Structure and function of an Arabidopsis thaliana sulfate transporter.

Plant sulfate transporters (SULTR) mediate absorption and distribution of sulfate (SO) and are essential for plant growth; however, our understanding of their structures and functions remains inadequate. Here we present the structure of a SULTR from Arabidopsis thaliana, AtSULTR4;1, in complex with SO at an overall resolution of 2.8 Å. AtSULTR4;1 forms a homodimer and has a structural fold typical of the SLC26 family of anion transporters. The bound SO is coordinated by side-chain hydroxyls and backbone amides, and further stabilized electrostatically by the conserved Arg393 and two helix dipoles. Proton and SO are co-transported by AtSULTR4;1 and a proton gradient significantly enhances SO transport. Glu347, which is ~7 Å from the bound SO, is required for H-driven transport. The cytosolic STAS domain interacts with transmembrane domains, and deletion of the STAS domain or mutations to the interface compromises dimer formation and reduces SO transport, suggesting a regulatory function of the STAS domain.