According to a press release, a team of scientists led by Howard Hughes Medical Institute (HHMI) investigator Roderick MacKinnon at The Rockefeller University has determined the three-dimensional structure of the chloride ion channel. Their work was reported in the 17 January 2002, issue of Nature. Additional information is available in a second press release from Rockefeller University, where the MacKinnon lab is located. The same team worked out the details of the function of another type of ion channel, or molecular sorter, for potassium in November 2001.
The researchers discovered the chloride ion channel has a completely different structure from the potassium ion channel. While the potassium ion channel has one large single pore with a water-filled, pyramid-shaped cavity, the chloride ion channel has two pores, each shaped like an hourglass with a narrow constriction at the center. The scientists also discovered the arrangement of the protein subunits that make up the channel are arranged entirely differently in the two types of channels. In the potassium ion channel, four protein subunits contribute to a single pore. In the chloride ion channel, each protein subunit has its own pore and the two halves of the subunit have opposite orientations in whatís called two-fold rotational symmetry. Future experiments in MacKinnonís laboratory will focus on determining how the chloride ion channel opens and closes to maintain the appropriate concentration of ions inside the cell.
Similar work on a membrane channel specific for water molecules was reported here on Nanodot in December 2001.