MacKinnon, Roderick (1956-…), an American biophysicist, won a share of the Nobel Prize in chemistry for determining the structure of microscopic channels that allow charged atoms called ions to pass into and out of living cells. MacKinnon shared the prize with the American biochemist Peter Agre.
MacKinnon studied proteins in the cell membrane that form a tunnel through which ions pass. These ion channels contain selectivity filters, tiny structures that admit only a certain kind of ion. MacKinnon was particularly interested in the potassium channel, which admits only potassium ions.
MacKinnon studied the proteins that make up the potassium channel using a technique called X-ray crystallography. He formed the proteins into crystals, then bombarded them with X rays. By studying the patterns of X rays scattered by the crystals, MacKinnon determined the structure of the proteins.
MacKinnon described the potassium channel in 1998. His studies revealed how the channel admits potassium ions but not sodium ions, which are smaller than potassium ions. In a water solution, ions form stable groups with nearby water molecules. MacKinnon found that the oxygen atoms that line the channel’s selectivity filter mimic the oxygen atoms in these water molecules. The atoms in the filter are spaced at the same distance as the water molecules are spaced around a dissolved potassium ion. This allows potassium ions to remain stable while passing through the filter. Sodium ions, on the other hand, are stable when the oxygen atoms in the water molecules are held more closely. The sodium ions remain in the water solution instead of entering the filter, where the wider gaps between oxygen atoms would make sodium ions less stable. MacKinnon also discovered a gatelike structure at one end of the tunnel that enables the channel to open and close.
MacKinnon also described other kinds of ion channels. Cells use these channels to generate an electric pulse by passing ions through the cell membrane. Some cells, such as nerve cells, use these pulses to transmit signals. MacKinnon’s research helped scientists understand diseases of the heart and nervous system that may be caused by defects in ion channels.
MacKinnon was born on Feb. 19, 1956, in Burlington, Massachusetts. He earned a B.A. degree in biochemistry from Brandeis University in Waltham, Massachusetts, in 1978 and an M.D. degree from Tufts University Medical School in Boston in 1982. From 1989 to 1996, he taught at Boston’s Harvard Medical School. MacKinnon became a professor at Rockefeller University in New York City in 1996.
