Lecture Notes

Membrane transport II
Learning objectives:

1. Describe the different mechanisms of regulatory control of ion channels
2. Explain the structural basis of voltage gating, using eukaryotic K V channels as an example
3. Describe the differences between the three conformational states of a
4. eukaryotic voltage-gated K+ channel
5. Compare and contrast the basic mechanisms of K + channels and the glucose transporters
6. Explain the mechanism of Na+/K+ ATPase
7. Define the term ‘secondary transport’ and explain how the driving force for this type of transport is generated

Voltage-Gated K+ Channels from Eukaryotes

• Are called KV channels
• Four identical or homologous subunits, each subunit containing six transmembrane a-helices
• Two functionally distinct domains:
- Pore domain (helices S5, S6 and P segment homologous to helices M1, M2 and P segment in KcsA)
- Voltage sensing domain consisting of helices S1 to S4

, Three-Dimensional Structure of the KV1.2 Channel Purified from Rat Brain (activation gate open)




Gating mechanism of K+ Channels from Eukaryotes

 Amino acid sequence of S4 helix shows a number of positively charged amino acid residues