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

By Andrea Meuleners, Ann Foede, Claire Hoolihan

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.   

Original Settings

Rotation Settings

Display Settings

View All Backbone   

View All Strands   

View All Trace   

View All Ball & Stick   

View All Cartoon    Shows secondary structure which is entirely alpha helices (in purple)

Subunits    (Works best when the cartoon display is selected above.  Potassium atoms are shown in white spacefill mode.)

View S2 orange

View S3 white

View S4 light blue

View S4-S5 linker 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

Heteroatoms

Electrostatic Surface    Be patient, it takes awhile to load. Regions of negative potential are red  and regions of positive potential are blue.  Notice the negative region at the top of S5.  The positive potassium ions are attracted to this negative region and enter the channel at this location.

Original settings

Key Amino Acid Residues

Wireframe view (allows you to see the location of select amino acids in the primary structure)

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 (in stick mode) amino acids Arg 294, Arg 297, Arg 300, Phe 302, & Phe 305.   

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

View in spacefill mode   

spacefill 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

Original Settings    (click twice)

To read this article click here:  http://www.sciencemag.org/cgi/reprint/309/5736/903.pdf

To read this article click here:  http://www.sciencemag.org/cgi/content/full/309/5736/867