104
mammalian disaggregase
HSP110 +HSP40 +HSP70
which hsps are involved in prevention of aggregation
hsp 60s and shsps
how do smallHSPs work
surround other proteins to control and sequester aggregates
act early
chaperone functions
Folding/refolding of de novo and
misfolded proteins
Regulate protein complex formation
Mediate the response to proteotoxic
stress (heat shock, oxidative stress,
heavy metals, etc.)
heat shock response
Cellular response to proteotoxic stressors
aimed at restoring protein homeostasis.
results in increased expression of chaperones
HSF-1 is a…
transcription factor
hsf-1 process
triggered by an increase in unfolded proteins
chaperones are titrated away proteins
Hsf1 homo-trimerizes and translocates to the
nucleus to promote transcriptional activity of
HSR gene
secreted or proteins with hydrophobic domains can be properly folded and targeted here
without aggregating.
ER
ultimate goal of the UPRER response
decrease the concentration of misfolded proteins in the ER.
what is UPRer response
a signaling pathway which relieves stress by
selective gene upregulation and other mechanisms
triggered by increase of unfolded proteins
programmed ER stress leads to
apoptosis
oligomerizes, autophosphorylates and
activates its RNase domain to remove an intron from XPB-1 mRNA to facilitate its translation. XPB-1 then binds to specific promoters to activate transcription of UPR genes
IRE1
phosphorylates eIF2α to block the
formation of ribosomal pre-initiation complex and to attenuate translation, while at the same time preferentially translate the ATF4 transcription factor
PERK
migrates to the Golgi upon UPR induction,
where it is cleaved; it moves out to the nucleus and activates transcription from ER-stress responsive promoters.
ATF6
mitochondria has its own
UPR
Within a single cell, the mitochondria can signal to change
nuclear transcription
RNAi disruption of a mitochondrial ETC gene, cco-1 can induce
UPR mito
In C. elegans it is possible to knock down
genes in specific tissues
Strategy: express a hairpin (HP) ds RNA; inverted repeat of a sequence can self anneal into a double stranded RNA
Cell non-autonomous =
inactivate gene in one cell but see the effect in another
Proteo-stress in the mitochondria of one cell (neuron) can be communicated to
induce protein-folding defense in another cell (intestine)
Ubiquitin proteasome system (UPS)
Degrades unnecessary or damaged proteins
through proteolytic activity of proteasomes
Autophagy
Degrades unnecessary or dysfunctional
cellular components through the actions of
lysosomes (organelles, proteins, etc.)
Ubiquitin itself contains 7 lysine residues to
which another ubiquitin can be ligated, forming —
polyubiquitin chains
recognizes Lys-linked chains of 4 or more
ubiquitins
proteasome
Ubiquitin activating enzyme
E1
Ubiquitin conjugating enzymes
E2
Ubiquitin ligases
E3
Ubiquitin process
Ubiquitin gets ligated to a substrate for degradation (more than once)
Polyubiquitin directs to the proteasome, which deubiquitinates it, unfolds it, and degrades it
hollow and provides a cavity with proteolytic
activity
Proteasome 20S core particle
recognize ubiquitinated proteins and regulate
transfer to the catalytic core.
Proteasome 19S regulatory caps
20s core α subunits
interact with the 19S caps and form a gate that blocks unregulated access to the core
20s core b subunits
have the protease activity
19S regulatory particle
binds atp
ATP hydrolysis provides energy for substrate
unfolding (required for transfer into narrow
core)
Removes ubiquitin chain from substrate
Opens gate provided by α subunit
in core
Ubiquitin proteasome system
Degrades unnecessary or damaged
proteins through proteolytic activity of
proteasomes
Autophagy
Degrades unnecessary or dysfunctional
cellular components through the actions
of lysosomes
Lysosomes are
acidic
Macroautophagy
Removes damaged organelles, aggregated
proteins, lipids, and more
* Double membrane structure
fuses
Microautophagy
- Direct engulfment of cytoplasmic material
by lysosomes (organelles, proteins) - Lysosomal membrane invaginates and
engulfs the cytoplasmic material directly
Chaperone-mediated autophagy
(CMA)
Lysosomal degradation of individual proteins
* Selective autophagy pathway
– Hsc70 recognizes KFERQ-like motif
Chaperone and Hsf1 over-expression
improves lifespan
