Family 2.A.47 - The Divalent Anion:Na+ Symporter Family       

Family ID: 52636

Functionally characterized proteins of the DASS family transport (1) organic di- and tricarboxylates of the Krebs Cycle as well as dicarboxylate amino acid, (2) inorganic sulfate and (3) phosphate. These proteins are found in Gram-negative bacteria, cyanobacteria, archaea, plant chloroplasts, yeast and animals. They vary in size from 432 amino acyl residues (M. jannaschii) to 923 residues (Saccharomyces cerevisiae). The three S. cerevisiae proteins are large (881-923 residues); the animal proteins are substantially smaller (539-616 residues), and the bacterial proteins are still smaller (461-612 residues). They exhibit 11-14 putative transmembrane a-helical spanners (TMSs). An 11 TMS model for the animal NaDC-1 has been proposed (Pajor, 1999). This and the other NaDC isoforms cotransport 3 Na+ with each dicarboxylate. Protonated tricarboxylates are also cotransported with 3 Na+. Several organisms possess multiple paralogues of the DASS family (e.g., 4 for E. coli; 2 for H. influenzae, 3 for S. cerevisiae, and at least 4 for C. elegans).

The phylogenetic tree for the DASS family reveals six clusters as follows: (1) all animal homologues; (2) all yeast proteins; (3) a functionally uncharacterized protein from Ralstonia eutrophus; (4) three E. coli proteins plus one from H. influenzae and one from spinach chloroplasts (the SodiT1 oxoglutarate:malate translocator); (5) an E. coli Orf that clusters loosely with a sulfur deprivation regulated protein of Synechocystis, and (6) an M. jannaschii protein that clusters loosely with an H. influenzae Orf.

Distant homologues of DASS family proteins may include members of the Ars (arsenite exporter) (TC #3.A.4) family as well as the NhaB (TC #2.A.34) and NhaC (TC #2.A.35) Na+/H+ antiporter families. The DASS family is therefore a member of the ion transporter (IT) superfamily (Rabus et al., 1999).