Molecular Mechanisms of synaptic vesicle recycling Flashcards
Synaptic vesicles must recycled because:
- Synapses contain a limited number of synaptic vesicles and replacing them one by one by synthesis from the cell body would be too slow.
Four pathways for retrieval of synaptic vesicle membranes
- Clathrin mediated endocytosis
explain clathrin mediated endocytosis
Slow (10 -20 secs)
What are the steps in clathrin mediated synaptic vesicle endocytosis?
• Start with synaptic vesicle fusion with the plasma membrane and releasing neurotransmitters
Describe clathrin heavy and light chain
• Self-polymerizing protein composed of three heavy and three light chains that form the clathrin triskelion
After experimenting what was found to happen when inactivation of clathrin light chain occurs?
we can completely block clathrin-mediated synaptic vesicle endocytosis.
Describe AP-2
• An adaptor that links the membrane of synaptic vesicle to clathrin and various accessory protein
Describe AP180
Adaptive protein that is capable of binding to lipids , PIP2, and clathrin. It can also regulate synaptic vesicel endocytosis.
How does the absence of the AP180 homolog in drosophila affect endocytosis?
When AP 180 is taken away there is a severe reduction in the number of synaptic vesicles and clathrin-mediated synaptic vesicles. We also see an increase in the number of cisternae/endosomes in the AP 180 mutants
Describe Dynamin
• Self-polymerizing mechsnoenzyme that triggers vesicle fission and scission upon GTP hydrolysis.
How does the absence of dynamin affect endocytosis?
• When there is a mutation in dynamin during high-frequency stimulation all the synaptic vesicles seem to be gone.
Describe endophilin
• Important in creating the right curvature for the membrane during synaptic vesicles fission and is important in recruiting dynamin or syanptoajanin
How does the absence of endophilin affect endocytosis?
We see an absence in synaptic vesicles suggesting that endophilin is required for synaptic vesicle endocytosis
When we take away these proteins what do we generally see?
When you take away clathrin, some adaptor proteins, endophilin, dynamin we block synaptic vesicle endocytosis, we see fewer vesicles But in many cases we see larger cisternae/endosomal structures.
Why is PIP 2 important?
PIP2 levels are important for the recruitment for proteins that regulate synaptic vesicle endocytosis like AP2 and AP180, Clathrin, endophilin, dynamic etc
Describe synaptojanin
• Lipid phosphatase recruited to clathrin coated pits by AP2 and endophilin
How does the absence of synaptojanin affect endocytosis?
• We see that there are very few synaptic vesicles
Describe Kiss and run
• Fast<1 sec
What is the mechanism of Kiss and Run
The synaptic vesicle will briefly open and release neurotransmitters and then close and the vesicle will pinch off the membrane; keeping the shape, protein and lipid
Describe Activity dependent bulk endocytosis
• Relatively slow (30 secs)
Compare endosomes and clathrin mediated endocytosis and at what frequency they take up HRP.
• In the lower frequencies we see primarily clathrin mediated endocytosis and they take up HRP.
During periods of high synaptic activity we will go through clathrin mediated endocytosis but endosmes will also form (T/F)
TRUE
Describe Ultrafast endocytosis
• After a single stimulus vesicle membrane is recovered at the sites latera to the fusion sites within 100 ms
Compare the 4 pathways for retrieval for synaptic vesicle membrane
Here compare and contrast the pathways, talk about speed, stimulation frequencies, and the vesicels are kept intact.
Synapses can differ greatly with respect to
- Their firing patterns
What are the 3 types synaptic vesicle pools in order of what they fire?
- Readily releasable pool
Compare the size, location and time taken to release for all three synaptic vesicle pools
- Readily releasable pool
Vesicular proteins exocytosed and subsequently retrieved by compensatory endocytosis are nonidentical
There may maybe a pool of synaptic vesicle proteins on the plasma membrane and during endocytosis there maybe pools that get mixed.
What are the different hypothetical models for sorting of synaptic vesicle proteins
- Synaptic vesicles maintain the same composition in the beginning and the end
What are the 4 ways to trigger endocytosis?
- Fused vesicles
What are the three different states a release site can exist?
• Empty and accessible for a vesicle
