Sulfate permease

The sulfate permease (SulP) family (TC# 2.A.53) is a member of the large APC superfamily of secondary carriers. The SulP family is a large and ubiquitous family of proteins derived from archaea, bacteria, fungi, plants and animals. Many organisms including Bacillus subtilis, Synechocystis sp, Saccharomyces cerevisiae, Arabidopsis thaliana and Caenorhabditis elegans possess multiple SulP family paralogues. Many of these proteins are functionally characterized, and most are inorganic anion uptake transporters or anion:anion exchange transporters. Some transport their substrate(s) with high affinities, while others transport it or them with relatively low affinities. Others may catalyze SO2−4:HCO−3 exchange, or more generally, anion:anion antiport. For example, the mouse homologue, SLC26A6 (TC# 2.A.53.2.7), can transport sulfate, formate, oxalate, chloride and bicarbonate, exchanging any one of these anions for another. A cyanobacterial homologue can transport nitrate. Some members can function as channels. SLC26A3 (2.A.53.2.3) and SLC26A6 (2.A.53.2.7 and 2.A.53.2.8) can function as carriers or channels, depending on the transported anion. In these porters, mutating a glutamate, also involved in transport in the CIC family (TC# 2.A.49), (E357A in SLC26A6) created a channel out of the carrier. It also changed the stoichiometry from 2Cl−/HCO−3 to 1Cl−/HCO−3. The sulfate permease (SulP) family (TC# 2.A.53) is a member of the large APC superfamily of secondary carriers. The SulP family is a large and ubiquitous family of proteins derived from archaea, bacteria, fungi, plants and animals. Many organisms including Bacillus subtilis, Synechocystis sp, Saccharomyces cerevisiae, Arabidopsis thaliana and Caenorhabditis elegans possess multiple SulP family paralogues. Many of these proteins are functionally characterized, and most are inorganic anion uptake transporters or anion:anion exchange transporters. Some transport their substrate(s) with high affinities, while others transport it or them with relatively low affinities. Others may catalyze SO2−4:HCO−3 exchange, or more generally, anion:anion antiport. For example, the mouse homologue, SLC26A6 (TC# 2.A.53.2.7), can transport sulfate, formate, oxalate, chloride and bicarbonate, exchanging any one of these anions for another. A cyanobacterial homologue can transport nitrate. Some members can function as channels. SLC26A3 (2.A.53.2.3) and SLC26A6 (2.A.53.2.7 and 2.A.53.2.8) can function as carriers or channels, depending on the transported anion. In these porters, mutating a glutamate, also involved in transport in the CIC family (TC# 2.A.49), (E357A in SLC26A6) created a channel out of the carrier. It also changed the stoichiometry from 2Cl−/HCO−3 to 1Cl−/HCO−3. All SulPs are homodimers. where two subunits do not function independently. The dimeric structure probably represents the native state of SulP transporters. A low-resolution structure of a bacterial SulP transporter revealed a dimeric stoichiometry, stabilized via its transmembrane core and mobile intracellular domains. The cytoplasmic STAS domain projects away from the transmembrane domain and is not involved in dimerization. The structure suggests that large movements of the STAS domain underlie the conformational changes that occur during transport. The bacterial proteins vary in size from 434 residues to 573 residues with only a few exceptions. The eukaryotic proteins vary in size from 611 residues to 893 residues with a few exceptions. Thus, the eukaryotic proteins are usually larger than the prokaryotic homologues. These proteins exhibit 10-13 putative transmembrane α-helical spanners (TMSs) depending on the protein.