K+ channel

Crystal structure of a mammalian voltage-dependent Shaker family K⁺ channel, Kv1.2.

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Introduction

Potassium channels consist of four identical subunits, each made up of six, linked helical segments. Potassium ions flow through the central pore of the channel, which is formed by the assembly of two helical segments from each subunit. Other helical segments form voltage sensors that detect voltage changes across the cell membrane. These voltage sensors can move to open and close the pore of the potassium channel.2 This chime model shows the important molecular and structural components of one of the four subunits that makes up the potassium channel.

For more information see Biochemistry Online: Chapter 9B - Signal Transduction: Neurochemistry

Wire Frame
Spacefill With K⁺
Backbone with K⁺
Backbone and sidechains
View S1 greenblue
View S2 orange
View S3 grey
View S4 cyan
View S4-S5 red
View S5 purple
View S6 yellow

The alpha helices from the various subunits interlace around one another. The voltage sensor domains (S1 through S4) of the potassium channel are independent of the pore except through their attachments with the S4-S5 linker, which enable them to perform mechanical functions on the pore.1

View Arg 294
View Arg 297
View Arg 300
View Arg 303

These four arginine residues account for most of the gating charge on the voltage sensor.1 These positively charged arginine residues move through the membrane, from the extracellular to intracellular position, due to changes in the electrochemical gradient of the transmembrane. The pore opens when the inside of the membrane is positive and the positive charges (arginines) get pushed outside. The pore closes when the membrane is negative on the inside and the positive charges (arginines) are drawn back inside. The movement of these arginines is initiated by the S4 helix, a voltage sensor, which with the help of the other helices opens and closes the pore by working on the positively charged arginines.1

View Phe 302
View Phe 305

These residues are important in establishing the correct position of the S4 helix.1

View S6 Pro-Val-Pro stick mode

This sequence of the S6 helix makes a platform for the S4-S5 linker helix (shown in red wireframe). It allows inner helices to curve so they can interact correctly with the S4-S5 linker helix. This interaction is necessary for the coupling of the voltage-sensor movements to the opening and closing of the pore.1

Crystal structure of a mammalian voltage-dependent Shaker family K+ channel, Kv1.2.

Crystal structure of a mammalian voltage-dependent Shaker family K⁺ channel, Kv1.2.