Previously Bio308

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Previously Bio308

• Hypotheses for molecular basis of bipolar
  disorder
• Suggest problem lies in protein targeting
• How are proteins targeted and delivered?

Sorting places proteins in membrane and in lumen
of organelles
PM (and other) proteins use Sec or SRP mediated
translocation to become inserted into the ER
(and only the ER) After insertion non-ER
proteins are sorted and delivered sorting
lumenal vs membrane proteins how?
http//www.udel.edu/Biology/Wags/histopage/empage/
ebv/ebv10.gif
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ER proteins
ER
Where can a protein end up in the ER?
How does it get there?
What category do our neurotransmitter and
neurotransmitter receptor fall in?
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How do you get soluble lumenal proteins vs Type
III
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Getting out of the ER
ER
Now what?
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Vesicular traffic
Secretory pathway also method for delivering new
PM proteins
ER to Golgi to trans-Golgi network ? then
constitutive or regulated exocytosis
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Constitutive and Regulated Exocytosis
Constitutive constant, sometimes called bulk
flow
Constitutive does not mean un-regulated
Regulated needs additional signal to initiate
fusion of vesicle with PM
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Stages of vesicle traffic
3 Stages Budding, targeting/docking and fusion
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Consequences of unregulated vesicular traffic
Mixing of organelle contents (? wont function
correctly)
Mislocalization of proteins (? wont function
correctly)
Inappropriate levels of secretion (too hi or too
lo)
A Dead Cell
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Vesicular traffic control
Our neurotransmitter receptor need to go
through 5 cellular compartments before it gets
to the post synaptic membrane
How does a vesicle know what components it
should contain?
How does it know which membrane it should go to?
How does it fuse when it gets there?
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Content selection
What goes inside which vesicle?
Lumenal protein
Transmembrane proteins
Combination of cytosolic and lumenal proteins
determine specific vesicle content
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Budding
http//biology-animations.blogspot.com/2009/10/cla
thrin-animation.html
Fig 17-58
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Coat Components
Clathrin COPI COPII
Identity determined by what the vesicle contains
and its coat.
http//userpage.chemie.fu-berlin.de/biochemie/agha
ucke/clath.jpg
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Budding II
ER vesicle budding
Sar1p N-terminal helix
Amino Acid Key
Drin, G, and B. Antonny (2005) News and Views
Helices sculpt membrane. Nature vol 437
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Budding III
ER vesicle budding
Floating many Sar1p in top leaflet makes it
bigger than the bottom one. Results --gt bulge
that can more easily interact with coat proteins.

Drin, G, and B. Antonny (2005) News and Views
Helices sculpt membrane. Nature vol 437
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Fission
ER vesicle budding.fission
Ring of parallel helices at neck might aid
fission. New data for ER had seen a protein
(epsin) help deform PM for clathrin coated
vesicles. May suggest that using a helix to
deform membrane is common mechanism for
budding/fission
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Targeting/Docking
What happens after budding? How do vesicles dock
with specific target membrane?
http//dir2.nichd.nih.gov/nichd/cbmb/sob/in_vivo_d
yn.html
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The SNARE hypothesis
V-SNARE
T-SNARE
Role of p115 Role of Rab proteins
retrograde
Fig 17-59
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Synaptic vesicle fusion
VAMP
Syntaxin SNAP 25
Rab3a
Synaptotagmin
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Next Moving in the other direction endocytosis
Types Phagocytosis specialized cells
Pinocytosis all cells
Connection perhaps the of our receptors on
PM is controlled by endocytosis
Pinocytosis problem rate of pinocytosis
internalizes 100 of PM per hour
? (How can this be?)