Glutamate Receptors Flashcards by Peter Dudley

NMDA stands for?

N-methyl-D-aspartate

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Name the 3 ionotropic glutamate receptors and what ions they are selective for

nmda (Na, K, Ca)
Ampa (Na, K, only those without GluR2 subunit allow Ca)
Kainate (Na, K)

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AMPA agonists include

AMPA

GLUTAMATE

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AMPA antagonist include

NBQX (competitive)

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NMDAR agonists include

NMDA
Glutamate
Glycine (cofactor)

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NMDA antagonists include

AP5 (competitive)

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How many subunits exist for AMPARs?

4 (GluR1-4)
Sometimes go by GluA
Splice variants exist which can mean they are either in a flip or flop variant

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How many NMDAR subunits are there?

GluN1

GluN2 (A-D)

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What NMDAR subunit dictates its properties?

Mainly GluN2

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How many subunits come together to form an NMDAR?

4 - tetremer
2xGluN1 (bind glycine)
2xGluN2 (bind glutamate)

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Draw a AMPA/NMDAR subunit structure

Extracellular N terminus
S1
TM1
TM2 (pore loop)
TM3
S2
TM4 
Intracellular C terminus

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What are the 3 domains of a ionotropic glutamate receptor subunit?

Amino N terminal domain
Ligand binding domain
Intracellular C terminal domain

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What is the function of the N amino terminal domain?

Contributes to receptor assembly (not NMDAR)

NMDAR it is important for receptor modulation and desentisation

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What is the function of the ligand binding domain?

Formed by end of the N terminal domain and extracellular loop between TM3 and 4

Acts as a clamp shell to enclose ligand when bound
Full agonist cause clamp shell to close by 20 degrees

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At -40mV what mediates glutamatergic currents? At what rate does it occur?

Fast outward inward current due to AMPARs.

At -40mV extracellular Mg2+ blocks the NMDAR

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At +40mV what channels mediate glutamatergic currents? Which direction is current?

Fast initial AMPAR
Slow NMDAR component (extracellular Mg2+ block is removed when depolarised)
Current is outwards as equilibrium potential is 0mV for both channels

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What are some unique features of NMDARs as compared to AMPARS.

Calcium permeability
Need coagonist to open
Voltage dependant
Blocked by phencyclidine- gives hallucinations

Who proposed that AMPARS are tetramers?

Rosenmund et al 1998

How did rosenmund et al discover AMPARs were tetramers?

Fast perfusion exchange from NBQX to ampa agonist
Observed how conductance increased in a stepwise manner

Closed - closed - small open - medium - large
Each step represented the dissociatation of antagonist and binding of agonist

Why were there only 3 steps in Rosenmund et al (1998) study yet they concluded AMPA was a tetramer?

Transition time from closed to small opening different than from small to medium and medium to large

C -> S = two component wait time on graph
S->M and M->L = only one exponential transition time graph

Why are AMPARS described at dimers or dimers?

2 GluA subunits must first interact at the level of the N terminal domain to then be able to interact with another dimer at the level of the S2 tranmemembrane domain to form tetramers

What is the evidence of the existence of the ligand binding domain?

What is left from the Cleavage of the linker molecules which bind s1/s2 to the rest of the protein is still able to bind glutamate with high affinity

How many glutamate are needed for full AMPA opening?

4 - each bind to 1 GluA subunit

In NMDARs which subunit bind glutamate and which binds glycine?

GluN1 binds glycine (2 glycine cofactors needed)

GluN2 binds glutamate

What can't glutamate bind to GluN1?

It is prevented by hydrophobic environment by valine and tryptophan which favour glycine

What is the difference between deactivation and desensitisation?

Both cause channel closure Deactivation requires the ligand to be removed I.e. Clearance of neurotransmitter via uptake or enzymes Desensitisation occurs when the ligand is still bound

How does glutamate open ionotropic glutamate channels?

Conformational change which open pore via subunits being pulled apart

How does desensitisation occur?

Desensitised state has a higher affinity for glutamate | Interdomain conformational change close channel pore as subunits are pulled together

Where does alternative splicing occur in the GluA subunit?

Within the S2 region

What states does alternative splicing cause?

A flip or flop state | Which changes sensitisation rate

Which splice variant causes quick desensitisation?

FLOP

Which splice variant causes a slow desensitisation?

FLIP

NMDAR receptor kinetics is a result of....

Activation Deactivation Modulated by GluN2 subunit

Work by what scientist discovered why some AMPARs are permeable to calcium?

Burnashev et al 1992

what amino acid is encoded for in the gene of GluA2?

Glutamine (Q)

mRNA modification changes this glutamine to what amino acid? Why is this important?

Arginine, which is positively charged | Therefore, since this change occurs in the pore loop region GluA2 subunits do not allow calcium influx

Why are most AMPARs impermeable to calcium?

Most contain a GluA2 subunit | Not in the hippocampus and auditory neurons

With NMDARs which aminoacid (at the same respective region to the Glua2 subunit) allows calcium permeability?

Asparagine which allows 3-4 times more calcium influx than calcium permeable AMPARS

Where does CaMKII phosphorylate glutamate receptors? What does this achieve?

GluA1 subunit Intracellular domain S831 Increases AMPAR current

Where does PKA phosphorylate glutamate receptors? What does this achieve?

GluA1 subunit S845 Increases ampa current Dephosphorylation here causes LTD via internalisation

Where does PKC phosphorylate glutamate channels? | Why is this important?

GluA2 subunit Serine 880 Promotes PICK1 binding over GRIP binding