Cys-Loop Activation Flashcards
(7 cards)
1
Q
The pore
A
- M2 is a channel-lining alpha helix
- many larger ions bind the channel and block function e.g. chlorpromazine (antipsychotic, activity in M2)
- 9’ leucine conserved in all cys-loop receptors
- selectivity transition mutant with 3 amino acid changes will reverse selectivity of 5-HT3R and nAChR = switch to anion selectivity
rings of negative charge in nAChR
- intermediate ring most important
- extracellular and intracellular are much less important
2
Q
Channel opening + loop C
A
- ligand binding alters structure of the binding site = loop C closure
- studies of AChBP show agonist binding causes loop C closure over the binding pocket
- loop C is not sufficient to drive gating
- coupling of loop C to M1 causes conformational change in M2 pore-lining helix
3
Q
Studying loop C
A
movement of loop C and subunit twisting
- studied by spraying ACh before plunging in ethylene
- ACh opens channels
- ethylene freezes in this state
- ferretin shows where the ACh has bound
- freezing allows visualisation of open channels
4
Q
Channel opening summary
A
- ligand binding alters binding site structure
- subunit twists
- base of ECD pushed outwards
- M2-M3 loop moves out radially
- M2 twists, removing the hydrophobic girdle from centre of pore
5
Q
GLIC
A
- GLIC opened by pH
- 3 histadines in each subunit
- mutation to alanine = pH shift to a more acidic pH
- only M3 mutant halts function completely
- weakening M2-M3 H-bond = reactive destabilisation of open state
- unconventional amino acid mutageness prevents this
- methylating histadine = no function
- histadines important in forming H-bond to allow channel function
6
Q
The intracellular domain
A
- plays critical role in localisation of receptors at synapses
- can also interact with modulatory proteins to influence function
- e.g. RIC3 = resistance to inhibitors of cholinesterase
RIC3 inhibits 5-HT3R but not GLIC
- GLIC has no ICD
- adding 5-HT3 ICD to GLIC allows RIC3 to inhibit
- suggests RIC3 action through ICD
- ICD portals can be seen in low res nAChR structure
- framed by alpha helices
- influence conductance
7
Q
5-HT3A vs AB single channel conductance
A
- 5-HT3A vs AB have different single channel conductances
- A = lots of Arg
- B = no positive residues
- positive Arg line portal in A and inhibit cation flux
- B has bigger portal as no positive charges therefore more conductance
- replacement of Arg with amino acids found in B rescues conductance
- portals in M3-M4 loop play a role in conductance
