User:Amy Kerzmann/Sandbox 3
From Proteopedia
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| 1bl8, resolution 3.20Å () | |||||||||
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| Resources: | FirstGlance, OCA, RCSB, PDBsum | ||||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||||
Contents |
Background
Initial observations of the extraordinary selectivity of some ion-conducting channels for potassium baffled many scientists. How could such proteins permit the passage of potassium ions while restricting smaller sodium ions from being transferred across the membrane?
The crystal structure of the Streptomyces lividans potassium channel illuminated the principles of ion selectivity when it was solved in 1998 (PDB:1bl8).[1] To further demonstrate the importance of this structure, the 2003 Nobel Prize in Chemistry was awarded to Roderick MacKinnon for the work performed in his HHMI laboratory at Rockefeller University.
Channel Structure
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As described by Doyle, et al in their original paper, the potassium channel forms an "inverted teepee, or cone" with the widest portion facing the extracellular space.[1] Almost the entire structure is buried within the lipid bilayer, which is evident when the structure is colored according to the of each sidechain (hydrophobic residues are shown in grey and hydrophilic in purple.) The protein spans approximately 34 angstroms of the lipid bilayer [1], based on the distance between the highlighted in black.
The potassium channel is also a homotetramer, which means that it is comprised of identical protein chains or monomers, each shown in a different color. These monomeric units assemble to form a functional protein with around the longitudinal axis, which is best viewed from either membrane surface. As a result, each of the channel-lining residues appears as a ring of four identical sidechains. This principle is represented by the conserved amino acids that function as selectivity filters within the cavity. Additional , and sidechains line the channel. We will examine each of these conserved sites in greater detail under the "Channel Function" heading. It is also important to note that analysis of a of these residues reveals some hydrophobic patches within the cavity.
Each is predominantly and lacks beta strands. When viewed in (where the N-terminus is blue and the C-terminus is red), one can see that both termini are located on the cytosolic side of the membrane. Note that the two C-terminal helices form the central core of the channel and that the region between them lines the cavity, making contacts with the migrating potassium ions.
Channel Function
Here's how it works.
Gating Mechanism
Details of the voltage-gated mechanism go here.
Selectivity Filter
Comparison of the hydrated states of potassium and sodium.
References
