The potassium channel is a 4-subunit, trans-membrane protein that allows the rapid passage of potassium ions — but not sodium ions — across the membrane. This protein is made up of 4 identical subunits with a channel running through the center. Carbonyl oxygen atoms in the channel replace the water molecules that normally surround the hydrated potassium ion, allowing the ions to rapidly pass through the channel. The potassium ion interacts simultaneously with 4 carbonyl oxygen atoms (1 from each subunit), thereby stripping the potassium of water molecules as it passes through the channel. Although sodium ions are smaller than potassium ions, they are excluded from the channel because they can’t interact simultaneously with all 4 carbonyl oxygens. Potassium channels are important in the nervous system as well as in drug interaction and targeting studies.

Each of the 4 identical subunits in this 3-D protein structure is a different color (white, green, yellow, and blue). Carbonyl oxygen atoms of Thr75, Val76, Gly77, Tyr78, and Gly79 that facilitate potassium movement are shown in red. The 4 potassium ions are shown in purple.

The 2003 Nobel Prize in Chemistry was awarded "for discoveries concerning channels in cell membranes" jointly with one half to Peter Agre "for the discovery of water channels" and with one half to Roderick MacKinnon "for structural and mechanistic studies of ion channels". Dr. MacKinnon was working on ion movement through channels when he determined the structure of the potassium channel from Streptomyces lividans in 1998. 

This 3.75'' model is made of plaster by rapid prototyping and should be handled with care. Mini models will break if dropped, held tightly or handled roughly. Its PDB file is 1BL8.pdb.