Mol and Cel Neuro 1

Page 1

Potassium channel family tree

Structure

The K+ channel needs 4 subunits to come together

The subunits have an intracellular and extracellular ends.

The hole in the middle of the subunits becomes the permeable pore.

They have voltage-dependant activation S4 and voltage-dependent inactivation (two forms N & C-type)

4 subunits must combine to form a functional channel with the exception to 2 pore subinits.

Key Features:

-Trans-membrane protein composed of 4 subunits contain an intergral ion-permeable pore

-Pore is selective for K+ions and has a conserved sequence GYG motif

-Conductance drives the membrane potential toward EQ

-Unitary conductance from 5-200

- There are many conserved subunits.

Page 2

The Pore: KesA K+ Channel Structure

Doyle et al

They used a bacterial potassium channel and the represetation they came to gave structural feedback

Mechanisms of ion selectivity:

4 key features:

- charge . Helix dipoles allow for attraction

-size, Multiple ion occupancy

- Customized oxygen cages for crystalisation. it has to lose these to pass through the wall. It has automatically configured the charges so that the ion cannot tell between crystalisation into the vestule of the pole. It finds its preffered site via the dipole

- Plenty of water , ions dont like being in lipid

All of these have been perfected to maximize ion selectivity.

Potassium channels act as an enzyme to assist potassium channel pass through membranes.

It is important to use the multifuctional properties of potassium channels so other ions e.g sodium cant pass through. E.g sodium is smaller but it is not a snug fit so it cannnot pass through

Page 3

N-terminal inactivation

Inactivated state is not the same as closed. There are two forms of inactivation

N type is an N-terminal ball peptide Inactivated it has a binding site inside the pore , this can be done by an accesory protein.

C type is the narrowing of the channel

Page 4

All potassium channels have other subunits

Key concepts

We need 4 subunits for a channel. Charge travels and allows for the pore to be open and allow for potassium to bind and travel through the channel.

Theres 2 ways for the channel to close. it can deactivate which can be reactivated or inactivated where it can no longer be live again.

4 major families of voltage-gated K+ channels

they can be split into low voltage activated and high voltage activated.

KV1 can control the threshold for a neuron because they have a LVA .

HVA result in action potentials so HVA K+ channels regulate duration of action potentials.

Tetrathylammonium TEA is an antagonist for potassium channel. The Nitrogen interacts with the pores to block them.

Mamba snakes have a potassoum blocker called Dendrotoxin hich binds to some KV subunits which are in the brain.