Crystal Structure of a Mammalian Voltage-Dependent Shaker Family K+ Channel

Stephen B. Long, Ernest B. Campbell, Roderick MacKinnon

Presented by: Nathan LinMarch 3, 2011

What is a Shaker Kv 1.2?

• Voltage dependent potassium ion channel• 1.2 is the classification of a specific alpha

subunit• Shaker (Sh) is a gene in Drosophila

melanogaster that has a role in potassium ion channels

• When this gene is mutated, the fly will “shake” it’s legs

What is the role of ion channels?

• Integral membrane proteins• Involved in many biological processes– Component of the nervous system– Action potential creation– Initiating intracellular signalingBut more specifically….During an action potential, return the depolarized

cell back to it’s resting state

Structure of Shaker Kv 1.2

• 3 main units– Voltage Sensing– T1: stabilizes channel structure– Beta subunit: Forms a complex with T1 that is a

tetramer of proteins that are related to oxido-reductases• Role not clearly understood

What is a Voltage Sensing Domain?

• VSDs are coupled to pore domains– Coupled via S4-S5 linker

• Sense stimuli that results in a conformational change and tells the pore domain to open or to close

• Corresponds to S1-S4

Structure continued

• Pro-X-Pro– Conserved sequence on helix S6

• X = Valine (in Kv 1.2) – Glycine (in KvAP)

• Role: curvature

Kv 1.2 = redKcsA = greyKvAP = blue

Structure continued

• Two main ideas:• K+ selectivity filter is conserved• Inner pore varies in conformation– Diameter of 12 Angstroms suggests..– Kv 1.2 is in “open” conformation– When closed, prevents Ag+ ions from crossing

(atomic radius = 1.15 Angstroms)

Structure continued

• Side Portals sit above the T1 domain• Connects pore to the cytoplasm• Diameter of 15-20 angstroms• Attract cations since rim is mainly negative• Leads to the next topic about structure….

N-type or “ball and chain” inactivation

• Classification of gating property– Dependent on Alpha subunit

• Kv 1.2 = delayed rectifier• Kv 1.4 = A-current • Work with Kv 1.4 gave rise to how we

understand Kv 1.2• N-terminus can enter inner pore and

inactivate Kv channel

• Membrane depolarizes, pore opens and conducts K+ ions, channel inactivates.

• This is when the N-terminus sequence “snakes” in

Glutamate / Aspartate = red = -Arginine / Lysine = blue = +

Conclusion

• Potassium channels have many important roles

• Beta subunit not well understood• All we know now is that it controls inactivation• Active site has NADP+ as a cofactor so may

have catalytic function• Future testing required

References• Long, B., Stephen, Campbell, B., Ernest, Mackinnon, Roderick. 2005. Crystal

Structure of a mammalian Voltage-Dependent Shaker Family K+ Channel. Science. 309: 897-902

• Strang, C., Cushman, S.J., DeRubeis, D., Peterson, D., Pfaffinger, P.J. 2001. A central role for the T1 domain in voltage-gated potassium channel formation and function. J Biol Chem. 276: 28493-28502