Transcript Getting things where they need to go: Protein Targeting

Previously Bio308
Hypotheses for molecular basis of bipolar disorder
•Suggest problem lies in protein targeting
How are proteins targeted and delivered?
3 Stages: Budding, targeting/docking and fusion
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?
Budding
Fig 17-58
http://biology-animations.blogspot.com/2009/10/clathrin-animation.html
Coat Components
Clathrin
COPI
COPII
Identity determined by what
the vesicle contains and it’s coat.
http://userpage.chemie.fu-berlin.de/biochemie/aghaucke/clath.jpg
Budding II
ER vesicle budding
Sar1p N-terminal helix
Amino Acid Key
Highly hydrophobic
+ charged
- charged
Hydroxylated
Other
Sar1p-GTP form exposes helix that
anchors protein to ER surface by
‘floating’ with hydrophobic a.a.
interacting with membrane core
Drin, G, and B. Antonny (2005) News and Views: Helices sculpt membrane. Nature vol: 437
Budding III
ER vesicle budding
Floating many Sar1p in top leaflet makes it ‘bigger’
than the bottom one.
Results --> bulge that can more easily interact with
coat proteins.
Drin, G, and B. Antonny (2005) News and Views: Helices sculpt membrane. Nature vol: 437
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
Targeting/Docking:
What happens after budding?
How do vesicles dock with specific target membrane?
http://dir2.nichd.nih.gov/nichd/cbmb/sob/in_vivo_dyn.html
The SNARE hypothesis
V-SNARE
T-SNARE
Role of p115
Role of Rab proteins
retrograde
Fig 17-59
Synaptic vesicle fusion
VAMP
Syntaxin
SNAP 25
Rab3a
Synaptotagmin
Endocytosis
Maybe protein delivered correctly but problem lies
in levels of recycling
Endocytosis can be used to control the amount of a certain
type of protein found at the surface
Pinocytosis ‘problem’
rate of pinocytosis internalizes 100% of PM per hour
?
(How can this be?)
Types of pinocytic vesicles
Clathrin-coated
Caveolae
Types of endocytosis
Fluid phase– soluble components ‘got caught’ in vesicle
Receptor-mediated– selected to be in vesicle
Select how?
•Ligands bind receptors
•Receptors cluster
Why do the receptors cluster and make a vesicle?
•Receptors have signaling sequences
•Signaling regions interact with adaptins
•Adaptins recruit coats budding occurs
Endocytosis– then what? Endosomal sorting
Separate: Recycle (R )
Degrade (L)
Transcytose
Remove and
Degrade (R & L)
Distinguishing between types
Similarities and differences between vesicles?
Transport
Exocytic
Endocytic
How could you tell them apart experimentally?
Neurotransmitters are stored in and secreted from vesicles.
Neurotransmitter receptors are delivered to
dendrite in vesicles.
Could sorting and targeting problems be
at the root of bipolar disorder?
If sorting and targeting are the problems would you
predict alteration of something like
the NT receptor, or a SNARE
or of a protein like NSF, SNAP25?
Molecular Roads and Infrastructure
Bipolar disorder
•Is it the cellular equivalent of ‘dead letter box’?
•Are cytoskeletal ‘problems’ a likely cause for
for this disorder?
What are the components of the cytoskeleton
and what do they do?