General Structure of VDCCs

Question 1

What is the selectivity mechanism?

Answer 1

Voltage gated calcium channels have evolved this selectivity filter to allow the to recognise calcium ions over sodium ions (which are a similar size) - despite sodium channels being more abundant in extracellular solution.

Question 2

How do calcium channels achieve high ion selectivity?

Answer 2

CaVab (a bacterial calcium channel) has provided structural insight into calcium ion selectivity and permeation.

1) the structure revealed three ion binding sites for hydrate calcium lining the axis of the selectivity filter
2) repulsion between calcium ions
3) selectivity filter can oscillate between a single ion bound state with high affinity central site occupied OR two ion bound state with the central site empty - unidirectional calcium flux