Lecture 5 - Ion Channel Structure and Function Flashcards
What are frog cells called?
Ouzytes
What can we do with ouzytes?
They are very large cells, around 1mm, so makes them easy to work with
We can clone and express ion channels in them, and then carry out the patch clamp technique, ouzytes don’t contain many ion channels so we can be confident the ion channel we are observing is the ion channel of interest that we have expressed
What are proteins formed from?
Amino acids which can combine to produce protein structures e.g. alpha helices and beta pleated sheets
How can we see which areas are hydrophobic and hydrophilic in a protein?
Based on the charges of amino acids
Hydrophobic in lipid component of the membrane, Hydrophilic faces extracellular fluid
What is the structure of a K+ channel?
6 membrane spanning alpha helices each described as a number, S1 at the left S6 on the right
On the left of the structure we have NH2, on the right of the structure we got the carboxyl COOH
6 alpha helices form an alpha subunit, then 4 alpha subunits come together to form the K+ ion channel
What is the structure of the KCNQ1 Potassium Channel?
Made of 4 alpha subunits and 2 beta subunits
There are additional structures that give the ion channel different properties e.g. faster speed of conduction, which drugs the channel can bind
The pore is in the middle of the alpha subunit
Where are the NH2 and COOH of Potassium channels found?
Intracellular membrane
What is special about S4?
It has a common sequence across many different species with the K+ channel
Mutations in this region affect the voltage dependence of the ion channel
How does the pore of a potassium channel open?
As the electrical aspects change on either side of the membrane, the +ve arginine amino acids in the sequence move towards the extracellular surface
As S4 moves towards the surface, it will pull on S5 which then pulls on S6
So its the physical movement of these structures that lead to the pore opening
S6 also have a hinge on it which is high in glycine allowing the components to hinge
What is the pore region?
A loop which doesn’t of all the way through the membrane between S5 and S6
What is selectivity of an ion channel?
Each channel only lets through specific ions
How do ions pass through the ion channel?
When ions are in fluid, water is strongly attracted to the ion in solution
+ve ions are going to be attracted to the negative charge carbonyl structure, so ions are going to be drawn into the mouth of the ion channel
The ions are still surround by their salvation shell as they are drawn into the mouth of ion channel
The potassium channel signature sequence provides the equivalent to the salvation shell, which allows the ions to comfortably fit in the pore, with the pore providing the oxygen molecules which were previously provided by the solvation shell
As the ion leaves the other side, it picks back up its solvation shell
What is the Potassium channel signature sequence?
Conserved sequence of amino acids that seems to be unique to the potassium ion channels -threonine, valine, glycine, tyrosine, glycine
How are potassium ion channels inactivated?
There is a peptide ball on the end of a chain in the amino terminal, movement of this structure blocks off the channel, so when inactivated, the peptide ball has swung into the pore, and blocked it, so ions can’t pass through
What speed are ECGs recorded at and why?
25mm/s, allows us to make measurements of the amount of time it takes for certain activities to occur
