Lect. 13 - Intracell Vesicular traffic Flashcards
What 2 major functions does the coat perform?
concentrates select proteins in a specialized patch for transport; molds the vesicle to form basketlike lattice that deforms the membrane and gives shape to the vesicle
make up of clatherin subunit
3 large and 3 small polypeptide chains that form a 3-legged structure called triskelion
triskelion
assemble into a basket-like structure of hexagons and pentagons that form coated pits on the cytosolic side of membrane
adaptor proteins on clatherin coated vesicles
form a second layer under the clatherin and trap various transmembrane proteins including receptors for soluble cargo
assembly of clathrin coat
introduces a curvature in the membrane which leads to the formation of coated buds
PI (phosphoinositides) role
can undergo rapid cycles of phosphorylation and dephosphorylation at the 3’, 4’, and 5’ positions; they control recruitment and binding of proteins to specific organelles/domains and regulate vesicle trafficking
what part of the PIs are recognized by proteins?
headgroups
dynamin
protein that assembles a ring around the clatherin bud; contains a PIP2 binding domain and GTPase domain
PIP2 binding domain on dynamin
tethers the protein to membrane
GTPase domain on dynamin
regulates rate of vesicle pinching
pinching
brings the 2 cytosolic sides of the membrane together and allows them to fuse
aside from forming a ring around the clathrin vesicle, what does the dynamin do?
recruits other proteins that distort the lipid bilayer (ex. lipid modifying enzymes)
what chaperone is uses ATP to peel off the clathrin coat?
Hsp 70
Rab proteins
monomeric G protein that direct vesicle to specific spots on the target membrane
SNARE proteins
mediate fusion of vesicle w/ membrane
how is specificity in targeting of vesicles achieved?
by surface markers on vesicles and complementary receptors on target membrane
what regulated the activity of Rab?
GTP hydrolysis
what is Rab bound to in the inactive form?
GDP (soluble form)
what is Rab bound to in the active form?
GTP
What keeps Rab in the inactive form?
binding to Rab-GDP dissociation inhibitor (GDI)
what keeps Rab in the active form?
interaction w/ Rab-GEFs. tightly bound to a membrane
Rab effectors
motor/tethering proteins that is present on the target membrane that the active form of Rab binds to
Rab1
ER and Golgi complex
Rab2
cis Goli network
Rab3A
synaptic vesicles, secretory vesicles
v-SNAREs
single polypeptide; found on VESICLE membrane
t-SNAREs
2-3 proteins; found on TARGET membrane
interaction b/w the v and t forms of SNAREs
allow them to wrap around eachother to form a bundle; lock the two membranes together
what proteins are packaged into COPII?
newly synthesized
where do COPII coated transport vesicles bud off from?
from the ER exit sites
what chaperones are involved in misfolded proteins to keep them retained in the ER
BiP or calnexin
homotypic
fusion of vesicles from SAME compartment
heterotypic
fusion of vesicles from DIFFERENT compartments
vesicular tubular clusters
fused structures resulting from vesicles that have released from the ER and fused
COPI
vesicular tubular clusters bud off to form smaller vesicles that are coated w/ COPI to return proteins to the ER
what is the retrieval pathway dependent upon?
ER retrieval signals
what is the retreival sequence present in the ER membrane?
KKXX sequence
what is the retrieval sequence present in soluble proteins?
KDEL sequence
KKXX signal
interacts w/ COPI and packaged into COPI-coated vesicles
What is needed for soluble proteins to package them into COPI-coated vesicles?
KDEL receptor
golgi apparatus
collection of flattened, membrane-enclosed compartment (cisternae); plays important role in protein glycosylation; each golgi stack has 2 faces: cis/entry and trans/exit
Cis Golgi Network (CGN)
network of fused vesicular tubular clusters arriving from ER. Proteins and lipids enter Golgi via CGN
Trans Golgi Network (TGN)
region that allows exit of proteins and lipids to next step of secretory pathway
which face of the golgi apparatus is closer to the ER?
cis face
