Zaidi Vesicular Traffic 1 Flashcards
The function of transport vesicles…
is to transport proteins and other biomolecules
Vesicles __ __ from primary compartment and __ with the next one.
bud off
fuse
Contents of a vesicle are called…
cargo
Transport is…
directional
__ mediates a continuous __ of components between various membrane enclosed compartments.
vesicular transport
exchange
Cues for incoming traffic are provided by what two things?
composition of the membrane, molecular markers on membrane surface
Like a zip code, __ of __ gives each compartment its full molecular address.
combination of markers
Retrieval pathways
return molecules to their source
How do cells segregate proteins in to membrane domains?
By assembling a special coat on the cytosolic side of the membrane.
transport vesicles bud off as __ vesicles
coated
What are the two major functions of the vesicle coat?
- concentrates select proteins in a specialized patch for transport.
- coat molds the vesicle to form a basket like lattice that deforms the membrane and gives shape to the vesicle
The vesicular coat is discarded…
before the vesicle fuses with target membrane
Name the three types of coated vesicles:
COPI
COPII
Clathrin-coated
COPI vesicles mediate transport from the __ __, while COPII mediates transport from the __. Clathrin coated vesicles mediate transport from __ __ and from __ __.
Golgi cisternae
ER
Golgi apparatus
plasma membrane
The major protein of clathrin-coated vesicles is __.
Each clathrin subunit contains 3 large and 3 small ___ ___ that form a 3 legged structure called a __.
polypeptide chains
triskelion
Triskelions assemble into __-__ structure of __ and __ that form coated pits on the cytosolic side of the membrane.
basket-like
hexagons
pentagons
The second layer between the cage and the membrane of clathrin coated vesicles is formed by…
These proteins trap various transmembrane proteins including receptors that capture ___ ___ inside vesicle
adaptor proteins
soluble cargo
Describe the process of clathrin coat assembly and disassembly.
1 assembly of coat protein molecules introduces a curvature in the membrane.
2 leads to the formation of coated buds.
3 adaptor proteins bind clathrin and membrane-bound cargo receptors.
4 selective recruitment of membrane and cargo molecules in vesicle.
5 clathrin coat lost after vesicle formation completed
Phosphoinositides
Phosphoinositol
play a major role in coat assembly, vesicle formation, and protein trafficking
a phospholipid that helps with membrane process
slide
18
Bar domains serve as
membrane bending proteins
(coil-like proteins) coiled coils which dimerize into domains
Dynamin:
It contains __ and __
protein that forms a ring around a clathrin bud
PIP2 binding domain (tethers the protein to membrane) and GTPase domain (regulates rate of pinching)
Pinching
brings the 2 cytosolic sides of the membrane closer together and allows them to fuse
Proteins recruited by dynamin to distort the lipid layer do so by
modifying enzymes that change lipid composition
PIP2 is degraded when … which weakens the binding of …
vesicle loosens clathrin coat
adaptor proteins
HSP70
chaperone protein that peels off clathrin coat with the use of ATP
specificity is achieved by what on vesicles and what on target membrane?
surface markers
complementary receptors
What two proteins play a role in specificity? What are the functions of each?
Rab proteins- direct vesicle to specific spots on target membrane
SNARE proteins- mediate fusion of vesicle with membrane
Rabs are __ __ (~60) whose activity is regulated by ___ ___.
It cycles through __ and __ and regulates reversible assembly of complexes on the __.
monomeric GTPases.
GTP Hydrolysis.
cytosol, membrane, membrane
Rab is inactive in the ___-bound form and active in the __-bound form.
Binding with Rab-__ __ __ keeps it in the inactive GDP-bound form that is soluble.
Interaction with Rab-__ keeps it in an active GTP- bound form tightly bound to a membrane.
The active form binds to Rab ___ (motor proteins or tethering proteins) present in the target membrane.
GDP, GTP
GDP dissociation inhibitor
GEF
effectors
Subcellular locations of Rab Proteins:
Rab 1
Rab 3a
Rab 5
ER and Golgi complex
synaptic vesicles, secretory vesicles
earyl endosomes, plasma membrane, clathrin-coated vesicles
there are # different SNARE Proteins, each associated with a different compartment.
They exist as ___ sets.
__-snares (single polypeptide) are found on vesicle membrane
__-snares (2-3 proteins) are found on target membranes
Interaction between the two forms of snares allows them to … which locks the 2 membranes together.
Fusion may be triggered by specific ___ signals which may remove inhibitory signals which may remove inhibitory proteins that prevent complete fusion.
35
complimentary
V
T
wrap around each other forming a bundle
extracellular
What are the three steps of docking and fusion of a vesicle?
1 tethering
2 docking
3 fusion
recycling of SNAREs
SNAREs are detangled by NSF which utilize ATP to separate SNAREs to make them available for another capture
Newly synthesized proteins are packaged into __ __ transport vesicles which bud off from ER __ __.
Proteins display __ __ on their cytolsolic surface which are recognized by receptors present on the __ coat.
Describe Quality control
COPII coated
Exit sites
exit signals
COPII
Incompletely folded or misfolded proteins are retained in ER by bindinig to chaperone proteins such as BiP or calnexin and are degraded.
Vesicles fuse with each other after…
budding from the ER exit sites and shedding their coat
Contrast Homotypic and Heterotypic
Fusion of vesicles from same compartment versus fusion of vesicles from different compartments.
Fusion of vesicles requires ___, with both membranes contributing _- and _-____ to form…
SNAREs
v and t snares
vesicular tubular clusters
Retrieval Pathway
Process for returning proteins to ER from Golgi based on ER retrieval signals.
Large vesicles bud off to form smaller vesicles coated with COPI.
Compare and contrast KKXX and KDEL sequences
Both are ER retrieval signals that are packaged into COPI coated vesicles
KKXX is present in ER membrane proteins, interacts with COPI
KDEL is present in soluble proteins that require a KDEL receptor to be packed into COPI vesicles
Golgi Apparatus
Collection of flattened, membrane-enclosed compartments called cisternae.
2 faces: cis (entry) and trans (exit)
Plays an important role in glycosylation
The ______ is a network of fused vesicular tubular clusters arriving from the ER. Proteins and lipids enter Golgi via this.
The _____ is the region that allows exit proteins and lipids to next step of secretory pathway.
Cis Golgi Network (CGN)
Trans Golgi Network (TGN)
