Professor Uglade Lecture 12 Flashcards
(37 cards)
What is in the secretory pathway for vesicle traffic?
multiple donor and acceptor (target) membranes in secretory pathway
What are the 2 mechanisms that ensure that vesicles transport thei contents to the correct acceptor membrane?
-Rab GTPase proteins provide specificity of vesicle targeting and attachment to acceptor membrane
-SNARE fusion proteins provide specificity during fusion of vesicles with acceptor membrane
How is the golgi organized, what maintains this?
What is the old model vs the new model of vesicle transport in golgi?
-into a stack of membranes:cis, medial, trans
-cytosolic protein matrix maintains the stacks
-old model: vesicles transport cargo between layers
-new model:each layer matures and becomes the next layer
How does the new model of transport through golgi work?
-golgi resident proteins are carried backwards by COP-I vesicles
-then clathrin coated vesicles carry cargo to PM and endosomes
How are N-linked glycans modified in golgi?
-modified by removal of mannoses and addition of diff sugars, often with negative charge
How are other oligosaccharides attached?
What is many combinations of oligosaccharides called?
-attached to Ser and Thr side chains (O-linked glycosylation)
-heterogeneity
How does glycoylation promote protein folding?
-makes folding intermediates more soluble (prevents aggregation)
-sequential modificatoins–>Glyco-code–>progression folding or degeneration
How does sugars having limited flexibility aid the golgi?
What else does glycosylation contribute in golgi function?
-they protect from proteases, stabilizes protein structure (protective coat)
-it is a signaling hub (regulation of development)
What happens to the some PM and extracellular proteins that are made as longer inactive forms in the ER?
WHat do proprotein convertases/proteases recognize?
-they are cut by proprotein convertases into shorter active forms in the golgi
-they recognize the pattern of amino acids and cleave to get rid of inhibitory part, to make the protein active
How is proinsulin an example for proprotein convertase use?
-Proinsulin is made as one inactive polypeptide, to prevent premature signaling by insulin at the ER
-convertases remove the middle section, the 2 remaining sections form active insulin
How do proteases regulate the golgi traffic?
ATF6 is activated by converyase proteolysis in the Golgi
-regulation is by trafficking
-BiP covers ER exit signalon ATF6, and proteases are only in the golgi
What are Rab-proteins?
What type of things in the cell have sets of rab proteins?
-large subfamily of Ras-related proteins
-different organelles and vesicles types in the secretory pathway have unique sets of Rab proteins
What are Rab proteins turned on and off by?
What does Rab-GTP bind?
-switched on by GEF, switched off by GAP
-RAB-GTP binds to a large number of rab effector proteins which mediate vesicle targeting
Where do Rab proteins act in?
What do they assist with and connect?
-Rabs can act at several steps in vesicle targeting
-they assist cargo selection and coat formation during vesicle budding
-they connect vesicle to motors on cytoskelton for transport
(diff rab is used in each step)
What do Rabs thether and recruit?
-they thether vesicles to the acceptor membrane for specificity
-they recruit SNARE fusion proteins
What are Rabs composed of/where?
What is Rab in the GDP-bound state?
what hides the lipid and prenyl group?
-rabs have 2 prenyl lipid groups attached at their C-termini (prenylation)
-In the GDP bound state Rab is soluble and not associated with the membrane
-lipid and prenyl group is covered up by other proteins (GDI, GDF) when interacting with Rab
What happens to Rab in the GTP-bound state?
What happens to the Rab effector proteins?
-the lipid modifications are exposed and anchor Rab to the membrane
-the Rab effector proteins become attached to the membrane through Rab-GTP
How is Rab activated?
A specific GEF on membrane produces anchored, active Rab-GTP
-GEF is linked to the formation of vesicle coat
How does Rab-GTP work through effector proteins?
How is more Rab-GTP made?
-attaches vesicle to motor proteins
-tethers vesicle to target membrane
-activates PI kinases and GEFs to make more Rab-GTP in clusters on acceptor membrane
1.What activates vesicle Rab, what does Rab interact with?
GEF on the donor membrane activates GEF and packages onto vesicles
-some interact with cargo, assist uncoating, or attache motors
2.What happens after Rab is activated, where does it bind?
-vesicle Rab-GTP binds specifically to tethers on acceptor membrane
What occurs after Rab tethering on acceptor membrane?
-after fusion to membrane, GAPs (GTPase-activating proteins) on target membrane inactivate Rab
What happens in vesicle Rab cycle after Rab is inactivated?
inactiavted vesicle Rab-GDP is recycled through cytosol to donor membrane
what provides structure to the cells?
cytoskelton-protein filament (actin) and microtubules (tubulin) run through cytosol and provide strcuture to cells
