Protein degradation rate varies 100x

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• Protein degradation rate varies 100x
• Most have motifs marking them for
  polyubiquitination taken to proteosome
  destroyed
• Other signals for selective degradation include
  PEST KFERQ
• PEST found in many rapidly degraded proteins
• Deletion increases t1/2 10x, adding PEST drops
  t1/2 10x
• Sometimes targets poly-Ub
• Recent yeast study doesnt support general role
• KFERQ cytosolic proteins with KFERQ are
  selectively taken up by lysosomes in
  chaperone-mediated autophagy under conditions of
  nutritional or oxidative stress.

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• Protein degradation in bacteria
• Also highly regulated, involves chaperone-like
  proteins
• Lon (also in mito)

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• Protein degradation in bacteria
• Also highly regulated, involves chaperone like
  proteins
• Lon
• Clp (also in chloroplasts)

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• Protein degradation in bacteria
• Also highly regulated, involves chaperone like
  proteins
• Lon
• Clp
• FtsH in IM (also in cp and mito)

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PROTEIN TARGETING All proteins are made with an
address which determines their final cellular
location Addresses are motifs within proteins
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PROTEIN TARGETING All proteins are made with
addresses which determine their
location Addresses are motifs within proteins
Remain in cytoplasm unless contain information
sending it elsewhere
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PROTEIN TARGETING Targeting sequences are both
necessary sufficient to send reporter proteins
to new compartments.
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• PROTEIN TARGETING
• 2 Pathways in E.coli http//www.membranetransport.
  org/
• Tat for periplasmic redox proteins thylakoid
  lumen!

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• 2 Pathways in E.coli
• Tat for periplasmic redox proteins thylakoid
  lumen!
• Preprotein has signal seq S/TRRXFLK

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• 2 Pathways in E.coli
• Tat for periplasmic redox proteins thylakoid
  lumen!
• Preprotein has signal seq S/TRRXFLK
• Make preprotein, folds
• binds cofactor in
• cytosol

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• 2 Pathways in E.coli
• Tat for periplasmic redox proteins thylakoid
  lumen!
• Preprotein has signal seq S/TRRXFLK
• Make preprotein, folds
• binds cofactor in
• cytosol
• Binds Tat in
• IM is sent to
• periplasm

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• 2 Pathways in E.coli
• Tat for periplasmic redox proteins thylakoid
  lumen!
• Preprotein has signal seq S/TRRXFLK
• Make preprotein, folds binds cofactor in
  cytosol
• Binds Tat in IM is sent to periplasm
• Signal seq is
• removed in
• periplasm

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• 2 Pathways in E.coli http//www.membranetransport.
  org/
• Tat for periplasmic redox proteins thylakoid
  lumen!
• Sec pathway
• SecB binds preprotein
• as it emerges from rib

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• Sec pathway
• SecB binds preprotein as it emerges from rib
  prevents folding

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• Sec pathway
• SecB binds preprotein as it emerges from rib
  prevents folding
• Guides it to SecA, which drives it through SecYEG
  into periplasm using ATP

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• Sec pathway
• SecB binds preprotein as it emerges from rib
  prevents folding
• Guides it to SecA, which drives it through SecYEG
  into periplasm using ATP
• In periplasm signal peptide is removed and
  protein folds

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• Sec pathway part deux
• SRP binds preprotein as it emerges from rib
  stops translation
• Guides rib to FtsY
• FtsY SecA guide it to SecYEG , where it resumes
  translation inserts protein into membrane as it
  is made

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Periplasmic proteins with the correct signals
(exposed after cleaving signal peptide) are
exported by XcpQ system
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PROTEIN TARGETING Protein synthesis always
begins on free ribosomes in cytoplasm
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2 Protein Targeting pathways Protein synthesis
always begins on free ribosomes in cytoplasm 1)
proteins of plastids, mitochondria, peroxisomes
and nuclei are imported post-translationally
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2 Protein Targeting pathways Protein synthesis
always begins on free ribosomes In cytoplasm 1)
proteins of plastids, mitochondria, peroxisomes
and nuclei are imported post-translationally mad
e in cytoplasm, then imported when complete
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2 Protein Targeting pathways Protein synthesis
always begins on free ribosomes In cytoplasm 1)
Post -translational proteins of plastids,
mitochondria, peroxisomes and nuclei 2)
Endomembrane system proteins are imported
co-translationally
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2 Protein Targeting pathways 1) Post
-translational 2) Co-translational Endomembrane
system proteins are imported co-translationally in
serted in RER as they are made
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2 pathways for Protein Targeting 1) Post
-translational 2) Co-translational Endomembrane
system proteins are imported co-translationally in
serted in RER as they are made transported to
final destination in vesicles
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SIGNAL HYPOTHESIS Protein synthesis always begins
on free ribosomes in cytoplasm in vivo always
see mix of free and attached ribosomes
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SIGNAL HYPOTHESIS Protein synthesis begins on
free ribosomes in cytoplasm endomembrane proteins
have "signal sequence"that directs them to RER
Signal sequence
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SIGNAL HYPOTHESIS Protein synthesis begins on
free ribosomes in cytoplasm endomembrane proteins
have "signal sequence"that directs them to
RER attached ribosomes are tethered to RER by
the signal sequence
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• SIGNAL HYPOTHESIS
• Protein synthesis begins on free ribosomes in
  cytoplasm
• Endomembrane proteins have "signal sequence"that
  directs them to RER
• SRP (Signal Recognition Peptide) binds signal
  sequence when it pops out of ribosome swaps GDP
  for GTP

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• SIGNAL HYPOTHESIS
• SRP (Signal Recognition Peptide) binds signal
  sequence when it pops out of ribosome swaps GDP
  for GTP
• 1 RNA 7 proteins

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SIGNAL HYPOTHESIS SRP binds signal sequence when
it pops out of ribosome SRP stops protein
synthesis until it binds docking protein(SRP
receptor) in RER
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SIGNAL HYPOTHESIS SRP stops protein synthesis
until it binds docking protein(SRP receptor) in
RER Ribosome binds Translocon secretes protein
through it as it is made
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SIGNAL HYPOTHESIS SRP stops protein synthesis
until it binds docking protein(SRP receptor) in
RER Ribosome binds Translocon secretes protein
through it as it is made BiP (a chaperone) helps
the protein fold in the lumen
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SIGNAL HYPOTHESIS Ribosome binds Translocon
secretes protein through it as it is
made secretion must be cotranslational