1.11: Protein Sorting - Glycosylation and Vesicles Flashcards
most soluble and tm proteins in the er are __________ (which modification)
glycosylated
what are the two types of glycosylation and which is more common
- o linked glycosylation
- n linked glycosylation
n linked more common
- the atom means that that is where it links to the side chain of aa ef sugar group linked to the n of aa side chain (specifically N on ASN)
which oligosaccharide precursor is preformed in the er
n linked oligosaccharide
list the 3 components of n linked oligosaccharides
n-acetylglycosamine, mannose, glucose
what transfers the the n linked oligosaccharide precursor and to where
n linked oligosaccharide precursor is transferred by an oligosaccharyl transferase to an asn on a protein being synthesized
asn-x-ser or asn-x-thr is where oligosaccharyl transferase can link an n linked oligosaccharide, x can be any aa except ?
proline
proteins are only glycosylated on the __________ side
er lumen side
what are the names of the 3 cisternae in the golgi
(from er) cis, medial, and trans (to lysosome, pm, secretory vesicle)
*each cisternae have different [enzymes] which can remove or add sugars resulting in diff mods to diff prot
describe the processing of n linked oligosaccharides in the er
after the transfer of the n linked oligosaccharides to the protein:
1. 3 glucoses removed (one at a time) - this is linked the the proper folding of the protein
2. 1 mannose removed
(step 1 and 2 are the signal for 3)
3. glycosylated protein is transported via vesicles to the golgi
explain why are proteins glycosylated?
- tag to mark the state of protein folding
- protect proteins on the cell surface from proteases
- some glycosylated proteins have a role in cell adhesion
- allows proteins to form the correct 3d structure
describe how glycosylation can be a tag to mark the state of protein folding
the prot (w precursor oligosaccharide) comes into er lumen and is unfolded. glucose trimmed (2). before glucosidase II can remove the final glucose, calnexin (chaperone to help folding) binds to the remaining glucose). glucosidase II removes the final glucose + mannosidase does it’s job. the protein can exit from er through vesicular transport if normally folded. if incomplete folding, then glucosyl transferase takes upd glucose and cuts udp to add glucose again to allow calnexin to try again. the cycle repeats.
some cargo proteins are bound by _____________
transmembrane cargo receptors (but these aren’t considered as cago themselves)
t/f only nascent transport vesicles have protein coats, old ones don’t
true
what are the functions of protein coats?
- select cargo for vesicle
- give curvature to vesicle
- promote vesicle budding
what do the following protein coats do (where they send cargo between)
i. copI
ii. copII
iii. clathrin coated vesicles
i. copI: from golgi to er, between diff golgi cisternae
ii. copII: from er to golgi
iii. clathrin coated vesicles: from golgi and pm to endosome
vesicle formation involves monomeric ______
gtpases
what are monomeric gtpases regulated by
-gef (guanine nucleotide exchange factor): catalyzes gdp and gtp binding
- gap (gtpase activating protein): gets it to turn off through gtp hydrolysis
describe the general steps in coat assembly and vesicle formation
- gef at site of membrane budding: recruits gtpase –> gtp bound (=on)
- gtp-gtpase recruits coat proteins
- vesicle bud formation, cargo selected
- vesicle buds off
- vesicle uncoating: copI and copII coated vesicles involve gaps but clathrin viescles have diff mech
now vesicle is ready for transport to the target compartment
t/f do arf and sarI have the same mechanism
yes
does arf or sar1 gtpase go with each of the vesicle coats
copI and clathrin = arf gtpase
copII = sar1 gtpase
to have inactive, sar1/arf gdp, the amphipathic a helix is exposed or not exposed
not exposed
describe the formation of copII-coated vesicles
- sar1-gef in er membrane recruits sar1
-sar1-gtp has amphipathc a helix exposed and it can interact w membrane - recruits coat protein subunits to be inserted
what 3 things do coat proteins need to select
- cargo (eg tm prots)
- tm cargo receptors
- snares
what is the diff between inner and outer layer of vesicle coats
- inner layer binds to membrane and selects cargo
- outer layer associates w the inner layer to promote polymerization of the coat (sometimes also selects cargo)
for copI coated vesicles:
- how many inner and outer subunits
- how to uncoat
- inner 4 subunits
- outer 3 subunits
- select specific cargo
- uncoat: y COP binds to Arf GAP, gtp hydrolysis (arf gtp -> arf gdp (no more exposed amphipathic a helix), arf gdp detaches from membrane (after prot also leaves) and coat is released
for copII coated vesicles:
- how many inner and outer subunits
- how to uncoat
- inner 2 subunits (sec23/sec24)
- outer 2 subunits (sec13/sec31)
- select specific cargo
- uncoat: sec23 has gap activity and is stimulated by sec13/sec31, gtp hydrolysis (sar1gtp -> sar1gdp), sar1gdp detaches from membrane and coat is released
for clathrin coated vesicles:
- how many inner and outer subunits
- how to uncoat
- inner diff adaptor complexes
- outer clathrin (6 subunits)
- select specific cargo
- pinching off of vesicles req dyamin (has gtpase activity)
- uncoat: req hsp70 (chaperone) and auxilin (helper)
for clathrin molecule, ________ polymerize to form a curved lattic
triskelions
as vesicles need to fuse with the correct target membrane, specificity is determined by:
- proteins for docking and tethering the vesicle to the target membrane (monomeric rab gtpases and rab effectors)
- proteins for catalyzing vesicle fusion w the target membrane (snares (tm prot))
how to rab gtpases and rab effectors mediate vesicle docking
- rab gtp binds rab effector (many diff kinds)
- rab gtp + rab effector dock and tether vesicles, v-snares and t-snares are brought together
what do v and t of vsnare and tsnare mean (these two binding promotes membrane fusion)
v is vesicle membrane snare and t is target membrane snare
t/f is there specificity in the interaction between v and t snares
yes
in SNARES, _______ domains coil around each other and lock two membranes tgt
helical
what is needed to dissociate snare complex
nsf and adapter proteins unravel helical domains of snares
describe vesicle fusion in terms of snares
the v snares and t snares of nearby vesicles associate. they bring the vesicles so close tgt where is there is no more movement of water. they form a stalk and cytosolic leaflets form tgt first. then noncytosolic leaflets through hemifusion. then complete fusion to allow the vesicle contents to be transferred
v-SNAREs and t-SNAREs bring membranes _____ together, _______ water, and promote _________ fusion
v-SNAREs and t-SNAREs bring membranes close together, displace water, and promote membrane fusion
In COPA syndrome, the α subunit in the COPI coat does not function correctly.
This is a very rare disease, affecting approximately 100 people worldwide.
However, many people have diseases with very similar symptoms.
Which of the following patients will have symptoms that MOST resemble
COPA syndrome?
A. A patient with a dynamin mutation.
B. A patient with a COPII mutation.
C. A patient with a β’-COP mutation.
D. A patient with an ARF-GEF mutation.
C
