Canonical and F⁻ transporting CLCs. (A) High-resolution structure of a canonical CLC Cl⁻/H⁺ antiporter, CLC-ec1 (PDB ID: 1OTS), reveals the conserved Glu, Ser, and Tyr Cl⁻ coordinating residues. The green sphere represents the Cl⁻ ion. (B) Phylogenetic tree of the CLC^F clade, showing N-T and M-V subclades. Homologues used in this study are indicated. (C) Sequence alignment of several CLC^F homologues in the helix D and helix F regions. Yellow boxes highlight residues differing between CLC^F subclades and strictly conserved within them. Sequences in same region of canonical CLCs of known structure are shown below, with red boxes denoting the Cl⁻-coordinating Ser residue.