2.A.53.3.13
Fumarate (Na⁺-independent anion) transporter, SLC26dg of 499 aas and 14 TMSs.  It has an N-terminal Sulfate-tra-GLY domain with a glycine motif of unknown function and a C-terminal STAS (sulfate transporter and antisigma factor antagonist) domain.  The membrane-inserted domain consists of two intertwined inverted repeats of seven transmembrane segments, each resembling the fold of the (unrelated?) transporter, UraA. The structure shows an inward-facing, ligand-free conformation with a potential substrate-binding site at the interface between two helix termini in the center of the membrane (Geertsma et al. 2015). This structure defines the common framework for the diverse functional behavior of the SLC26 family.