Intracellular Vesicular Traffic

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Chapter 13

• Intracellular Vesicular Traffic

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The molecular mechanisms of membrane transport
and the maintenance of compartmental diversity
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GFP-FUSION PROTEINS HAVE REVOLUTIONIZED THE STUDY
OF INTRACELLULAR TRANSPORT
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There are various types of coated vesicles
Mediate transport from Golgi from plasma
membrane
Mediate transport from ER Golgi
Each type is used for different transport steps
in the cell.
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The assembly of a clathrin coat drives vesicle
formation
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by charperone (hsp70)
Major coat protein clathrin adaptin
There are at least four types of adaptins, each
specific for a different set of cargo receptor.
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• Both the pinching-off and uncoating of coated
  vesicles are regulated processes

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• Not all transport vesicles are spherical

? Various size shape
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Monomeric GTPase control coat assembly
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• SNARE proteins and targeting GTPases guide
  membrane transport

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Trans-SNARE complex
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Interacting SNAREs need to be pried apart before
they can function again
cytosol
Cycle
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Rab proteins (monomeric GTPase) help ensure the
specificity of vesicle docking
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Rab facilitate docking of transport vescicles.
Rab its effector ?Structure vary
greatly ?Function common (1.concentrate
tether vesicle near target site 2. Trigger
release of SNARP control protein)
cycle
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SNARE may mediate membrane fusion
Process for SNARE concentrate in membrane fusion
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• Viral fusion proteins and SNAREs may use similar
  strategies

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Transport from the ER through the golgi apparatus
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ER exit site
50nm vesicle gt 200 mem protein
Cargo Recruitment
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Only proteins that are properly folded and
assembled can leave the ER
Incomplete
ER resident protein
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CF (Cystic fibrosis) Defect in Cl-
transport This is not because the mutation
inactivated the protein, But because the active
protein is discarded before it reaches the
plasma membrane.
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Transport from the ER to the Golgi apparatus is
mediated by vesicular tubular clusters.
Heterotypic fusion
Homotypic memb fusion is not restricted to form
VTC.
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The structure formed when ER-derived vesicles
fuse with one another are called.
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ER retrival signal
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The retrieval pathway to the ER uses sorting
signals
Lys-Asp-Glu-Leu (KDEL)
Short retrieval signal at c-terminal
Resident ER membrane protein
KKXX at c-terminal end ? direct interact with
COPI coat
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• Many proteins are selectively retained in the
  compartments in which they function

Aggregation of proteins that function in the same
compartment - called kin recognition
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The golgi apparatus consists of an ordered series
of compartments.
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Two major classes of N-linked oligosaccharide
complex
High mannose
No new sugar added in Golgi
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Oligosaccharide processing in ER and Golgi
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High specific endoglycosidase
Can distinguish between these two type
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• Proteoglycans are assembled in the Golgi Apparatus

O-linked glycosylation
Proteoglycans are secreted or anchored to plasma
membrane
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• What is the purpose of N-glycosylation?

1. N-linked is prevalent in all eukaryotes, but
absent in procaryotes. 2. limited flexibility. 3.
Recognition 4. Regulation of development 5.
Protective coat unit 6. Cell-cell adhesion
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N-linked
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The golgi cisternae are organized as a series of
processing compartments
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Functional compartmentalization
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• Matrix proteins form a dynamic scaffold that
  helps organize the apparatus

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Transport from trans golgi network to lysosomes
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Lysosome are the principal sites of intracellular
digestion
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Lysosomes are heterogeneous (morphology)
The diversity reflects the wide range of
digestive function.
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Plant and fungal vacuoles are remarkably verstile
lysosomes
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Controlling size
Vacuole function Storage, degrade, cell size,
turgr pressure, homostatic device
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Three pathways to degradation in lysosomes.
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M6P receptor recognizes lysosomal proteins in
the Trans Golgi network (TGN)
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The M6P receptor shuttles between specific
membranes
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Transport into the cell from the plasma membrane
endocytosis
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Transport from the trans golgi network to the
cell exterior exocytosis
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Chapter 13 practice

1. The endocytic and biosynthetic-secretory and
   retrieval pathway.
2. Utilization of different coats in vesicular
   traffic.
3. The role of SNAREs and SNAREs-interacting
   proteins in vesicle transport .
4. The traffic role of COPI COPII coat shuttling
   between Golgi and ER.
5. What is KDEL signal and its role in retrieval
   pathway.
6. How to distinguish between the high-mannose
   oligosaccharide and complex oligosaccharide.
7. Write the full name for Glc NAc, NANA(sialic
   acid).
8. The functional compartmentization of Golgi
   apparatus.
9. Three pathways to degradation in lysosomes.
10. How to transport lysosomal enzyme to lysosome
    from ER.
11. Possible fates for endocytosed transmembrane
    receptor proteins.
12. The receptor-mediated endocytosis of LDL.
13. Three best-understanding pathways of protein
    sorting in trans Golgi.