Figure 1.

Membrane topology model of the ClC1 monomer. The functional channel is an antiparallel-assembled homodimer. It possesses two independent ion-conducting pores each with a fast opening mechanism of its own, two selectivity filters, and two voltage sensors. The channel is functional without any other subunits. Symbols are used for mutation-caused amino acid substitutions leading to either recessive Becker or dominant Thomsen myotonia congenita. The amino acids at which substitutions occur are indicated by one-letter abbreviations. They are numbered according to the protein sequence.