Lecture 10 - The Active Zone Flashcards
Where is the active zone?
is an electrin dense region at the presynaptic membrane - get signal via em where very proteinacious or electron dense
What are the four major functions of the active zone?
- docking and priming of synaptic vesicles - docked means bring them close to the membrane and prime makes them ready for fusion molecularly
- recruit and stabilize voltage gated calcium channels to the presynaptic membrane - allows for fast excitation and coupling
- coordinate pre and post synaptic alignment through trans synaptic cell adhesion proteins
- mediate much of the short and long term presynaptic plasticity - either directly through secondary messengers like caclium or dag or indirectly through recruiting effects
What role do actuve zone play in synaptic transmission?
actuve role - modulate NT release and response to AP through dociking and priming anf calcium channels and transcynaptic alignment and LTP
What are the three major structures that the EM labels?
- synaptic vesicles
- dense projections like AZ proteins
- postsynaptic compartments
If you take an EM cross section at the NMj what will you see?
a dense projection of a T bar surrounded by synaptic vesicles
What is the dense projection of a c elegan like?
thin and wispy
What is the dense projection of the NMJ in fly?
T-bar with synaptic vesicles
What is seen in ribbon synapse of goldfish photorecptor?
many synaptic vesicles
What is seen in EM of central synapse?
underdeveloped dense projection and not many SV cause only releases like one at a time
What are the five evolutioanruly conserved proteins that make up the active zone?
- RIM - RAb3 interacting molecule
- unc13/dunc13/munc13
- Liprin/alpha
- RIM-BP
- ELKS
What is found in the actuve zone?
-calcium channels
-elks
-rim-bp
-rim
-liprin-alpha
-unc13/dunc13/munc13
What happens if you delete one active zone protein?
nothing much since there is great redundancy built into the system
Why do all of the active zone protein interact with each other via binding domains?
to make a stable resilient molecular scaffolding machine primed for efficent sv fusion
What are RIM proteins?
the central organziing moelcule of the active zone
What are the three roles of RIM?
-SV docking and priming
-recruit calcium channels to actuve zones
-short term plasticity
What domain of RIM binds to unc13 for positioning synapses for vesicle fusion aka docking and priming?
C2 domain
What domain of RIM binds ELKS and calcium channels for calcium posiitoning cause elks helps with calcium channel posiitoning and how many syanptic vesicles are at atcive zone?
PDZ domain
What does the zinc finger domain of RIM do?
takes synaptic vesicle and brings it to unc13 for priming and docking
What else do the PDZ and C2A and C2B domains do?
bind calcium for plasticity short term
In the PDZ domain of RIM what portion of the calcium channel does it interact with to bring calcium channels to active zone?
cytosolic tail
What does RIM-BP do?
links rim to calcium channels
How does rim-bp allow for reduncnay in actuve zone?
it can also bind the cytosolic tail of calium channels
What does munc-13 do?
synaptic vesicle priming -primes snare proteins for vesicle fusion
-short term plasticity via priming
-positions synaptic vesicles fusion sites in the active zone
-also has a calcium binding domain and secondary messenger site
What does liprin alpha do?
meditaes binding of elks/rim to cell adhesion molecules
-helps to establish where and when active zones are formed
What is the earliest actuve zone protein?
liprin alpha and it also binds to transsyanptic molecules like PTP and LAR
What are the two functions of elks?
-needed for determining how many synaptic vesicles are at the active zone docked and primed
2. anchors and positions calcium channels
-spans the membrane into the cytosol
What is an ideal system to study the active zone and what is used to do this?
drosophilia NMJ
-light microscope
-can see T bar with synaptic vesicles and can see that the postsyanptic receptors and active zone are colocalized
What forms the T-bar at the active zone?
BRP which is the drosophilia elks homolog
What microscopy revelaed the T bar is a doughnut?
STED microscopy which is a high resolution light microscopy
What happened to brp mutants?
cant fly so die
What is clustered at the center of BRP?
calcium channels
What is the model of the drosophila active zone?
-calcium channels about five center in the middle and and brp anchored one end in plasma membrane to organize calcium channels and one end in cytosol to anchor synaptic vesicles
Where are synaptic vesicles patterned in the presynaptic active zone?
outside of the highest devsity of actuve zone componenst
What is distrubuted throughout the synaptic cleft and where is the highest density of it?
proteinacious material and it has the highest density in the outer ring and it has cell adhesion porteins like ephrin LAR and neurexins which allow for transsynaptic alignment
What is the patterning of postsyanptic densoty?
clusters of receptors found opposute rim and rimbp so active zone
What are the three proposed mechanisms for synaptic alignment?
1.transsynaptic molecule at pre and post synaptic site
2. calcium channels and post synaptic receptors interact
(glycosylated ec proteins can link calcium channel to glutamate receptor)
3.glutamate itself can cause receptor apposition or retrograde signals from the postsyanptic cell too
