Lecture 19; Synaptic Plasticity 1

Question 1

Describe AMPA regulation;

Answer 1

LTP and LTD reflect bi-directional and symmetrical regulation of AMPARs:

Therefore; Bidirectional receptor regulation in plasticity

Question 2

Describe the localisation of post synaptic receptors;

Answer 2

AMPA and NMDA are localised to the tip of the post synaptic clefts, NOT on the sides

At a very specific part of the membrane as is the PSD

Question 3

What is located under the post synaptic membrane?

Answer 3

The post synaptic density (PSD)

Question 4

Describe the PSD in excitatory neurons;

Answer 4

In excitatory neurons the PSD is thick (hallmark feature)

I.e post synaptic excitatory glutamatergic neurons

Thinner in inhibitory PSDs

Question 5

Describe the PSD;

Answer 5

• Specialisation of the postsynaptic membrane - high concentration of proteins–estimate ~1000 proteins
• Made up of receptors, scaffolding proteins, transduction proteins, trafficking proteins

Question 6

How can you differentiate the post synaptic density from the pre synaptic density?

Answer 6

The presynaptic density has lots of vesicles containing neurotransmitter

Question 7

Describe some of the key properties of PSD proteins;

Answer 7

• Almost all have multiple domains
• Domains act as protein-protein binding sites in a reversible manner creating a plexus
• Share properties

Binding is essential for the density

Question 8

What is the most famous PSD protein?

Answer 8

PDZ domains

Question 9

Whats so special about the PDZ domain?

Answer 9

–PDZ-domains bind to each other
–Present in most PSD proteins
–Bind the C-terminal tails of glutamate receptors

Question 10

What is the equivalent PSD on the presynapse?

Answer 10

Proteins form an action site on the presynapse

Question 11

What do the PSD protein domains allow?

Answer 11

• Allowing protein protein interactions
• Protein receptor interactions
• Protein linking back to cytoskeletal interactions

Question 12

What is the design of the PSD for?

Answer 12

Intricate design to allow high density of proteins and to traffic receptors to the membrane

Question 13

What binds to the glutamate receptors?

Answer 13

C terminal of the glutamate receptors contains a PDZ domain and binds PDZ in the PSD.

Stabilises the receptors

Question 14

What are some key PSD proteins?

Answer 14

SAP97
GRIP
SHANKS

Question 15

Describe SAP97;

Answer 15

Synapse Associated Protein 97kDa

Binds directly to both AMPA and NMDA receptors (rare to bind both)

Question 16

What is the function of SAP97 according to biochemistry?

Answer 16

• trafficking receptors from the soma to the synapse

* Maintaining the structural integrity of the PSD through protein-protein interactions

Question 17

What is unique about SAP97?

Answer 17

It traffics both AMPA and NMDA but in two distinct ways (essential for plasticity)

Question 18

What makes receptor trafficking difficult?

Answer 18

neurons are polarised

Question 19

Describe the binding of SAP97;

Answer 19

PDZ domains important in protein:protein interactions

AMPA PDZ one of SAP97
NMDA PDZ two of SAP97

Question 20

What does GRIP consist of?

Answer 20

Entirely PDZ domains (only one)

Question 21

What is the function of GRIP?

Answer 21

-GRIP is known to be critical in the removal of AMPA receptors from the postsynaptic membrane during LTD

Question 22

What are SHANKS also known as?

Answer 22

A master regulator. Critical protein in PSD. Binds many other proteins

Can bind directly or indirectly to glutamate receptors

Question 23

What is special about shanks?

Answer 23

It has the most binding partners.

Multidomain

Question 24

Where are shanks location in the PSD?

Answer 24

-Lie in the middle of the PSD and form a scaffold across the PSD

SAM domain is important for this parallel structure

Question 25

Why are shanks known as the master regulators?

Answer 25

-Due to their ability to form complexes with receptors, signalling molecules and the cytoskeleton, Shanks are thought of as “master regulators” of the synapse

Question 26

What are the five possible roles of PSD proteins?

Answer 26

1) Structural Role
2) Trafficking receptors to the synapse
3) Inserting receptors into the membrane
4) Signaling molecules
5) Removing receptors from the membrane

Question 27

How do PSD proteins play a structural role?

Answer 27

–Through domains PSD proteins can interact with each other and form tight bonds that link to actin cytoskeleton

Maintains structure when receptors are added or removed

Very specific linkages for this

Question 28

How do PSD proteins play a trafficking role?/ describe receptor trafficking

Answer 28

1. Receptors are synthesised in the soma and assembled in the ER and Golgi
2. Significant trafficking of glutamate receptors must occur along dendrites to supply synapses

Chaperone proteins!

Question 29

Give a specific example of receptor trafficking;

Answer 29

For example: SAP97 binds simultaneously to the microtubule motor Kif1b and to the GluR1 subunit of the AMPA receptor

Question 30

Describe how PSD proteins help insert receptors into the membrane;

Answer 30

1. AMPA receptors are thought to be ‘stored’ in vesicles in the spine head
2. A PSD protein termed ‘Stargazin’ is thought to bind AMPA receptors and direct their insertion into the postsynaptic membrane
3. AMPA receptors then become ‘stabilised’ at the PSD through interactions with multiple PSD proteins that form complexes around the receptors

Question 31

Are receptors inserted directly into the membrane?

Answer 31

No most move across via lateral diffusion and form stabilising interactions with the PSD

Question 32

How do PSD proteins act as signalling molecules?

Answer 32

1. Many PSD proteins act together to form signalling complexes that operate downstream of glutamate receptors
2. Distinct PSD protein complexes are likely assembled around each subtype of receptor. Therefore each receptor class can transmit different signals into the postsynaptic cell.

Question 33

What property of the PSD allows it to be a signalling complex?

Answer 33

Protein:Protein domains can have IC signalling capacity therefore creating signalling complexes.

Question 34

How does the PSD aid receptor removal?

Answer 34

1. Glutamate receptors must be uncoupled from the PSD proteins that are stabilising it in the membrane
2. Receptors can then be removed via endocytosis

Question 35

What determines how the receptors are removed?

Answer 35

Evidence suggests that post-translational modifications of AMPA receptors regulates whether ‘stabilising’ or ‘endocytic’ PSD proteins can bind to the AMPA receptor

•Protein phosphorylation of the GluR2 subunit of the AMPA receptor dictates whether it can bind the endocytic protein GRIP.