Ion channel diversity III Flashcards
(29 cards)
What do all VGK+ channels contain?
5 AA sequence–> GYGVT
Which organism were VGK+ channels first cloned from?
Drosophila
How many alpha subunits does the VGK+ channel have?
4
What does the VGK+ channel mirror?
The alpha subunit of the sodium channel
How does the does the VGK+ channel mirror the alpha VGNa+ subunit?
4 alpha subunits in K+ that make up a v similar structure to the 1 alpha subunit in Na+
How many alpha subunits make up the K+ channel?
4
How many beta subunits make up a K+ channel?
3
Overall subunit makeup of a K+ channel?
4 alpha subunits, 3 beta subunits
Sizes of Na+ and K+ ions?
Na+ is smaller than K+
Why cant Na+ pass through a K+ channel?
In solution Na+ has a larger diameter hydration shell than K+–> its too big
What is a hydration shell?
Layer of water molecules that surround an ion in solution
Why does Na+ have a larger diameter hydration shell than K+?
Na+ has more tightly bound shells of water molecules
What happens to hydrated K+ ions when they approach the selectivity filter?
They lose their hydrated state
In what state does K+ move through the VGK+ channel?
An unhydrated one
How does K+ pass through the VGK+ channel?
Through coordination of oxygens on associated AAs in the selectivity filter
What does the dehydrated K+ ion associate with in the channel?
Oxygen on the carbonyl groups of AAs in the channel
What do the oxygens on the carbonyls from the AAs (that associate with the K+) do?
Mimic the oxygen from the hydrated state
Which AAs provide the oxygen for the K+ to associate w/?
The GYGVT AA motif
Why can non-hydrated sodium not pass through the VGK+ channel?
They are too small to make the interactions with the oxygen in the selectivity filter that K+ can
Width of VGNa+ channel compared to VGK+ channel?
Sodium channel selectivity filter is wider
How does Na+ pass through the filter in the VGNa+ channel?
Partially hydrated state
What enables the partially hydrated state of sodium to pass through the selectivity filter of the VGNa+ channel?
Glutamate
How does the glutamic acid in the VGNa+ channel work?
Sits within selectivity filter and attracts Na+ ion to it so Na+ can pass through in a partially hydrated state
Why can a hydrated K+ not fit through the selectivity filter of a VGNa+ channel?
The glutamate prevents it from doing so–> doesnt have the correct geometry to pass through the filter
