Membrane Trafficking Flashcards
How are proteins trafficked from a donor compartment to a target compartment?
- Vesicle will form on the membrane
- Will detach - budding off from the donor organelle
- Transported through the cytoplasm
- Reaches target compartment
- Vesicle then fuses with target compartment and is incorporated
What is the difference between constitutive and regulated exocytosis?
Constitutive exocytosis: Occurring all the time
Regulated exocytosis: Only happens when there is an external signal
What are protein coats needed for?
- essential for formation of vesicles
- subtle localisation where the coats operate
What are the 3 main types of protein coats?
COPI, COPII and Clathrin
What is COPI protein coat used for?
COPI coated vesicles are found in the retrograde pathway
- Going from the Golgi back to the ER
What is COPII protein coat used for?
COPII coated vesicles are the forward pathway (anterior grade trafficking)
- From ER to Golgi
What is Clathrin protein coat used for?
Clathrin - originate in the Golgi but not trafficked to the ER but elsewhere
Found in the trans golgi not the cis golgi
How are vesicles formed?
- Specific recognition event where soluble proteins will bind to membrane proteins
- Triggers recruitment of adaptor proteins
- AP1 (More than one adaptor protein involved) - Membrane curvature occurs
- Recruitment of protein coats
- Formation of the vesicle - Vesicle detaches from the donor membrane
- Protein coat detaches
- Left with a naked transport vehicle
What does AP1 do?
- an adaptor protein
- AP1 is responsible for the transport of lysosomal hydrolases between the TGN and endosomes.
What do adaptor proteins do?
AP complexes connect cargo proteins and lipids to clathrin at vesicle budding sites, as well as binding accessory proteins that regulate coat assembly and disassembly
How are vesicles shaped in the way they are?
Membrane bending proteins form BAR domain dimers
- crescent shaped
- They interact with the head groups of the phospholipids that are in the bilayer
- Interactions between them force the membrane into a curved shape
- Once curvature has happened, can recruit Clathrin
What is the shibire temperature sensitive mutation?
“the sensation when a bit of your arm goes numb when you sleep on it”
- shibire is a mutation that enables this sensation in flies
- mutation becomes apparent when the temp is shifted
What is the role of dynamin in the shibire temperature sensitive mutation?
The mutation affects membrane trafficking
- the vesicle never fully detaches and therefore is unable to release the neurotransmitters
What does Dynamin do?
pinches off vesicles from the membrane
- membranes are pushed together so much that they fuse
(other proteins involved: Synaptobrevin, Synaptotaxin and SNAP-25)
What happens in the WT of the drosophila that have the shibire mutation?
the synapse releases the neurotransmitter
- vesicles are trafficked down the neurone
- reaches surface of the cell by regulated endocytosis
- fuse with synaptic surface and release the contents
- recycling of the endosome