L12 - PSD

Question 1

What does post-synaptic specialization refer to?

Answer 1

Membranes and cytoplasmic proteins clustered immediately opposite release sites or active zones at synapses.

This includes:

• Ligand gated ion channels
• Anchoring proteins
• Cytoskeleton (for structure)
• Regulatory proteins (alter activity of ligand gated ion channel)

Question 2

What’s the difference in PSD thickness between glutamate and GABA?

Answer 2

Glutamate - thick

GABA - thin

Question 3

Is there more or less different proteins at the excitatory synapses?

Answer 3

More, excitatory - 1000, inhibitory - 250

Question 4

What roles do many PDS proteins play?

Answer 4

They are cell adhesion molecules - hold pre and post synaptic structures together. They have intracellular tails that are involved with synapse functionality.

Question 5

There are many rare mutations in synaptic function genes. Name two molecules mutated in autism

Answer 5

• Shank - responsible for 1% of all autistic patients

- Neuroligin 3

Question 6

Neuroligins - what do they do? What do they bind to - across the synaptic cleft and intracellularly?

Answer 6

• They organise PSD
• 5 different isoforms on X chromosome
• They form dimers (homo or hetero), binding across synaptic cleft to Neurexin (a or b form, b more favourable) which is on the presynaptic terminal.
• Intracellularly, they’re bound to PSD95 aka SAP-90 (synapse-associated protein) aka DLG4 (Disks large homolog 4)

Question 7

Neuroligins 1, 2, 3 and 4 - where is each one found? (excitatory or inhibitory)

Answer 7

1 - glutamatergic synapses and some cholinergic (nicotinic) synapses in PNS
2 - SOME inhibitory synapses - GABA (preferentially)
3 - BOTH excitatory and inhibitory, forms heterodimers with neuroligin 1
4 - Glycinergic synapses in retina - amacrine and horizontal cells (preferentially)

Question 8

PSD95 - how many PDZ binding domains? What does PDZ stand for? How long is the PDZ motif?

Answer 8

• 3 PDZ binding domains
• PDZ stands for Postsynaptic density protein 95, Drosophila disc large tumour suppressor (Dig 1) and Zona occludens protein (zo-1) - cell to cell adhesion molecule that form tight junctions
• 80-90 amino acids, longer than insulin

Question 9

Which PDZ domain do the neuroligins bind to? What about AMPA glutamate receptors? NMDA?

Answer 9

Neuroligins - 3rd one
AMPA - 1st one -Neuroligin/neurexin interaction holds AMPA receptors in place
NMDA - 2nd one - it is mobile

Question 10

nNOS

Answer 10

Neuronal nitric oxide synthase, NO (NT in periphery and neuromodulator in the brain), hence is involved in synaptic density. Also implicated in synaptic plasticity and neuroprotection. It also binds to one of the PDZ binding domains in PSD95.

Question 11

PSD95 staining is punctate

Answer 11

PSD95 staining is punctate

Question 12

List the things PSD95 can bind to (5)

Answer 12

• Neurogilins
• NMDA receptors
• nNOS
• Calcium-calmodulin protein kinase II (CaMKII) (Regulates NMDA and AMPA cycling and implicated in memory formation)
• Shank proteins, indirectly via GKAP -Shanks can also bind directly to neuroligins

Question 13

Shanks -what are they? They bind via homer to what two structures?

Answer 13

• Cytoskeletal proteins coupling via cortactin to the actin cytoskeleton
• Bind via Homer to metabotropic glutamate receptors
• Also via Homer to IP3 receptors on the smooth ER (Regulate Ca release)
• Mutations in Shank proteins can cause presynaptic changes signalling via neuroligin to presynaptic neurexins

Question 14

What is the key organising molecules specific for GABA and glycine synapses?

Answer 14

Gephyrin

Question 15

Both GABA and glycine receptors are from the same superfamily as the nicotinic acetylcholine receptor - what kind of TM proteins? How many subunits?

Answer 15

• Pentameric transmembrane proteins

- Contain at least 2 α-subunits

Question 16

Do nicotinic synapses have postsynaptic densities like those of inhibitory synapses or those of excitatory glutamatergic synapse- PSD93 OR 95?

Answer 16

PSD93 seems to be involved in nicotinic synapses

Question 17

• Postsynaptic densities differ according the type of synapse
• Neuroligins and other CAMs form key parts of the density and signal via different pathways

Answer 17

• Postsynaptic densities differ according the type of synapse
• Neuroligins and other CAMs form key parts of the density and signal via different pathways