1. Lecture 19
Synaptic transmission, vesicle fusion and cycling
Why selectivity may not be important?
Thermodynamics of channel gating by ligand
Structure of Acetylcholine-binding protein (AChBP)
Latest about nicotinic Ach receptor

2. Depolarization
EPSP
Erest
Hyperpolarization
IPSP

3. mutation in Dynamin

5. The Docking Complex vesicle plasma membrane
SNARE proteins form coiled-coils
plasma membrane
from A. Brunger

7. Postsynaptic ionotropic receptors:
Nicotinic ACh receptor (nAChR)
Glutamate receptor (GluR)
AMPA, NMDA subtypes
GABAA receptor
Glycine receptor
excitatory (cation channels)
inhibitory
(Cl- channels)

8. K+ Cl- K+ Cl- What is driving force? E – actual membrane potential I V
EK = 0
E (mV) K+
Cl- I V
EK < 0
driving force
E – actual membrane potential

9. Hmmm, …but nAChR passes both of ions! Why does it lead to excitation?
- it is known that Na+ influx causes depolarization, and K+ efflux causes hyperpolarization. Yes.
Hmmm, …but nAChR passes both of ions! Why does it lead to excitation?
ENa = +60 mV
EK = -90 mV
Erest = -70 mV
Ethreshold

10. nACh R (Na+, K+ channel) R AR A2R A2R* A2D open gate closed
desensitized
from Unwin

13. L0, LA – equilibrium constants
KA, JA – binding constants

14. C O LO ΔGC→O = -RT ln([O]/[C])=-RT lnL0
In the absence of ligand the O state is unfavorable, openings are rare
ΔGC→O = -RT ln([O]/[C])=-RT lnL0

15. C O LO ΔGC→O = -RT ln([O]/[C])=-RT lnL0
In the absence of ligand the O state is unfavorable, openings are rare
ΔGC→O = -RT ln([O]/[C])=-RT lnL0

16. ΔGC→AC = RT ln([AC]/[A][C])=RT lnKA
Initially binding of the ligand occurs with low affinity
ΔGC→AC = RT ln([AC]/[A][C])=RT lnKA

17. ΔGAC→AO = -RT ln([AO]/[AC])=-RT lnLo
Binding makes the AO state more favorable than AC, openings are frequent
ΔGAC→AO = -RT ln([AO]/[AC])=-RT lnLo

18. ΔGAC→OC = -RT ln([AO]/[AC])=-RT lnLA
Binding makes the AO state more favorable than AC, openings are frequent
ΔGAC→OC = -RT ln([AO]/[AC])=-RT lnLA

19. The change in equilibrium constant between the states equals to the change in affinity to the ligand that occurs with opening. Consider what should be strong agonist, weak agonist or competitive blocker

20. In Molluscs:
AChBP is released upon ACh release and then sequesters ACh
from Sixma et al.

21. AChBP: 210 aa per subunit, pentamer
from Sixma et al.

24. nicotine
carbamylcholine