Chloride's hourglass

Chloride channels (ClC Cl^-) are widespread in both prokaryotic and eukaryotic cells but the mechanisms behind their ion selectivity remain unclear. In January 17 Nature, Raimund Dutzler and colleagues from Rockefeller University, New York, show the crystal structure of a chloride channel that gives an insight into how these proteins work.

Dutzler et al. studied the 3 Å resolution structures of two prokaryotic ClC Cl^- channels from Salmonella enterica serovar typhimurium and Escherichia coli. They found that CIC Cl^- channels are shaped like an hourglass with a narrow constriction at the center and two pores at each side. In addition, the pore subunits have an antiparallel architecture and filter the Cl^- ion by a combination of electrostatic interactions and chemical coordination with nitrogen atoms and hydroxyl groups (Nature 2002, 415: 287-294).

"This is a spectacular breakthrough" [...] but "the details of the ion-permeation process, including whether or not several ions ...