High-level expression, functional reconstitution, and quaternary structureof a prokaryotic ClC-type chloride channel

ClC-type anion-selective channels are widespread throughout eukaryotic orga nisms. BLAST homology searches reveal that many microbial genomes also cont ain members of the ClC family. An Escherichia coli-derived ClC Cl- channel homologue, "EriC," the product of the yadQ gene, was overexpressed in E. co li and purified in milligram quantities in a single-step procedure. Reconst itution of purified EriC into liposomes confers on these membranes permeabi lity to anions with selectivity similar to that observed electrophysiologic ally in mammalian ClC channels. Cross-linking studies argue that EriC is a homodimer in both detergent micelles and reconstituted liposomes, a conclus ion corroborated by gel filtration and analytical sedimentation experiments .