Roderick MacKinnon
Roderick MacKinnon is Professor of Molecular Neurobiology and Biophysics at The Rockefeller University in New York, USA.

Ion channels:
Tiny molecular machines

In 1998 Roderick MacKinnon for the first time determined at high resolution the structure of an ion channel. As so often in biochemistry, form and function are intimately connected. By showing what the protein looked like at the atomic level, he also realised how it functions.

Only the potassium ions pass through

How can the channel let potassium ions pass but not, for example, sodium ions? The oxygen atoms in the ion filter form an environment which precisely mimics that of the potassium ion outside the filter where it is surrounded by water molecules. So the potassium ion can slip out of its “water coat” and pass through the filter without noticeable resistance.

The sodium ion, which is smaller than the potassium ion, draws water molecules more closely to itself and is too small to fit snugly between the oxygen atoms in the ion filter. Sodium ions therefore remain in the water outside the channel.